The following points highlight the three main divisions of Dicotyledoneae. The divisions are: 1. Apetalae 2. Polypetalae 3. Sympetalae.
Division # 1. Apetalae:
The Apetalae is an artificial assemblage of orders and families, numbering 13 and 33 respectively. Here the flowers apparently have no perianth or have a single perianth.
The main diagnostic characters of the various orders under the Apetalae are provided in the key below. It should be noted that this key represents broad statements about diversified taxa and does not indicate exceptions to the general situation.
Order 1. Casuarinales:
The order contains a solitary family, the Casuarinaceae. The characters of this order are the same as those for the family.
Order 2. Piperales:
The order is characterised by the mostly or nearly all herbaceous plants, simple leaves, racemed or spicate inflorescence and largely bisexual flowers often with bracts and without perianth.
The Piperales show no geographic or ecologic unity beyond the fact that many of the members occur in moist tropical forests, but they do not occupy such habitat by excluding other groups.
The order, as believed by Engler, signifies one of the most primitive dicot forms and hence treated by him near the beginning of the group. Core as well as Lawrence followed Engler in the placement of the order. Both Hallier and Hutchinson considered it to be a terminal and lateral offshoot of the Ranales.
Rendle thought that it is related to the Polygonales by the trimerous flower. “It is to be noted that in both the Polygonaceae and the Piperales the ovule is characteristically solitary (not always as in Piperales) and orthotropous”. An affinity has been suggested by Lotsy between the Piperales and Araceae, the item of resemblance being the inflorescence.
Cronquist (1968) claimed that the “Piperales are Magnoliidae with reduced, crowded flowers and orthotropous ovules”. The order retains the primitive uniaperturate pollen of its magnolialean ancestor. It also resembles the Magnoliales in possessing ethereal oil cells, but differs in having predominantly herbaceous plants. Within the Magnoliales again, the Lactoridaceae probably represents the closest approach to the Piperales.
However, Lactoris cannot be regarded as ancestral to the Piperales. It has well developed vessels, while Sarcandra of the Chloranthaceae is devoid of vessels. Both the Piperaceae and Saururaceae bear merely scanty endosperm and a copious perisperm (which is, however, not known in the Magnoliales).
The Chloranthaceae stands more or less apart from the other two families and can perhaps be included in the Magnoliales were it not for the fact that this family has reduced perianth and orthotropus ovules. However, these characters also make the Chloranthaceae somewhat anomalous in the Piperales.
Murty (1959) studied the development of floral organs of some members of the Piperales. He rejected the earlier idea that the bract in Peperomia typifies a staminode. According to him, the bract is hypopeltate and the solitary bundle in its stalk is a much reduced midrib. The placentation in Saururus has been variously interpreted as axile, basal, lateral or parietal; this is shown by Murty to be marginal in character.
Furthermore, he stated that two ventral bundles pass through free margins of the carpel. Another evidence in support of marginal placentation is the occasional presence of inverted bundles in the free margins. Raju (1961), while studying the morphology and anatomy of the Saururaceae, declared that the laminar placentation of Saururus represents the basic condition from which the parietal placentation of Anemopsis and Houttuynia is derived.
Order 3. Salicales
Order 4. Balanopsidales:
Due to the conglomeration of advanced and primitive characters, the position of the order is controversial. It has been thought to be related to the Juglandales or Euphorbiaceae.
The order is represented by a solitary family, the Balanopsidaceae. The family contains two genera, Balanops and Trilocularia-, the former is found in New Caledonia and Queensland and the latter in Polynesia.
There are no reported economic uses for the Balanopsidaceae.
Order 5. Leitneriales:
The order, according to Lawrence (1951), is a much reduced relic and not a primitive group. The affinity of the order has been suggested with the Salicales or Juglandales, but it is more likely that some groups in the Rosales or Geraniales or the Hamamelidaceae in the Rosales are its allies. Willis (1966) remarked that the order is an interesting relic of very obscure affinities.
The order contains only the Leitneriaceae, represented only by Florida Corkwood (Leitneria floridana), a small tree native to muddy saline swamps of south-eastern United States. The tree yields light wood used as floats for fishing nets.
Order 6. Juglandales:
There is little agreement among taxonomists as to the number of families contained in the Juglandales. Engler considered it a monotypic order with the Juglandaceae alone. This idea was also shared by both Lawrence (1951) and Core (1955). Rendle (1925) treated the order as comprising the Myricaceae and Juglandaceae.
Benson (1957) accommodated the Rhoipteleaceae and Juglandaceae within the order. According to Hutchinson (1959), the order includes the Rhoipteleaceae, Juglandaceae and Picrodendraceae. Cronquist (1968) defined the order as consisting of three families and as attempted by Hutchinson.
Mitra (1974) proposed five families under the order- Juglandaceae, Fagaceae, Betulaceae, Julianiaceae, Myricaceae. The present author supports Mitra’s delimitation of the order, but feels that the Julianiaceae should be accommodated in a separate order.
As with most other orders of the Amentiferae, the affinity of the Juglandales is not certain. The order may be primitive as considered by Engler and Prantl, but it shows a high degree of specialisation.
Order 7. Julianiales:
The order contains a solitary family (Julianiaceae) with two genera, Amphipterygium (Mexico) and Orthopterygium (Peru). It “may be primitive as suggested by Engler and Prant, but more likely it is not”. Despite the pinnately compound leaves and superficial amentiferaean traits, the family is not related either to the Juglandaceae or other taxa of the Amentiferae.
Rendle (1925) placed the group between the Juglandales and Fagales. Hutchinson (1959) included the family in his 49th order Sapindales lying between the Meliales and Loganiales. The presence of alternate imparipinnate exstipulate leaves, dissimilar male and female flowers, broad stigmatic lobes and unitegmic ovules recall strikingly what are obtained in the Juglandaceae.
While vegetative characters show no resemblance to the Fagales, the floral characters speak for an alliance with this order than with the Juglandales. The staminate inflorescence and flowers as well as minute globose pollen grains are suggestive of the species of Quercus. The pistillate flowers are crowded in an involucre, indicating the condition of Castanea and Fagus.
A relationship can be traced to the Anacardiaceae by the items of foliage, resinducts, reduced unisexual flowers, single exalbuminous seed and embryo form as well as anatomical features. The Julianiaceae is unique by the possession of the ovule ascending from the loculus-base, fruit enclosed in the enlarged involucre and seeds without endosperm.
The bark of Amphipterygium adstringens is used-medicinally as an astringent.
Order 8. Urticales:
Hallier (1905) placed the order in the Terebinthinae and Bessey (1915) in the Malvales. The order is equivalent to the Urticiflorae of Rendle (1925) as well as Engler and Diels (1936). Under this order, Engler treated families like the Ulmaceae, Rhoipteleaceae, Moraceae and Urticaceae.
Rendle conceived the order to contain also four families; here the Rhoipteleaceae was omitted and the Cannabinaceae included. Tippo (1938) indicated that the Eucommiaceae belongs to this order and so did Benson (1957). Withner (1941) excluded the Rhoipteleaceae from this order and put the family in the Juglandales.
Lawrence (1951) considered only three families (Ulmaceae, Moraceae, Urticaceae) in the order, the Cannabinaceae coming within his second family. Hutchinson (1959) created six families in the Urticales; Ulmaceae, Cannabinaceae, Moraceae, Urticaceae, Barbeyaceae, Eucommiaceae. Cronquist (1968) inserted five families by leaving out the Eucommiaceae.
According to Bechtel (1921), the members of the Urticales are a combination of primitive and advanced features. He postulated that the order is not remote from primitive entomophilous ancestors. The order is generally accepted as a natural taxon, but its position “is at the culmination of a distinct line of descent from a protoangiospermous plexus from which also ranalian descended”.
It is also regarded as phyletically advanced and a terminal group of an evolutionary line from which the Fagales has been derived. Porter (1967) suggested that the Urticales is “of ancient origin and dubious affinities”.
The Urticales is distinguished by the presence of androecium with few to several stamens and bicarpellate unilocular superior ovary with a solitary ovule.
Order 9. Proteales:
The order contains a single family, the Proteaceae. The characters of this order are the same as those for the family.
Order 10: Santalales:
The Santalales is mostly a natural group, but botanists are divided in their opinion as to its exact phyletic position. Bessey set up the families of the order in the Celastrales, deriving them from rosaceous ancestors. Hutchinson considered the order as originating from the Celastrales. Rendle treated the order as closely related to the Proteales, from which it differs chiefly in the ovary being inferior.
Due to the presence of parasitic members, Schellenberg (1932) held the view that the Santalales is not a primitive taxon. “It is not certain how much of the vegetative reduction in the Santalales has positive survival value in correlation with the parasitic habit, and how much has merely been permitted by the relaxation of selection, resulting in the accumulation of loss mutations. It may be suggested that the ovular reduction is a mere side effect of the vegetative reduction, being controlled by some of the same genes”.
The order is distinguished by the flowers generally unisexual, perianth segments small and opposite to adnate stamens and seeds with endosperm.
Different systematists have regarded the Santalales as composed of families ranging from three to ten.
Engler and Diels – Olacaceae, Opiliaceae, Octoknemataceae, Grubbiaceae, Santalaceae, Myzodendraceae, Loranthaceae.
Rendle – Santalaceae, Loranthaceae, Balanophoraceae, Cynomoriaceae.
Lawrence – Olacaceae, Santalaceae, Balanophoraceae.
Core – Santalaceae, Olacaceae, Loranthaceae, Balanophoraceae.
Benson – Olacaceae, Loranthaceae, Santalaceae, Opiliaceae, Octoknemaceae, Grubbiaceae, Myzodendraceae.
Hutchinson – Loranthaceae, Grubbiaceae, Santalaceae, Misodendraceae, Balanophoraceae.
Cronquist – Medusandraceae, Dipentodontaceae, Olacaceae, Opiliaceae, Grubbiaceae, Santalaceae, Loranthaceae, Misodendraceae, Balanophoraceae, Cynomoriaceae.
Order 11. Aristolochiales:
A great diversity of views exists as to the proper position of the Aristolochiales. According to Engler, Warming and Rendle, the order is next to the Santalales. Hallier treated it as originating from the Berberidaceae via the Lardizabalaceae. Bessey considered it as the most advanced taxon under the Myrtales—an order sprung from the Rosales.
Wettstein placed the Aristolochiales within the Polycarpicae on the basis of its annonaceous ancestry. Hutchinson set up the Aristolochiales as a separate order, adding to it also the Nepenthaceae. He held the opinion that the order represents “probably reduced Berberidales by way of Menispermaceae”.
In this order, the perianth is uniseriate and petaloid, stamens numerous and free and ovary inferior with axile or parietal placentation.
Order 12:
Polygonales:
This is a monotypic order with the characters of its single family, the Polygonaceae.
Order 13:
Centrospermales:
The taxon is distinguished by the perianth typically biseriate, ovary superior and unilocular, placentation basal or free central (with reference to the name of the present order) and embryo coiled or curved (the order called Curvem bryeae by some authors).
The order formed the 20th series of Engler’s Archichlamydeae and 13th order of Rendle’s Monochlamydeae. Wettstein followed Engler concerning the position of the order, but also incorporated the Cactaceae into it. Bessey designated the order as the Caryophyllales and supported its ranalian ancestry.
According to Hallier, the order arose from ranalian Podophylleae. Hutchinson created two orders, the more primitive Caryophyllales (derived from the Ranales and containing the Elatinaceae, Molluginaceae, Caryophyllaceae, Ficoideae and Portulacaceae) and the advanced Chenopodiales (derived from the caryophyllaceous stock and containing the Barbeuiaceae, Phytolaccaceae, Gyrostemonaceae, Agdestidaceae, Petiveriaceae, Amaranthaceae, Cynocrambaceae, Batidaceae and Basellaceae).
The Aizoaceae is primarily succulent and the Chenopodiaceae, Phytolaccaceae, Basellaceae and Portulacaceae possess many succulent members. Since most of the chenopods are halophytes with or without succulence, halophytism and succulence have been considered by Cronquist (1968) as “two expressions of the same physiological evolutionary potentialities”.
Anomalous secondary thickening resulting in the formation of concentric vascular bundles is almost a family character in the Chenopodiaceae, Amaranthaceae and Aizoaceae. This feature is not reported in the Basellaceae and Portulacaceae. It frequently turns up in the Nyctaginaceae and is more sporadic in other families.
Common embryological features of the centrospermalian plexus include the tetrasporangiate nature of anther, monocotyledonous type of anther wall development, glandular tapetum with multinucleate cells, simultaneous cytokinesis of pollen mother cells, occurrence of an air space at the base of two integuments, formation of parietal tissue, occurrence of Polygonum type of embryosac development, ephemeral antipodals, development of nuclear endosperm and Caryophyllad or Chenopodiad type of embryo development.
A distinct group of chemical compounds, betalains—betacyanins as vascular pigments in blue- violet to red series and betaxanthins as those in the yellow to orange-red series—have been known in most of the families. The Caryophyllaceae is strikingly different in lacking betalains and having anthocyanins.
However, both betacyanins and anthocyanins are noted in the flowers of a species of Mesembryanthemum. But “no individual plant, and indeed no genus or even family of plants, has yet been found to contain both betacyanins and anthocyanins… plants which have betalains instead of anthocyanins commonly have various other flavonoid compounds, and specifically that anthoxanthins and betaxanthins often occur together. Therefore the betalain taxa evidently have most of the genetic mechanism necessary for the production of anthocyanins”.
According to Kendrick and Hillman (1971), all three members of the Centrospermae— Amaranthus caudatus, Mirabilis jalapa and Spinacia oleracea—are devoid of the phytochrome darkreversion process typical of other dicotyledons. In monocotyledons, dark reversion is lacking. Members of the Amaranthaceae, Chenopodiaceae and Portulacaceae resemble certain tropical grasses by virtue of the C4-dicarboxylic acid photosynthetic route.
Though carbon dioxide compensation points are indicative of C4 plants, they occur only in the Centrospermae and Geraniales. Such close connection with monocots are rather unlikely, but the Centrospermae contains distinct primitive plants which may be linked to the ancestral stock from which both dicots and monocots originated. In fact, Meeuse (1963) conjectured an origin of true Centrospermae from the Bennettitales by the use of morphological evidence.
The newer definition of the Centrospermae differs from the old in excluding the Molluginaceae and Caryophyllaceae which possess anthocyanins and lack betalains and in including the Cactaceae which has usually been placed in a separate order but which is found to contain betalains.
While the exclusion of the Molluginaceae and Caryophyllaceae directly contradicts the anatomical evidence, the structural data do not argue strongly against the inclusion of the Cactaceae.
This clash of orthodox and chemical evidence is augmented by the discovery of the ultrastructural characters of the sieve tube plastids. Sieve tube plastids of the Centrospermae as well as the Molluginaceae and Caryophyllaceae are characterised by peripheral ring-shaped bundles of proteinaceous filaments.
These inclusions are absent from the Polygonaceae, Plumbaginaceae and Batidaceae. Though the sieve tube evidence correlate fully with the traditional diagnostic features of the Centrospermae, they do less with the betalain distribution. The Cactaceae, Caryophyllaceae and Molluginaceae are correctly assigned to the Centrospermae.
A compromise classification has been proposed by Behnke and Turner (1971), replacing essentially the Centrospermae by two closely related orders—the Caryophyllales sensu stricto (without betalains) and the Chenopodiales (with betalains), both coming under the subclass Caryophyllidae.
Rendle suggested that the Centrospermae indicates a passage from the monochlamydeous to the dichlamydeous type of flower. The simpler forms show a floral structure similar to the Urticales and elaborate forms a floral plan similar to the Ranales. The Cactales, according to Mitra (1974), forms a connecting link between the caryophyllaceaous members on the hand and the ranalian members on the other.
Considerable evidence has been adduced favouring a connection between the Caryophyllales and Ranunculales. “Among the Caryophyllales the closest links with the Ranunculales are shown by the primitive family Phytolaccaceae which has many features that bring it near the families Menispermaceae and Lardiza balaceae. We find within it forms with apocarpous gynoecia—such as Anisomeria, Ercilla and Phytolacca subg. Pircunia—which at once connect it with the Ranunculales. But affinity with the Ranunculales is shown by the presence not only of apocarpous gynoecia but also of tricolpate pollen grains of the ranunculalean type, with its characteristic granulate surface of the middle part of the aperture membrane. The presence of the curved embryo in the Phytolaccaceae and other Caryophyllales points to an affinity with the Menispermaceae. Stipules are sometimes found in the Caryophyllales, but they are also known in some Menispermaceae and the secondary thickening from successive cambia (concentric type) of the stem of many Caryophyllales is also reminiscent of the Menispermaceae. Affinity with the Ranunculales is further corroborated by biochemical data—the presence of isoquinoline derivatives in the Chenopodiaceae and Cactaceae.”
The Centrospermales, according to Rendle, is a natural taxon. Here one encounters diversity in the differentiation of floral envelope coupled with the uniform features of placenta, ovule and embryo. Within the Phytolaccaceae, there are both monochlamydeous (Microtea) and dichlamydeous forms (Limeum) as well as forms with multiplicity of stamens and carpels.
Such a variety has led to concept that the families of the Centrospermales owe their origin to the Phytolaccaceae by development along various lines. On the basis of this concept, the Amaranthaceae and Chenopodiaceae represent a variant of the simple floral plan.
The type with two staminal whorls and two carpellary whorls has given rise to the taxa with more highly developed flowers:
If, from the original type, the inner whorl of stamens and a whorl of carpels disappear, with the consequent reduction in pistil and formation of a petaloid perianth, something like the floral structure of the Nyctaginaceae would result. One can trace the same point of origin for the simpler types of flower of the Aizoaceae like Mollugo and Sesuvium.
In more elaborate type of the Aizoaceae, as in Mesembryanthemum, the staminal whorl splits to form a series of petaloid structures and stamens. From the same source, the Portulacaceae may appear by the formation of a pair of bracteoles to constitute the dimerous calyx and by the extinction of the carpellary whorls. A further elaboration is noticed in the floral plan of the Caryophyllaceae where the alternate position of five carpels may be due to the disappearance of one or other of the two whorls in the phytolaccaceous ancestor.
Division # 2. Polypetalae:
The Polypetalae may be regarded as an assortment of orders and families numbering 12 and 82 respectively. Here the petals are free in the flower.
Order 14:
Cactales:
This is a monotypic order with the characters of its single family, the Cactaceae.
Order 15. Ranales:
The Ranales is a natural taxon. Here the floral parts are many and distinct, being spirally arranged. In general, the perianth is not differentiated into calyx and corolla. Both the stamens and carpels are free and numerous.
The Ranales, as suggested by many workers, represents the most primitive dicotyledon. From such a stock, angiospermic orders arose in various directions. The primitiveness of the order is ascribed to the presence of simple and pinnately veined leaves, unilacunar node, vessel-less wood and spiral to spirocyclic arrangement of floral parts.
That the Ranales is a heterogenous group has also been recognised. The structure of the seed coat is so different in the Annonaceae, Berberidaceae, Magnoliaceae, Myristicaceae, Nymphaeaceae, Ranunculaceae and Lauraceae that the Ranales is considered by Corner (1953) as a grade of families at the level of apocarpy and polypetaly and not a phyletic series.
According to Benzing (1967a), the diversity in protoxylem patterns in woody ranalian families is partly a reflection of the extreme evolutionary divergence of the families. This recognition has led to the fragmentation of the group into smaller orders by Hutchinson (1959) and Takhtajan (1969). Some of the newer families arising from this break up have been assigned to orders somewhat different from those of the parent families, as in the Berberidaceae and Nymphaeaceae.
In connection with heterogeneity, another problem to be sorted out is the question of interpretation of the phylogeny of the respective families. Bailey (1954) suggested that the inter-relationships of the families are of a reticulate pattern. Sastry (1969) opined that it would be impossible to arrange them in a linear sequence.
Two major factors can possibly be held responsible for the absence of linear relationships:
(a) Most of the connecting links are missing in the existing flora and fossil studies have been of little help and
(b) The families are polyphyletic.
Although the concept of the origin of flowering plants has been gaining momentum, any attempt to define the number and probable course of phyletic lines involved is bound to be speculative at the present state of our knowledge. Nevertheless, it would be worthwhile to examine some efforts in this direction.
Modern palynological evidence seems to corroborate Hutchinson’s division into woody and herbaceous series, characterised by monocolpate, derived dicolpate or acolpate pollen grains and tricolpate or modified forms respectively.
On the basis of nodal anatomy, Money et al. (1950), classified the woody families with ethreal oil cells and monocolpate or derived dicolpate, polyporatc or acolpate pollen into two groups (Table 6). A comparison of the floral morphological, embryological and seed characters of the two groups is set in Table 7.
Contrary to the view of Bailey (1956), the unilacunar node in more primitive than the tri- and multilacunar and the families of the second group are usually more primitive. Interpretation of palaeobotanical and anatomical evidence indicate that the older argument of the primitive nature of the trilacunar condition may still hold water.
The first seven families belonging to the unilacunar group roughly correspond to the Laurales of Hutchinson (1959). Within this homogenous group, more than one line of evolution is apparent. Though the Calycanthaceae and Chloranthaceae show some resemblances to other members of the group, they differ in several points and may represent independent phyletic lines.
Among the ranalian families of the trilacunar group, the Myristicaceae stands out prominently by the possession of unusual floral character, successive division of pollen mother cells and nuclear endosperm. Likewise, the Eupomatiaceae is quite distinct from the others. When the totality of evidence is superimposed on the classificatory scheme based on wood anatomy, some taxa will obviously be left out. This led Sastry (1969) to suggest that neither of the unilacunar and trilacunar groups can be regarded a single phyletic series.
Eames (1961) envisaged five main lines in the group: cabombaceous, magnoliaceous, monimiaceous, ranunculaceous and winteraceous. He also believed that there might be several others represented by single isolated families.
However, none of the above lines necessarily forms a homogenous group. The question of further splitting them can be decided only when more complete data are forthcoming. At the present moment, the phylogeny of the other families is more hazardous to guess.
Whereas some of them might fit well into one of the four major lines, others probably constitute independent lines. Though phylogenetic implications are obvious for a break up into smaller orders, the order Ranales (sensu lato) might be retained on grounds of practical expediency.
Order 16. Rhoeadales:
In Engler’s arrangement, the Rhoeadales contained five suborders and seven families: Rhoeadineae (Papaveraceae), Capparidineae (Capparidaceae, Cruciferae, Tovariaceae), Resedineae (Resedaceae), Moringineae (Moringaceae), Bretschneiderineae (Bretschneideraceaej. Within this order, Rendle included four families like the Papaveraceae, Capparidaceae, Cruciferae and Resedaceae.
Both Lawrence and Core raised the number of taxa to six by also accommodating the Fumariaceae and Moringaceae. Hutchinson split up the whole order into four groups, viz. Capparidales (Capparidaceae, Moringaceae, Tovariaceae), Rhoeadales (Papaveraceae, Fumariaceae), Cruciales (Cruciferae) and Resedales (Resedaceae). Like other workers, the present author considers the position of the order after the Ranales and before the Sarraceniales.
The Rhoeadales forms a natural group, arising from the Ranales or a ranalian ancestor traceable to Platystemon of the Papaveraceae. Hallier suggested the origin of the Cruciferae and Capparidaceae from the Berberidaceae and of the Papaveraceae, along with the Nymphaeaceae, from the Ranunculaceae. Mitra (1974) stated that the evolution of the Rhoeadales took place along different lines from the ranalian plexus.
Among the members of the Rhoeadales, the Resedaceae and Capparidaceae are regarded by Norris (1941) as the most primitive. He further noted that the Cruciferae, Fumariaceae and Papaveraceae arose “by subsequent parallel evolution from a common ancestral group somewhat resembling the existing Resedaceae and Capparidaceae”.
The gynoecium of the rhoeadalean flower in general and of the crucifer flower in particular has been a topic for speculation. Some believed it to be bicarpellary. Others accepted it as tetracarpellary. Still a few took it to be hexacarpellary. Puri (1951) remarked that the problem here “does not concern the number of carpels; rather it is a matter of placentation”.
He expressed the view that the parietal placentation in the Capparidaceae, Cruciferae, Moringaceae, Papaveraceae, Passifloraceae and possibly other families originated from the axile condition. During the course of evolution, the carpellary margins receded to the periphery. The marginal bundles or their products of fusion retained their inverse orientation, thereby producing inverted placental strands. Hence, there are only two carpels in the crucifer gynoecium.
The presence of isorhamnetin in several members of the Capparidaceae appears to be phylogenetically significant. Isorhamnetin is supposedly a characteristic compound of the Cruciferae, indicating thereby a close affinity between this family and the Capparidaceae. The alkaloid, brassicines, reported from Brassica, Lepidium and Sinapis, also exists in Cleome and Gynandropsis. The Capparidaceae is thus grouped with other thio-glucoside containing families like the Cruciferae, Moringaceae and Resedaceae under the order Rhoeadales.
The Rhoeadales is distinguished by the herbaceous habit, bisexual and hypogynous flowers with cyclic perianth segments and androecium, syncarpous pistil with two to many carpels and parietal placentation.
Order 17. Sarraceniales:
The order includes generally damp-loving herbaceous plants, having their leaves usually variously modified for trapping insects. Here the flowers are regular with an uniseriate or a biseriate perianth.
Order 18. Rosales:
Bessey suggested the Rosales as a fairly primitive taxon, being a direct descent from the Ranales. Hallier opined that the Dilleniaceae gave rise to the Rosales directly. Hutchinson supported the origin of woody Rosales from the Magnoliales via the Dilleniales. The Rosales, according to Rende, is a very natural group connected by transitional forms in which there is a passage from actinomorphy to zygomorphy and hypopyny to perigyny. The Byblidaceae and Cephalotaceae are remarkable in that they comprise insectivorous plants. The Podostemonaceae is unique for the striking adaptations to life in rushing water.
In the Rosales, the ovary is surrounded by an androperianth tube.
The taxon is large and diversified, as will be evident from the number of families treated under it by the following systematists:
Engler & Diels:
Saxifragineae (Crassulaceae. Cephalotaceae, Pittosporaceae, Byblidaceae, Brunelliaceae, Cunoniaceae, Myrothamnaceae, Bruniaceae, Roridulaceae, Eucommiaceae), Rosineae, (Platanaceae, Crossosomataceae, Rosaceae, Connaraceae (Leguminosae).
Rendle:
Crassulaceae, Saxifragaceae, Cunoniaceae, Pittosporaceae, Podostemonaceae, Hydrostachyaceae, Hamamelidaceae, Platanaceae, Rosaceae, Connaraceae. Leguminosae.
Lawrence:
Crassulaceae, Saxifragaceae, Pittosporaceae, Cunoniaceae, Hamamelidaceae, Eucommiaceae, Platanaceae, Crossosomataceae, Rosaceae, Leguminosae.
Core:
Podostemonaceae, Crassulaceae, Cephalotaceae, Saxifragaceae, Pittosporaceae, Cunoniaceae. Hamamelidaceae, Platanaceae, Rosaceae, Connaraceae, Leguminosae.
Hutchinson:
Rasaceae, Dichapetalaceae, Calycanthaceae.
Mitra:
Rosaceae, Saxifragaceae, Crassulaceae, Cunoniaceae, Pittosporaceae, Connaraceae, Leguminosae.
Cronquist:
Eucryphiaceae, Cunoniaceae, Davidsoniaceae, Pittosporaceae, Byblidaceae, Columelliaceae, Hydrangeaceae, Grossulariaceae, Bruniaceae, Alseuosmiaceae, Crassulaceae, Cephalotaceae, Saxifragaceae, Rosaceae, Neuradaceae, Chrysobalanaceae, Leguminosae.
The present author largely accepts Mitra’s concept of the Rosales, but includes the Podostemonaceae within its scope.
Order 19. Parietales:
Usually regarded as an artificial assemblage, the Parietales is a large taxon. Here the families are variously redistributed by systematists: 31 by Engler and Diels, 22 by Lawrence and Core and 10 by Rendle. The presence of parietal placentation is almost a constant character.
Order 20. Malvales:
The Malvales is a natural group. This is indicated by the presence of stellate and mucilage cells or canals. The flowers are generally bisexual, regular, hypogynous and pentacyclic. The calyx is valvate. The stamens are usually many and united into a column; hence the taxon was named Columniferae by Eichler. The placentation is axile.
Bessey assumed that the Malvales originated from the Ranales via the Resales. Hallier opined that the Ranales was the direct ancestor of the Malvales. Some botanists also believed that the Guttiferales gave rise to the Malvales.
The order is related to the Guttiferae by the regular hypogynous flowers with pentamerous calyx, corolla and by the androecium which indicates a tendency to connation of parts. The Malvales forges a link with the Euphorbiaceae due to the frequent occurrence of branched multicellular hairs and ovary structure which often separates the one seeded parts in the fruit; an endotropic course of the pollen tube is common to both groups. The Bombacaceae resembles the Paeoniaceae (Ranunculaceae) as far as centrifugal development and trunk-vascular supply of stamens are concerned.
Engler and Diels conceived the Malvales as made up of four suborders and seven families: Elaeocarpineae (Elaeocarpaceae), Chlaeneae (Chalaenaceae), Malvineae (Tiliaceae, Malvaceae, Bombacaceae, Sterculiaceae), Scytopetalineae (Scytopetalaceae). Gunderson (1950) and Benson (1957) followed the Englerian concept with reference to the order. Bessey expanded the order to incorporate into it also the Balanopsidaceae, Ulmaceae, Moraceae and Urticaceae.
Bentham-Hooker included the Elaeocarpaceae Tiliaceae and Bombacaceae in the Malvaceae. The Malvales formed Rendle’s seventh order in the Dialypetalae after the Guttiferales and before the Tricoccae. Both Lawrence and Core treated the Malvales as containing five families (Elaeocarpaceae, Tiliaceae, Malvaceae, Sterculiaceae, Bombaceae). Hutchinson (1959) split up the order into the Tiliales (which comprises the Dirachmaceae, Scytopetalaceae, Tiliaceae, Sterculiaceae, Peridiscaceae, Bombacaceae) and Malvales (which embraces the Malvaceae).
Order 21. Geraniales:
The order is closely related to the Malvales, from which is differentiated by the typically obdiplostemonous androecium and prevalence of herbaceous forms. Generally, the stamens are twice as many as sepals. The ovules are pendulous with an upwardly-directing micropyle and a dorsal raphe. The styles are often persistent in the fruit. The seeds are without any endosperm.
Engler and Diels treated the order as composed of six suborders and 21 families: Geraniieae (Oxalidaceae, Geraniaceae, Tropaeolaceae. Linaceae, Erythroxylaceae, Zygophyllaceae, Cneoraceae, Rutaceae, Simaroubaceae, Burseraceae, Meliaceae, Akariaceae), Malpighiineae (Malpighiaceae, Trigoniaceae, Vochysiaceae), Polygalineae (Tremandraceae, Polygalaceae), Dichapetalineae, (Dichapetalaceae) Tricoccae (Euphorbiaceae, Daphniphyllaceae), Callitrichineae Callitrichaceae).
Bessey accommodated all these families in the Geraniales. Hallier. Wettstein and Rendle regarded them to cover three orders. Hutchinson distributed some of the families of the Geraniales among four orders (Geraniales, Rutales, Meliales, Malpighiales) and several other families among five other orders.
Evidence from different branches of botany show that the Geraniales, as constructed by Engler, is not a natural group. On the other hand, the order is accepted as composed of somewhat four or five disjunctive taxa.
Order 22. Sapindales:
The order is closely related to the Geraniales from which it differs in having ovules pendulous with a ventral raphe and downward microphyle or ovules erect with a ventral raphe and upward microphyle.
According to Engler and Diels, the Sapindales is made up of 11 suborders and 23 families:
Buxineae (Buxaceae), Empetrineae (Empetraceae), Coriarineae (Coriariaceae), Limnanthineae (Limnanthaceae), Anacardiineae (Anacardiaceae), Celastrineae (Cyrillaceae, Pentaphyllaceae. Corynocarpaceae, Aquifoliaceae, Hippocrataceae, Salvadoraceae, Stackhousiaceae, Staphyleaceae), Icacineae (Icacinaceae, Celastraceae, Atoxiaceae, Hippocastanaceae, Sapindaceae), Sabiineae (Sabiaceae), Melianthineae (Melianthaceae), Didiereineae (Didiereaceae) and Balsamineae (Balsaminaceae).
All other systematists have considered the families of the Sapindales to belong in from three to six orders. There is a general agreement that the Sapindales should contain such families as the Sapindaceae, Hippocastanaceae, Sabiaceae, Melianthaceae. Aceraceae and Anacardiaceae, while the Celastraceae, Aquifoliaceae and Hippocrataceae should be accommodated in the Celastrales.
Order 23. Rhamnales:
In the Rhamnales, the plants are usually woody. Here the flowers are unisexual or apetalous or both.
The order differs from other polypetalous taxa in having a low stamen number and ovary subtended or surrounded by a disc. It is distinguished from the Geraniales and Sapindales in the presence of stamens in a single whorl, as many as the sepals and opposite to the petals.
Engler and Diels treated the Rhamnales as compound of two families: Rhamnaceae and Vitaceae. Bessey included these families in the Celastrales. Wettstein and Hallier placed these families under a separate order (Rhamnales), which indicated a relationship with the Rosales.
According to Rendle, the Celastrales and Rhamnales constitute a parallel series derived from some diplostemonous type resembling the Rutales. Gundersen supported Bessey’s contention from cytological aspects. Hutchinson accepted the order Rhamnales, but added two more families like the Elaeagnaceae and Heteropyxidaceae. Benson agreed with the concept of the Rhamnales as put forward by Engler.
The families of the Rhamnales, according to Core (1955), can be recognised by the following characters:
(1) Trees, shrubs or lianas; fruit a drupe – Rhamnaceae
(1) Climbing shrubs; fruit a berry – Vitaceae
The order is closely allied to the Rosales and Umbellales. This is a natural taxon with a transition from the perigyny to epigyny. Here the flowers are bisexual and polypetalous, perianth tetramerous, placentation axile and style simple. Another characteristic feature is the presence of intraxylary phloem in the stem.
The Myrtiflorae of Engler and Diels was made up of four suborders and 23 families: Thymelaeineae (Geissolomataceae, Peneaceae, Oliniaceae, Thymelaeaceae, Elaeagnaceae), Myrtineae (Lythraceae, Heteropyxidceae, Sonneratiaceae, Crypteroniaceae, Punicaceae, Lecythidaceae, Rhizophoraceae, Nyssaceae, Alangiaceae, Combretaceae, Myrtaceae, Melastomaceae, Hydrocaryaceae, Onagraceae, Haloragaceae), Hippuridineae (Hippuridaceae, Thelygonaceae), Cynomorineae (Cynomoriaceae).
Wettstein accepted the order with a slight modification by merging the Hydrocaryaceae with the Onagraceae and separating the Gunneraceae as distinct from the Haloragaceae. Bessey also accepted the concept, but transferred the Thymelaeineae to the Celastrales and retained the Nyssaceae in the Cornaceae (under the Umbelliferae).
Rendle adopted the Engler treatment, but interpreted the Nyssaceae and Alangiaceae as separate taxa of the Umbelliflorae. Hallier removed the Thymelaeineae to the Daphnales, the Alangiaceae to the Santalales and the Onagraceae to the Ranales. He restricted the order Myrtines for such families as the Lythraceae, Lecythidaceae, Rhizophoraceae, Combretaceae, Myrtaceae and Melastomaceae.
Hutchinson distributed the various families among five orders: the Aquilariaceae and Thymelaeaceae in the Thymelaeales, the Elaeagnaceae and Heteropyxidaceae in the Rhamnales, the Lythrales in the Araliales and the Myrtaceae, Lecythidaceae, Sonneratiaceae, Punicaceae, Combretaceae and Melastomaceae in the Myrtales. After a study of Geissoloma marginatum, Dahlgren and Rao (1959) questioned the inclusion of the Geissolomataceae in the Myrtales.
They emphasised its similarity with the Cleaceae and Salvadoraceae. Bhatnagar (1963) suggested the separation of Duabanga and Sonneratia from the Lythraceae. He felt that the Lythraceae and Onagraceae did not resemble much in their floral vasculature and that they could only tentatively be retained in the Myrtales. On the basis of floral anatomy, Gupta (1962) supported the transference of Barringtonia, Careya and Couroupita to a separate family Lecythidaceae.
While Lawrence considered 14 families in the Myrtiflorae and Cronquist 13 in the Myrtales, Core mentioned 12 families in the order. Core’s notion is followed here, but the sequence of the families has been changed.
Order 25. Umbellales:
The Umbellales is a natural taxon. It is characterised by a tendency of the flowers to be in umbels, great reduction in the calyx associated with epigyny, single whorl of stamens and presence of two uniovulate carpels.
Engler and associates conceived the order as composed of three families: Araliaceae, Umbelliferae, Cornaceae. Though the circumscription of the order was adopted by Rendle, it was not accepted in toto by Bessey and Wettstein. Bessey treated both Garrya and Nyssa within the concept of the Cornaceae. Wettstein expanded the order to accommodate the Garryaceae.
However, Hallier recognised two families: Cornaceae, Umbelliferae; here the Araliaceae was merged with the Umbelliferae. Rickett (1945) created two orders, the Umbellales for the Araliaceae and Umbelliferae and the Cornales for the Cornaceae and Nyssaceae.
Revising his earlier views, Hutchinson (1948) constructed the Umbellales for the Umbelliferae only, considered the Cornaceae within the Cunoniales (which is a derivative of the Rosales) and set up the Araliaceae as a distinct taxon (Araliales) originating from the Cornaceae. He also regarded the Umbellales as a climax group, possibly derived from the Saxifragales stock and parallel with the Araliaceae.
While the Araliaceae and Umbelliferae are closely related, the Cornaceae stands somewhat alone. The secretory passages of the first two families are rarely present in the third. Moreover, the leaves are generally opposite, carpel number less constant and micropylar position varies in the Cornaceae.
The family indicates remarkable similarities with the tribe Sambuceae of the sympetalous family Caprifoliaceae from which it differs only by the union of petals. The first two families bear relationship with the Celastrales and Rhamnales in respect of the small size of flowers, single staminal whorl conspicuous disc and uniovulate ovary.
However, the position of the ovule is different and the stamens are opposite to the petals. Whereas the Umbellales may be considered as an ally of these taxa, it represents a further line of development in the direction of epigyny accompanied by the aggregation of the inconspicuous flowers. This tendency to aggregation of flowers is a biological factor of prime importance in insect pollination which finds its most complete expression in the Compositae. The probable phylogeny of the Umbellales may be traced from the Rosales.
“The true relationships of the Umbellales appear to be with the Sapindales, in which compound leaves, stipules, multilacunar nodes, trinucleate pollen, schizogenous secretory canals, vasicentric parenchyma, vessels with a single terminal pore, and a centrally vasculated gynoecium are well known. If the Araliaceae had the ovary superior instead of inferior they would be perfectly at home in the Sapindales. Anatomically they compare well with the Burseraceae except in having somewhat wider wood rays. The width of the rays probably reflects the tendency toward herbaceousness which begins in the Araliaceae and culminates in the Umbelliferae”.
Division # 3. Sympetalae:
The Sympetalae is a combination of orders and families numbering eight and 45 respectively. Here the flowers show a greater or less union of the petals.
Order 26. Ericales:
According to many systematists, the Ericales is a primitive component of the Sympetalae and forms a connecting link between the Archichlamydeae and Metachlamydeae. The primitiveness of the group is indicated by the retention of the polypetalous characters in some of its members. Bessey viewed the origin of the order from the Geraniales. Hallier derived it from the Guttiferales. Hutchinson interpreted it as arising from his Theales.
The Ericales is a natural taxon. It is characterised by the usually pentamerous and actinomorphic flowers. Here the petals are both united and free. The androecium is obdiplostemonous and inserted at the edge of a hypogynous nectariferous disc. The pollen grains are often in tetrads. The placentation is axile and the ovules are unitegmic and numerous.
Engler and Diels conceived the Ericales to be made up of two suborders and four families- Ericineae (Clethraceae, Pyrolaceae, Ericaceae), Epacridineae (Epacridaceae). Rendle considered five families (Clethraceae, Ericaceae, Pyrolaceae, Epacridaceae, Diapensiaceae) in the order. Lawrence adopted Engler’s concept of the order and Mitra supported Rendle’s idea.
In the order, Core accommodated six such families as the Clethraceae, Pyrolaceae, Lennoaceae, Ericaceae, Epacridaceae and Diapensiaceae. Cronquist included seven families in the order- Cyrillaceae, Clethraceae, Ericaceae, Epacridaceae, Empetraceae, Pyrolaceae, Monotropaceae. Hutchinson raised the number of families in the order to eight by creating more families like the Monotropaceae and Vacciniaceae.
Order 27. Primulales:
The Primulales is a natural taxon. It is characterised by the pentamerous flowers, single whorl of stamens opposite to the petals, ovary superior with free central placentation and ovules with two integuments.
The prevalence of pentamery, unilocular ovary with free central placentation and seeds with a copious endosperm indicate a connection of the Primulales with the Centrospermales. It has been assumed that the order originated from a dialypetalous stock allied to that from which the Centrospermales sprang.
Bessey placed the Plumbaginaceae and Plantaginaceae in his Primulales. Hallier set up the Primulales near his Bicornes, deriving it from the Ochnaceae of his Guttales. Similar circumscription was made by Wettstein who regarded the Primulales as related to the Ericales (Bicornes).
The order, according to Rendle, Lawrence and Cronquist, contains three families: Theophrastaceae, Myrsinaceae, Primulaceae. Core grouped the Myrsinaceae, Plumbaginaceae and Primulaceae into two orders: the Primulales comprising the Primulaceae and Plumbaginaceae and the Myrsinales covering the Myrsinaceae.
Order 28. Ebenales:
The Ebenales, according to Hallier, is not a natural taxon. It bears no relationship with the pentacyclic orders. It may be that the order had a distinct origin from the Dialypetalae. Bessey suggested that the Geraniales gave rise to both Ericales and Ebenales along parallel lines.
Wettstein sought a possible link with the Malvales, Geraniales and Rutales which are characterised by the diplostemonous androecium having a tendency to indefinite stamens and septate isomerous gynoecium with an axile placentation. Copeland (1938) stated that “the Theaceae … most nearly represent the ancestry of the Ebenales”. Hutchinson opined that the order evolved from the Magnohales through the Dilleniales and Bixales.
The Ebenales is distinguished by the woody habit, actinomorphic and hypogynous flowers, gamopetalous corolla, epipetalous stamens in two to three whorls and ovary basically septate with one to two ovules in each loculus.
Engler and Diels considered the order as composed of two suborders and seven families- Sapotineae (Sapotaceae, Hoplestigmataceae), Diospyrineae (Ebenaceae, Diclindantheraceae, Symplocaceae, Styracaceae, Lissocarpaceae). Hallier treated the Sapotaceae in his Sapotales and the Ebenaceae and Styracaceae in his Santalales. Hutchinson followed a different view by placing the families of the Styracales and Ebenales apart from each other. Cronquist included five families in the order, viz. Sapotaceae, Ebenaceae, Styracaceae, Lissocarpaceae, Symplocaceae.
Order 29. Gentianales:
The Gentianales (which is equivalent to the Contortae of some and the Loganiales of others) is a natural taxon. This is reflected in the nature of aestivation, structure of calyx and number of carpels. As a matter of fact, the plants bear opposite or pinnately compound leaves. The flowers are actinomorphic and have two carpels. The corolla is gamopetalous, the lobes being usually convolute. The stamens are adnate to or near the corolla base.
Engler and Diels conceived the Contortae to contain two suborders and six families: Oleineae (Oleaceae), Gentianeae (Desfontaineaceae, Loganiaceae, Gentianaceae, Apocynaceae, Asclepiadaceae). Bessey suggested that the Gentianales arose from the Geraniales which separated into two phyletic lines, one giving rise to the Loganiales and the other to the Polemoniales.
Hallier interpreted the origin of the Loganiales from the Linaceae of his Guttales and placed all the families of the Contortae under the Tubiflorae. Wettstein as well as Rendle “restricted the Contortae to contain only the suborder Gentianineae and segregated the Oleineae as the Oleales, considering the latter to have been derived from stocks allied to the Staphyleaceae and the former to be advanced over the Tubiflorae”.
Hutchinson split up the Gentianales into three large taxa- Loganiales (Potaliaceae, Loganiaceae, Buddleiaceae, Antoniaceae, Spigeliaceae, Strychnaceae, Oleaceae), Apocynales (Plocospermaceae, Apocynaceae, Periplocaceae, Asclepiadaceae), Gentianales (Gentianaceae, Menyanthaceae).
Order 30. Tubiflorales:
The order is a natural taxon. Here the plants are herbaceous with regular or irregular tetracyclic flowers, gamopetalous corolla, hypogynous and epipetalous stamens and unitegmic ovules.
Engler and Diels set up the order to contain eight suborders and 22 families: Convolvulineae (Convolvulaceae, Polemoniaceae, Fouqueriaceae), Lennonineae (Lennoaceae), Boragineae (Hydrophyllaceae, Boraginaceae), Verbenineae (Verbenaceae, Labiatae), Solanineae (Nolanaceae, Solanaceae, Scrophulariaceae, Bignoniaceae, Pedaliaceae, Martyniaceae, Orobanchaceae, Gesneriaceae, Columelliaceae, Lentibulariaceae, Globulariaceae), Acanthineae (Acanthaceae), Myoporineae (Myoporaceae), Phrymineae (Phrymaceae).
Wettstein did likewise except that the Fouqueriaceae was removed to the Parietales and that the Plantaginaceae was accommodated in the order. Rendle also followed Engler’s circumscription, but the Convolvulaceae was segregated as the Convolvulales, the Fouqueriaceae and Lennoaceae omitted and the Selaginaceae created.
Lawrence treated all the families in the order, but excluded the Columelliaceae. Core considered all these families under the order, but placed the Fouqueriaceae within the Parietales and Lennoaceae within the Ericales.
Hutchinson split up the entire order into seven taxa; under the Lignosae, Bignoniales (Cobaeaceae, Bignoniaceae, Pedaliaceae, Martyniaceae) and Verbenales (Ehretiaceae, Verbenaceae, Stilbeaceae, Chloanthaceae, Phrymaceae) and under the Herbacae, Solanales (Solanaceae, Convolvulaceae, Nolanaceae), Personales (Scrophulariaceae, Acanthaceae, Gesneriaceae, Orobanchaceae, Lentibulariaceae, Columelliaceae), Polemoniales (Polemoniaceae, Hydrophyllaceae, Cuscutaceae), Boraginales (Boraginaceae) and Lamiales (Myoporaceae, Selaginaceae, Globulariaceae, Labiatae).
To trace a point of origin for the Tubiflorales among polypetalous dicots is fraught with difficulty. The order, according to Rendle, arose from a stock characterised by pentamerous flowers, oligomerous gynoecium, numerous marginal ovules and disc development below the ovary.
Wettstein envisaged a type close to the Rosales in which sympetaly is of occasional incidence. For example, the Saxifragaceae resembles the Solanaceae or Scrophulariaceae on the basis of bilocular ovary with numerous anatropous ovules on large placentae.
The Tubiflorales is a large group, illustrating several lines of floral development. In the Convolvulaceae, the flowers are actinomorphic with ovary bilocular having two ovules in each loculus or tetralocular having one ovule in each loculus. It is related to the Polemoniaceae, but differs from it by the terminal style and ovary structure. The flowers of the Polemoniaceae tend to be slightly zygomorphic, but the carpels may be two, three or five and ovules few to many in each loculus.
The floral plan of the Hydrophyllaceae is similar to that of the Polemoniaceae, except that the ovary is bicarpellary and bilocular or unilocular due to the failure of the large marginal placentae to meet in the centre.
Although in the Boraginaceae the flowers are zygomorphic, the originally bilocular ovary is divided into four one- ovuled portions by a later formed septum. Zygomorphy does not extend to the calyx in the Verbenaceae where the corolla is somewhat two-lipped. The calyx is sometimes regular in the Labiatae, but it is prominently two-lipped.
The two carpels of the Verbenaceae unite to form an originally bilocular ovary; each loculus contains two ovules and is later divided by a partition into one-ovuled parts. The reduction and specialisation of the ovary is complete in the Labiatae where the bilocular ovary is divided into four one-ovuled chambers.
The Solanaceae is recognised by the usually regular isostemonous flowers and bicarpellary generally bilocular ovary with numerous ovules. With four or two fertile stamens and often somewhat zygomorphic flowers, the tribe Salpiglossideae forms a connecting link with the Scrophulariaceae where the zygomorphy of the corolla and androecium is ordinarily conspicuous.
The Gesneriaceae shows a tendency towards epigyny: here the ovary is unilocular and contains numerous ovules. The Orobanchaceae also contains an unilocular many-ovuled ovary. The Lentibulariaceae has a markedly bilabiate corolla and shows a reduction in the number of stamens as well as a free central placentation in the ovary.
The floral plan of the Bignoniaceae is similar to that of the Scrophulariaceae. The Acanthaceae indicates a specialisation of the flower and fruit associated with a great variety of stamen development and a remarkable mechanism for seed dispersal.
Order 31. Plantaginales:
The order contains a single family, the Plantaginaceae.
Order 32. Rubiales
The Rubiales is a natural taxon. This is reflected in the leaves being opposite, inflorescence cymose flowers actinomorphic to zygomorphic, ovary inferior and anthers distinct.
As conceived by Engler and Diels, the Rubiales is composed of five families- Rubiaceae, Adoxaceae, Dipsacaceae, Caprifoliaceae, Valerianaceae. This circumscription was also accepted by Rendle, Gundersen, Core and Benson. However, Lawrence did not account for the Adoxaceae. Hutchinson accepted the Rubiales to contain the Dialypetalanthaceae and Rubiaceae.
He created the Valerianales in order to accommodate the Valerianaceae, Dispacaceae and Calyceraceae. He removed the Adoxaceae to the Saxifragales and the Caprifoliaceae to the Araliales. Porter included the Rubiaceae and Caprifoliaceae in the Rubiales and placed the Adoxaceae, Dipsacaceae, Calyceraceae and Asteraceae (Compositae) under the Asterales. Cronquist retained the Rubiaceae in the Rubiales, but transferred the Caprifoliaceae, Adoxaceae, Valerianaceae, Dipsacaceae and Calyceraceae to the Dipsacales.
A perusal of the characters of the Umbellales, Rubiales and Campanulales points out that the three taxa are closely related.
These characters include:
(i) A shift from the woody arboreal habit to the herbaceous one;
(ii) A reduction in the number of floral parts associated with an increasing tendency to zygomorphy;
(iii) An occurrence of epigynous flowers and epigynous disc;
(iv) A tendency to attain conspicuousness by the aggregation of flowers into umbels, cymose umbels and capitate inflorescences;
(v) A loss of the protective function of the calyx and its development into pappus and scales as organs for the distribution of fruits, seeds and
(vi) The presence of a bicarpellary ovary which tends to abort all but one of the loculi, resulting in the development of a few- or one-seeded fruits.
The origin of the Rubiales, according to Rendle, can be traced among the epigynous tetracyclic Dialypetalae. In fact, the order may be considered as a sympetalous development of a stock akin to the Umbelliflorae. Moreover, a comparison of the genera of the Rubiaceae and Caprifoliaceae with the Cornaceae reveals a close connection.
Only the polypetalous feature of the Cornaceae seems to make the family distinct; otherwise, the three taxa look exactly alike. Hutchinson (1959), however, derived the Rubiales from loganiaceous ancestors and the Valerianales from the Saxifragales stock.
Order 33. Campanulales:
The order is distinguished by the epigynous flowers, connate or coherent stamens, bithecal anthers and inferior ovary.
The Campanulales, according to Rendle, is a sympetalous development of a stock akin to the Passiflorales where the flowers tend to be gamopetalous and epigynous. The origin of the order may be sought from the Rubiales and this is shown by the structure of the inflorescence.
But the cymose feature of the head in the Rubiales offers contrast with the racemose capitulum in the Campanulales. However, resemblances between the Rubiales and Campanulales may be considered as indicative of convergent evolution rather than a direct relationship.
Mitra suggested the evolution of the Campanulales from the Ranales thus:
Ranales → Rosales → Umbellales → Rubiales → Campanulales.
Engler and Diels conceived the Campanulales to have six families- Campanulaceae, Brunoniaceae, Calyceraceae, Goodeniaceae, Stylidiaceae, Compositae. Lawrence included all these families in his concept of the order. Rendle excluded the Brunoniaceae and Calyceraceae from the order. Core also ignored these two families, but made up the number to six by incorporating the Cucurbitaceae and Lobeliaceae into the order.
Hutchinson split up the entire order into five groups- Cucurbitales (Cucurbitaceae, Begoniaceae, Datiscaceae, Caricaceae), Valerianales (Valerianaceae, Dipsacaceae, Calyceraceae), Campanales (Campanulaceae, Lobeliaceae), Goodeniales (Goodeniaceae, Brunoniaceae, Stylidiaceae), Asterales (Compositae).
Cronquist distributed his families to two orders; Campanulales (Pentaphragmataceae, Sphenocleaceae. Campanulaceae. Stylidiaceae, Brunoniaceae, Goodeniaceae) and Asterales (Compositae).
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