In this article we will discuss about:- 1. General Features of the Rubiaceae 2. Floral Range in the Rubiaceae 3. Divisions 4. Position and Affinity 5. Number and Distribution 6. Commonly Occurring Plants 7. Economic Aspects.
General Features of the Rubiaceae:
Habit – Herbs, shrubs or trees.
Leaves – Opposite, simple, entire, stipulate (stipules interpetiolar).
Inflorescence – Cymes or decussate panicles, sometimes heads.
Flowers – Bisexual, regular, epigynous, 4- or 5-merous.
Calyx – Sepals 4 or 5, united.
Corolla – Petals 4 or 5, united.
Androecium – Stamens 4 or 5, epipetalous; anthers introrse.
Gynoecium – Carpels 2, connate, crowned by a fleshy disc: ovary inferior, 2-locuIar; ovules 1 or more in each loculus; style bifid or multifid.
Fruit – Berry, capsule or drupe.
Seeds – Embryo straight; endosperm fleshy, horny or cartilaginous.
Floral Range in the Rubiaceae:
The flowers are solitary in Gardenia. They may be aggregated into globose heads, as in Adina, Anthocephalus, Morinda, etc. Although flowers are generally regular, irregular flowers are also found (Henriquezia, Posoqueria). Unisexual flowers are met with in Anthospennum and Coprosma.
Variation in the calyx structure has been noted. In Mussaenda, Nematostylis and Warszewiczia, one of the sepals becomes enlarged, showy and leafy. The calyx limb is plumose in Gaillonia.
The corolla is somewhat bilabiate in Capirona, Dichilanthe and Ferdinandusa and partite to the base in Aulacodiscus. The corolla lobes are appendaged or horned (Corynanthe, Rudgea) or dextrorsely contorted (Cosmihuena, Deppea).
The stamens are declinate (Tammsia) or monadelphous (Solenandra). The filaments are very unequal in Pallasia and Remijia as well as the anthers are somewhat united in Acranthera and Neurocalyx.
The ovary is inferior, but semi-inferior in Synaptanthera and superior in Gaertnera and Pagamea. A bilocular ovary is a general rule in the family. Hamelia, Knoxia, Meyna, etc. have an unilocular ovary with a single ovule. Pavetta also represents an uniovulate condition with the ovule sunken in the fleshy funiculus.
The ovules are paired in the loculi, one pendulous and the other ascending, e.g. Scyphiphora. In Cinchona, Gardenia, Oldenlandia, Rondeletia, etc., there are many ovules in each loculus. The ovules may be attached to the base of the ovary, as in Hydnophytum, Myrmecodia, Paederia, Uragoga, etc. The ovules are also fixed to the septum in Asperula, Galium, Rubia and related genera.
Divisions of the Rubiaceae:
The Rubiaceae is divided into three subfamilies:
Subfamily I. Cinchonoideae:
Predominantly woody. Raphides absent in leaves; stipules rarely divided. Trichomes on stems and leaves without cross walls. Heterostyly absent. Seeds with endosperm. Example- Cinchona.
Subfamily II. Guettardoideae:
Woody. Raphides absent. Trichomes without cross walls.
Heterostyly absent. Seeds without endosperm. Example- Guettardia.
Subfamily III. Rubioideae:
Predominantly herbaceous. Raphides present; stipules often divided into many branches. Trichomes often with cross walls. Heterostyly common. Seeds without endosperm. Example- Rubia.
Position and Affinity of the Rubiaceae:
In Engler’s arrangement, the Rubiales appeared under the Rubiales between the Plantaginales and Cucurbitales. Bentham-Hooker included this family in the series Inferae and just before the Compositae. Hutchinson placed the family in the Rubiales after the Apocynales and before the Bignoniales.
“The Rubiaceae resembles members of the Gentianales (particularly the Loganiaceae) in having well developed stipules which often bear special glands (colleters) and in possessing certam alkaloids; on the other hand, it differs in the absence of internal phloem and in its inferior ovary. The two features are typical of the Dipsacales, but the latter tend to lack stipules and do not synthesize chemicals”.
The Rubiaceae is closely related to the Cornaceae in such features as the cymose umbel-like inflorescence, epigyny, calyx suppression, etc. It also bears a relationship with the Adoxaceae and Caprifoliaceae in the presence of inferior ovary. It establishes a link with the Compositae, since the head of the Compositae can be derived from the head-like inflorescence of some members of the Rubiaceae and Dipsacaceae.
Number and Distribution of the Rubiaceae:
There are about 500 genera and 7,000 species in the Rubiaceae. The members of this family dominate the warmer parts of the world with extensions into the temperate and frigid zones.
Commonly Occurring Plants of the Rubiaceae:
Adina cordifolia (Roxb.) Hook. f. ex Brandis is a large deciduous tree which is often buttressed.
Anthocephalus cadamba (Roxb.) Miq. is a large tree, having horizontal branches.
Borreria articularis (L. f.) F. N. Will, is a perennial herb.
Canthium angustifolium Roxb. is a spreading shrub of Sunderbans.
Dentella repens (L.) Forst., a herb found in waste places, bears white flowers.
Cape Jasmine (Gardenia jasminoides Ellis), Hamelia patens Jacq., Ixora arborea Roxb. ex Sm. and I. coccinea L. are garden plants.
Knoxia sumatrensis (Retz.) DC. is an erect annual.
Meyna laxiflora Robyns is a highly spinous tree.
Mitragyna parviflora (Roxb.) Korth. is a large pubescent or nearly glabrous tree.
Morinda citrifolia L. is a garden plant, producing multiple fruits.
Mussaenda frondosa L. is a small shrub with an interesting flower where one of the sepals develops into a large petaloid yellow leaf.
Neanotis calycina (Wall, ex Hook, f.) Lewis is a slender annual herb.
Oldenlandia biflora L., O. corymbosa L. and O. umbellata L. occur in rice fields.
Paederia scandens (Lour.) Merr. is a twining slender foetid shrub.
Pavetta indica L. is a small tree.
Petunga racemosa (Roxb.) K. Schum. is an evergreen shrub met with in the Sunderbans.
Randia spinosa Poir. is a large spinous shrub.
Indian Madder (Rubia tinctorum L.) is a climbing herb, having big stipules.
Uncaria macrophylla Wall, is a strong climber.
Wendlandia exserta (Roxb.) DC. is a small crooked tree.
Xeromphis spinosa (Thunb.) Keay is a small tree, bearing dimorphic flowers.
Economic Aspects of the Rubiaceae:
A number of plants of the Rubiaceae is grown ornamentally, e.g., Asperula, Bouvardia, Coprosma, Gardenia, Ixora, Mitchella, Nertera, Pentas, etc.
The fruits of Anthocephalus cadamba are edible; a spirit is distilled from the flowers of this plant. The seeds of Coffee arabica, C. liberica (Liberia) and C. robusta (Congo) are ground for the beverage, ‘coffee’. The ripe fruits of Randia spinosa are eaten after roasting.
The juice of Adina cordifolia is used to kill maggots in sores. The roots of Cephaelis ipecacuanha is the source of ‘vinum ipecac’. The bark of Cinchona calisaya, C. ledgeriana, C. officinalis, C. pitayensis and C. succirubra yields ‘quinine’. Oldenlandia corymbosa and O. umbellata are useful, the farmer as a febrifuge and the latter as an expectorant. The leaves of Paederia scandens form a good stomachic. Uncaria gambier (Indonesia) is the source of ‘gambier’, a resinous substance useful in medicine.
Calycophyllum candidissimum and Ixora ferrea furnish ‘lance wood’ and ‘iron wood’ respectively. Elaeagia utilis (Colombia) produces a resin, used for making paint. Some species of Galium were once employed for filling mattress due to their pleasant odour. The bark of Hymenodictyon excelsum is astringent and used for tanning.
From the bark of Mitragyna pannflora is obtained a kind of fibres for making cordage. A yellow dye, extracted from the bark of Morinda angustifolia and M. coreia, is used for dyeing carpets, turbans, etc. The roots of Rubia cordifolia serve as the source of a red dye, ‘Turkey red’, used for colouring medicinal oils.
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