(a) Enumerate different kinds of trichomes and explain their taxonomic importance. (b) Discuss the advanced features of…

(a) Trichomes and Their Taxonomic Importance Trichomes are epidermal outgrowths, unicellular or multicellular, that differ from emergences, which include subepidermal tissue.

Kinds: non-glandular trichomes are simple (unbranched, uniseriate, as in cotton seed hairs and Cucurbita), branched (dendritic, as in Verbascum), stellate (Malvaceae, Solanum), peltate scales (Elaeagnaceae, Bromeliaceae), T-shaped or malpighiaceous, two-armed (Malpighiaceae, Artemisia), hooked (Cannabis, Phaseolus) and stinging (Urtica, Tragia). Glandular trichomes have a secretory head: capitate (Solanaceae, Nicotiana) and peltate (Lamiaceae, essential oils), and the tentacles of Drosera.

Taxonomic importance: trichome type, density and distribution are stable and heritable, so they are diagnostic at the family, genus and species level: stellate hairs in Malvaceae and Brassicaceae (Alyssum), T-shaped hairs in Malpighiaceae, glandular peltate hairs in Lamiaceae, stinging hairs in Urticaceae. They help separate species within a genus and identify herbarium and powdered drug material, and hybrids. Trichomes also have ecological roles: defence, water retention and reflecting light.

(b) Advanced Features of Asteraceae and Orchidaceae Asteraceae (Compositae) are the largest dicot family, and their advanced features are:

• A capitulum (head) inflorescence with an involucre of bracts, acting like a single flower, with zygomorphic ray florets and actinomorphic disc florets.
• Syngenesious (synantherous) stamens, an inferior bicarpellary, unilocular ovary with one basal ovule, and a cypsela fruit.
• A pappus (modified calyx) for dispersal, and secondary pollen presentation by the style, ensuring cross-pollination.
• Chemical features such as inulin and sesquiterpene lactones.

Orchidaceae, among the most advanced monocots, show:

• Zygomorphic, resupinate flowers (twisted 180°), with the labellum as a modified landing petal.
• A gynostemium (column), fusion of stamen and style, with pollen grouped in pollinia attached by caudicle and viscidium, so a single visit transfers all pollen.
• An inferior ovary, and thousands of dust-like seeds without endosperm, needing mycorrhizal fungi to germinate.
• Epiphytic habit with velamen roots, and highly specific insect pollination, including deceit as in Ophrys.

Both are insect-pollinated families with specialised flowers.

(c) Importance of Ethnobotany in Human Welfare Ethnobotany (term coined by Harshberger, 1895) is the study of the relationship between people, especially indigenous communities, and plants, covering their use as food, medicine, fibre, dyes and in ritual.

Medicine: tribal and traditional knowledge led to Rauvolfia serpentina (reserpine), Catharanthus roseus (vincristine, vinblastine), Artemisia annua (artemisinin, which won Tu Youyou the 2015 Nobel Prize) and neem and turmeric. The Kani tribe's use of Trichopus zeylanicus (arogyapacha) led to the drug Jeevani, with benefit-sharing.

Food and livelihood: wild edible plants, millets, minor forest produce and fibres give nutrition and income to communities.

Conservation: sacred groves and traditional practices protect biodiversity and landraces.

Safeguards: India's Traditional Knowledge Digital Library (TKDL) and the Biological Diversity Act, 2002 prevent biopiracy and ensure benefit sharing.

Ethnobotany thus guides drug discovery, supports tribal welfare, and preserves culture.

(d) Evolutionary Changes during Domestication of Plants Domestication is the selection by humans of plants that differ from wild ancestors, beginning in the Neolithic, about 10,000 years ago.

Changes (the domestication syndrome): loss of seed shattering (non-brittle rachis in wheat and barley); loss of seed dormancy and uniform germination; larger seeds, fruits or tubers (gigantism); reduced branching and apical dominance (maize from teosinte, via tb1); loss of bitterness and toxins; synchronised flowering and ripening; free-threshing grains; changes in photoperiod response; and polyploidy, as in bread wheat (hexaploid). Harvest index and yield increased.

Advantages: higher and more uniform yield, easier harvest, better taste and nutrition, adaptation to cultivation, and food security.

Disadvantages: genetic bottleneck and erosion of diversity, giving vulnerability to pests and diseases (Irish potato blight, 1845; southern corn leaf blight, 1970); dependence on humans, as crops cannot survive in the wild; loss of natural defences and of wild alleles; and loss of landraces, though wild relatives and genomics help breeding.

(e) Cellular Totipotency in Higher Plants Totipotency is the capacity of a living plant cell, even a differentiated one, to regenerate a complete plant under suitable conditions. Haberlandt (1902) proposed the concept; Steward (1958) demonstrated it by growing carrot root phloem cells into somatic embryos and plants, and Vasil and Hildebrandt (1965) regenerated a plant from a single tobacco cell.

Mechanism: differentiated cells dedifferentiate under the balance of auxin and cytokinin, forming callus (an undifferentiated mass), and then re-differentiate, by organogenesis or somatic embryogenesis, into shoots, roots or embryos, through reprogramming of gene expression. Meristematic and parenchyma cells are most competent; some cells, such as mature sieve tubes lacking nuclei, are not. Plants differ from animals, whose differentiated cells are not generally totipotent.

Applications: micropropagation, somatic embryogenesis and synthetic seeds, protoplast and anther culture, regeneration of transgenic plants, and germplasm conservation.