In this article we will discuss about:- 1. Introduction to Dendrology 2. Application of Dendrology 3. History of Plant Classification 4. International Code of Botanical Nomenclature 5. Identification of Trees in a Tropical Forest Landscape 6. Floral Diagram and Floral Formula 7. Collection and Submission of Herbarium Specimens.
Introduction to Dendrology:
In a forest landscape, the tree is the most visible and dominant biological organism. So, one of the important and early challenges of a forestry professional is to correctly identify these organisms, at least a few of them, by its exact name and family.
The further application of the various forest skills of a forest manager primarily rests on his fundamental knowledge about plant systematics. Plant taxonomy is an easy discipline if one could master some of the basic morphological characters of the plants and use it to unravel the identity of a plant. Dendrology is the study of trees and for some, it is also the taxonomy or systematics of woody plants.
Applications of Dendrology:
The Indian subcontinent is blessed with unique geographic position, distinct physiographic, edaphic and climatic zones and gradients. This has favoured the development of a very rich and diverse flora with high percentage of endemism India is one of the top ten plant rich nations of the world and fourth among the Asian countries.
Though with only 2.5 per cent of the world’s land area, India accounts for 7.8 per cent of the recorded species of the world including 45,500 recorded species of plants. India is also considered as one of the world’s 17 “mega diverse” countries in terms of biodiversity.
India is also recognized as one of the eight Vavilovian centres of origin and diversity of crop plants, having more than 300 wild ancestors and close relatives of cultivated plants, which are still evolving under natural conditions. India has four global biodiversity hot spots (Eastern Himalaya, Indo-Burma, Western Ghats and Sri Lanka, and Sundaland).
About 27 per cent of all the species of higher plants recorded in the Indian region can be found (about 4,000 of 15,000 species) in the Western Ghats. Further, almost 1,800 species are endemic to the region. Based on the uniqueness of the phyto-geographical zones and pattern of endemism, 25 micro hot spots centres of endemic flora have also been identified in India.
The unique features of the plant diversity, among others, include 60 monotypic families and over 6,000 endemic species. It is widely believed that India also harbours over 256 globally threatened plant species. With over 16 major forest types and 251 subtypes, the total forest and tree cover is approximately 23.39 per cent of the geographical area.
This biological richness has prompted the establishment of the Botanical Survey of India, as early as in 1890. More recently in 1999, the Ministry of Environment and Forests, Government of India had launched the All India Coordinated Project on Capacity Building in Taxonomy (AICOPTAX) with the sole mission of enhancing India’s capability for inventorying, monitoring, conserving and utilizing biodiversity as well as for establishing leadership in the field of taxonomy at regional and global levels. In 2003, India also set up a National Biodiversity Authority (NBA) with an explicit mandate of conservation of biological resources and associated knowledge as well as facilitating access to them in a sustainable manner.
India is also a party to CBD and therefore, committed to developing an inventory of its biodiversity resources. This documentation of indigenous knowledge with respect to biodiversity is a major task as our biodiversity is also under threat from Intellectual Property Rights issues.
However, for an effective conservation, management and sustainable use of our tree resources, it is imperative that we first develop a sound taxonomic database of the same. In years to come, dendrologists must play an important role in getting the sovereign right of our country on our remaining tree wealth. In addition, when human induced climate change is altering species distribution and extinctions in the forest landscape, the role of a forester- dendrologist has more practical significance in biodiversity conservation.
History of Plant Classification:
The illustrious Greek scientist, Theophrastus (ca.370 – ca.286 B.C.), is considered the first to propose a system of plant classification, which he described in his two works Historia Plantarum and De Causis Plantarum. It is believed that Theophrastus proposed the four plant categories namely trees, shrubs, under shrubs and herbs. Dioscorides in his De Materia Medica (Latin) also listed and described the substances used for medical purposes and their therapeutic properties and uses.
The European naturalists in the 16th, 17th and 18th centuries increasingly began to discuss un-encountered plants and animals from their overseas voyages. So the need to develop a classification system so as to organize these unknown plants and animals became necessary. Herbalists like Otto Brunfels (1464-1534), Leonhard Fuchs (1501-1566), Matthias de L’Obel (1538-1616), John Gerard (1545-1612) and Charles de L’Ecluse (1526-1609) attempted various classification schemes.
Andrea Caesalpino (1519-1603) organized plants by fruits and seeds. In the 17th century, Joseph Pitton de Tournefort (1656-1708) used a form classification that divided plants into groups based on petal characters. He also developed the modern “genus” concept.
His contemporary John Ray (1628-1705) classified some 18,000 species in his Methodus Plantarum (London 1703), using a system based on form and gross morphology of plant structures. In the 18th century, Michel Adanson (1727-1806) grouped plants by affinities observed through multiple relationships of characters which helped to establish the concept of natural classification.
Carolus Linnaeus (1707-1778) decided to try his artificial system, in which he classified plants by counting their stamens and pistils. He created the sexual system consisting of 24 classes based on the number and arrangement of stamens in each flower. Within each class, the plant was then assigned to an order based on the number of pistils in each flower. Linnaeus, through his Species Plantarum (1753) also proposed the concept of binomial nomenclature.
Natural systems, based on morphological relationships emerged during the fag end of 18th century. Antoine Laurent de Jussieu (1748-1836), George Bentham (1800-1884) and Sir Joseph Dalton Hooker (1817-1911) developed natural systems of plant classification by placing together plants having similar combinations of characters. Both De Jussieu and Bentham and Hooker separated the seed plants into three classes namely, dicots, monocots and gymnosperms.
By the middle of the 19th century, new plant classifications emerged based on evolutionary development and phylogenetic concepts put forth by Alfred Wallace and Charles Darwin. Adolf Engler and Karl Prantl’s system, though not truly phylogenetic, is one such system.
The American taxonomist, Charles E Bessey (1845-1915) developed a more convincing phylogenetic plant classification system, by realigning Bentham and Hooker’s natural classification. The plant classification schemes put forth by John Hutchinson, Fuller and Tippo (1954) and Cronquist (1981) are also examples of phylogenetic system.
Bentham and Hooker’s Natural System:
George Bentham (1800-1884) and Sir Joseph Dalton Hooker (1817-1911), the two famous British botanist’s closely examined and placed 97,205 species of seed plants in 202 orders (now referred to as families) based on their morphological relationships. They produced a three volume book called Genera Plantarum.
Their natural system is a refinement of those by de Candolle and by Lindley, which in turn were based directly that of de Jussieu. Most of the plants were classified into either class dicots or monocots, which were subsequently subdivided into sub class, series, orders, family, genus and finally the species.
The refinements made by Bentham and Hooker can be seen in Polypetalae, where the new series Disciflorae are interpolated between the Thalamiflorae and the Calyciflorae. They also revised Monochlamydeae. The gymnosperms were treated as a third taxon collateral with and placed between the dicots and monocots. This system of Bentham and Hooker is being followed in India, United Kingdom and several other Commonwealth countries. It is also used in a number of herbaria and botanical gardens all over the world, including Kew herbarium.
The most important merit of Bentham and Hooker system is that an unknown plant can be easily identified by studying its morphology and by applying a logical process of elimination. For example: Dicots from Monocots and Polypetalae from Apetalae or Gamopetalae.
Further, this is a natural system which is based on actual examination of specimens. It is to be reasonably believed that the authors had some notion about evolutionary trends. For probably that reason, they placed Monocots, which are more advanced than Dicots, in the end of the classification scheme.
At the same time, the placement of Gymnosperms after Dicots which goes against the accepted evolutionary principles is considered as a demerit of this system. The creation of the sub-class Monochlamydae, which is actually a mixed grouping of un-related plants, is also considered as a demerit. The positioning of Orchidaceae, a group of highly advanced plants, as the first family in Monocots also defies evolutionary concepts.
International Code of Botanical Nomenclature:
Use of botanical names and coinage of new botanical names is not to be done arbitrarily but must always follow standard procedures. The International Code of Botanical Nomenclature or ICBN codes have worldwide acceptance which basically outlines provisions for having a stable method of naming taxonomic groups, avoiding and rejecting the use of names which may cause error or ambiguity.
The ICBN codes is intended to sort out errors and ambiguities arising from past misunderstandings and misidentifications and to ensure correct naming of new taxa. The ICBN sets the formal starting date of plant nomenclature at 01 May 1753, the publication of Species Plantarum by Linnaeus (or at later dates for specified groups and ranks).
The first attempt at developing an international agreement was made in Paris in 1867. Here, in the first International Botanical Congress called by the Swiss Botanist Alphonse de Candolle, the first set of International Rules of Botanical nomenclature was adopted along with the “Paris Code”.
Later, in 1892, a group of US botanists held a meeting in Rochester at which they presented some additions and modifications that they considered more objective. They proposed modifications of the Paris Code, but these modifications later presented at the second International Botanical Congress were not accepted.
In 1930, taxonomists finally agreed on a single International Code of Botanical Nomenclature which will be revised every 6 years. The goals of all the revisions will always to achieve stability in scientific nomenclature. The revisions will be published in Taxon, the journal of the International Society of Plant Taxonomists.
There are six principles that guide decisions concerning the code which include uniqueness principle (principle IV), type principle (principle II), priority principle (principle III), retroactivity principle (principle VI) and principles I and V. Proposals will become valid until they are voted on at the subsequent International Botanical Congress.
Identification of Trees in a Tropical Forest Landscape:
In a tropical forest, it is seldom possible to even remotely examine the various vegetative and reproductive characters of a tree species. The tree in question may be quite large and occupying a top canopy. Even with the help of a good binocular it will not be easy to grasp the morphology.
In such a situation, a fallen leaf, flower, fruit or even a seed may be of much value to fix the identity of a tree species. By noticing the nature of the branching pattern, the characteristics of the bole or, if possible, by cutting a blaze, one can also achieve equal success in tree identification.
Presented below are some typical diagnostic features which can be used to pin point a tree species in a tropical forest ecosystem:
1. Leaves:
Leaves can be simple (e.g. Many members of Magnoliaceae, Dipterocarpaceae, Lauraceae etc.) or compound (as in Meliaceae, Fabaceae etc.). Compound leaves may be digitate (Ceiba, Bombax), pinnate (Meliaceae), bipinnate (Albizzia), tripinnate (Moringa) or quadripinnate (Oroxylum indicum). The typical leaf of Bauhinia spp. is bifid. Lobed leaves are typical of Sterculiaceae. Leaves with a conspicuous intra-marginal vein may belong to Myrtaceae (Syzygium spp.).
Leaves with glandular dots are very common in Rutaceae and Myrtaceae. In Zizyphus (Rhamnaceae), Cinnamomum (Lauraceae), Grewia (Tiliaceae), Trema (Ulmaceae) and Strychnos (Loganiaceae), 3-5 basal nerves can be found arising from the base of the leaves. The leaves of many Elaeocarpus spp., Terminalia catappa and Ailatnthus triphysa turn bright-red before falling.
The leaf-surface of many trees may be covered with various types of hairs or glands. The leaves of teak, when rubbed between the hands colour them red. The under-surface of the leaves of Mallotus philippensis has crimson glands. The leaves of many Holigarna spp. are allergic to a few.
2. Branching:
The nature of the branches of certain tree species is also quite distinctive. Trees of the genus Garcinia, Bombax ceiba, Polyalthia fragrans and Terminalia catappa have a characteristic whorled appearance and can be recognized at a glance. Polyalthia longifolia, Cananga odorata and most Pinus spp. have a drooping nature.
3. Bole:
The shape of the bole is also often very helpful in tree identification. The bottle shaped stem of the palm Roystonea regia is a classical example. Both Bombax ceiba and Ceiba pentandra has a round bole and also plank buttresses.
Other tree species with prominent buttressing nature include Tetrameles nudiflora, Palaquium ellipticum and many Ficus and Terminalia spp. Trees like Baccaurea courtallensis, Couroupita guianensis, Saraca indica and many species of Ficus exhibit cauliflory. The bole of Bombax ceiba, Xanthoxylum rhetsa, Zizyphus spp., Flacourtia spp. and Erythrina spp. are covered with spines of various texture. The sheaths of the leaves of the climbing palms, Calamus spp. develop needle-like spines.
4. Bark:
Generally the bark of trees in the evergreen forests will be smooth natured and light coloured with a green tinge. On the other hand, the deciduous tree species display an array of colour and textures. Also, the bark of a young tree is often smooth and of a different colour from that of the old tree. Trees with a smooth bark are many species of Ficus, Tetrameles nudiflora, Garcinia spp., Hevea, Morus and many members of Lauraceae, Myristicaceae and Leguminosae.
Examples of trees with fissured bark are Shorea, Pinus, Calophyllum, Erythrina, Moringa etc. In Aporosa spp. and in Bischofia javanica, the bark is powdery in nature. In some species, the bark exfoliates. Examples include, Gmelina arborea, Terminalia arjuna and Manihot glaziovii. The tree species Lagerstroemia parviflora exfoliates and display its creamy white bark and so the nick name, “naked maiden of the forest”. Using the “crocodile-skin bark”, a Terminalia tomentosa could be quickly identified. The silvery smooth bark of Sterculia urens is a typical sight in a tropical dry deciduous forest.
5. Roots:
Tree roots also have an important diagnostic value. For example, pneumatophores are very common among the various species of the mangrove genera, Avicennia and Sonneratia. Carallia brachiata (Rhizophoraceae) also have aerial rootlets on stem and branches. Stilt roots are common in many Rhizophora spp., Bruguiera sexangula and Elaeocarpus spp. The aerial roots of certain Ficus species, especially the banyan tree is well known.
6. Plant Sap/Latex:
In some trees, when a blaze is taken, the nature of the juice (sap) oozing out is a key diagnostic character. White latex is produced by all the species of Apocynaceae, Asclepiadaceae and some members of Euphorbiaceae. The juice of Anacardiaceae is acrid in nature. Yellow latex is produced by most species of Garcinia. The red latex produced by Bischofia javanica and most species of Myristicaceae is a key spot character.
7. Blaze Colour:
The colour of the blaze also plays a key role in tree identification. The sulphur-yellow coloured blaze of Zanthoxylum rhetsa is quite typical. Red coloured blaze is characteristic of Buchanania lanzan, Boswellia serrata, Bischofia javancia and many members of Myristicaceae. The blaze is creamy white in Alstonia scholaris, Dysoxylum malabaricum and Firmiana colorata. The blaze of most Lauraceae members is aromatic, especially Cinnamomum spp.
8. Fruit:
Familiarity with the fruits of many trees may help us to identify the family, genera or species easily. The “pod” belongs to Leguminosae and comes in various sizes and shapes. Fruits are round in the case of Hydnocarpus and Pterygota alata (Sterculiaceae), while it is spherical in Annona (A. squamosa and A. reticulata), Ficus spp. and Artocarpus hirsutus. Capsules containing seeds enveloped in floss are found in Malvaceae and Bombacaceae. Follicle is the common form of fruit, especially in Apocynaceae, Asclepiadaceae, Bignoniaceae, Moringaceae and Sterculiaceae. Winged fruits can be seen in Dipterocarpaceae. In Coniferae and Bignoniaceae, winged seeds can be found.
Floral Diagram and Floral Formula:
The floral diagram represents the numbers and relationships of the parts of a flower using basically four concentric circles to represent the calyx, corolla, androecium and gynoecium. Using internationally accepted symbols, the position of the stamens, type of placentation etc. will be drawn.
A floral formula is a representation of the structure of a flower using specific letters, numbers and symbols. Typically, a general formula will be used to represent the flower structure of a plant family rather than a particular species.
The following representations are used:
Ca = calyx (sepal whorl; e.g. Ca5 = 5 sepals)
Co = corolla (petal whorl; e.g., Co3(x) = petals some multiple of three)
A = androecium (whorl of stamens; e.g., A∞ = many stamens)
G = gynoecium (carpel or carpels; e.g., G1 = monocarpous)
G = ovary inferior to insertion point of the other whorls. The floral whorls are epigynous to the gynoecium
G = ovary superior to insertion point of other floral whorls. The floral whorls are hypogenous to the gynoecium.
X: to represent a “variable number”
∞: to represent “many”
Collection and Submission of Herbarium Specimens:
What is Herbarium?
A herbarium is a collection of plant specimens that have been pressed, dried and mounted and are arranged in the sequence of an accepted classification and are available for reference or other scientific study. Generations of naturalists have collected plants and mounted them onto sheets of paper, which now serve as historical records. For example, Carl Linnaeus collections numbering approximately 14,300 are still there in the Linnaean Society of London’s herbarium.
In olden days, it was common practice to mount each specimen together with a label on a sheet made from good quality paper. Even before that, botanists pasted or stitched plant specimens on notebooks. These collections were housed in herbariums. In 1545, in the University of Padua, Italy, the first herbarium of the world was established.
Some of the important herbaria of the world include Royal Botanical Garden (Kew, England), British Natural History Museum, Forest Research Institute (Dehradun, India) and the herbariums of the Botanical Survey of India (Lucknow) and its regional centres.
Pressing and Mounting Tree Specimens:
Press each tree specimen as and when it is collected. The specimen will retain its original features if it pressed and dried without loss of time. Tree specimens should be cut and not torn off from the host plant. A sharp knife or sometimes even a sharp razor blade will be enough for making a neat and clean cut.
While selecting plant specimens, go for a true representative. Avoid specimens which are damaged or suffering from disease or pest attack. Avoid sterile specimens and collect only flowering twigs. This is because, reproductive characters, unlike vegetative characters are more constant and could serve as an easily identifiable trait. The size of the specimen should be restricted to the size of the pressing paper (usually 40 cm x 30 cm made from quality handmade paper). Make sure to leave one or more parts (especially leaves) with its lower side uppermost.
After collection, the specimen may be kept in between folded newsprint paper and pressed using a steel or wooden herbarium press and left to dry. Brittle stems may be macerated at the point of fold before pressing. Air dry the specimen to a certain degree of crispiness. Ensure that the original colors of all parts are being retained as far as possible.
Properly pressed and dried specimens may be mounted on good quality (usually of handmade paper) herbarium sheets. By applying glue on the lower side of the specimen, the same can be mounted on the herbarium sheet by applying a firm and uniform pressure. Leave it to air dry. Proper entries may be made on the herbarium labels without fail.
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