60 | African yam bean | Sphenostylis stenocarpa | Leguminosae | Tubers
61 | Arrowhead | Sagittaria sagittifolia | Aponogetonaceae | Tuberous rhizomes
62 | Chavar | Hitchenia caulina | Zingiberaceae | Tubers
63 | Chinese water chestnut | Eleocharis dulcis | Cyperaceae | Rhizomes
64 | False yam | Icacina senegalensis | Icacinaceae | Tubers
65 | Hausa potato | Solenostemon rotundifolius | Labiatae | Tubers
66 | Lotus root | Nelumbo nucifera | Nymphaeceae | Rhizome
67 | Queensland arrowroot | Canna indica | Cannaceae | Rhizomes
68 | Shoti | Curcuma zedoario | Zingiberaceae | Rhizomes
69 | Winged bean | Psophocarpus tetragonolobus | Leguminosae | Fibrous roots
70 | Kudzu | Pueraria lobata | Leguminoseae | Tuberous roots
These plants have become a part of human diet in sundry places due to their nutritive components such as carbohydrates, iron, magnesium, calcium, zinc, fiber, essential oils, antioxidants, etc. or medicinal values such as stomachic, digestives, stimulants, expectorants, anti-cancerous, anti-spasmodic, disinfectant, etc. or higher dry matter production and calorie generation. Together, these plants are now rated next to cereals as a global source of carbohydrates (Edison et al. 2006; Tundis et al. 2014; Villordon et al. 2014). Some of these plants have gained immense importance and are widely available such as Zingiber officinale, Raphanus sativus, Daucus carota Subsp. Sativus, Pastinaca sativa, Ipomoea batatas, Solanum tuberosum, Alliums, etc., while others that are gaining importance after remaining hidden for a long time period due to their endemic growth and negligence, include Oxalis tuberosa, Ullucus tuberosus, Tropae-olum tuberosum, Maranta arundinacea, Plectranthus esculentus, Hornstedtia scottiana, etc., which have been used by local inhabitants for the purpose of consumption.
The present scenario of the world focuses on meeting food demands of an ever-increasing and diversified population, reducing wastage and adverse effects on the environment and providing healthy, safe, qualitative and nutritious food for all. In order to achieve these goals, emphasis has been on conservation of this enriched biodiversity, exploration of such novel food and medicinal sources, as well as developing means to enhance production, processing and marketing of their products in a holistic and sustainable approach. The focus has resulted in the establishment of gene banks and germplasm collection centers world-wide, such as Central Tuber Crops Research Institute (Thiruvananthapuram, India), International Potato Center (CIP Peru), International Institute of Tropical Agriculture (IITA, Africa), International Plant Genetic Resources Institute (IPGRI, Italy), etc. An understanding of the fundamental structures, distinguishing parameters for key identification, and development and physiological aspects of these crops from an agricultural and food processing point-of-view is thus of immense importance.
2.2 Taxonomy of Roots and Tuber Crops
In 1813, de Candolle gave us the term taxonomy for law of arrangements (taxis-arrangement or order; nomos-law), a science for biological classification. Plant taxonomy is a branch of science associated with plant identification, description, naming and classification on the basis of their specific distinguishable characteristics and features. This study of plants helps in understanding evolutionary patterns and conserves biodiversity with localization of high species richness. The process of identification of plants deals with revealing an unknown plant’s identity by comparing it with other known plants based on specific features described in monographs, manuals, revisions, etc., herbariums or other live samples. Study of shape or form of a plant or its parts, such as morphology, also aids in identification of plants and their proper description, naming and arrangement in groups or taxas based on distinctiveness and similarities.
Many modern techniques studying biochemical patterns, molecular markers, cytogenetic, etc. have enhanced the reliability in identifying an unknown sample with less time and effort. Presently, most of these nearly 50 known roots and tuber crops belong to the Asteraceace (Jerusalem artichoke, Salsify, Chicory, Arctium, Yam Daisy, Black Salsify, Yacon, Dandelion) and the Apiaceae (Arracacha, Carrot, Parsnip, Celery/celeriac, Parsley, Earthnut/pignut, Black cumin, Skirret) family followed by Fabaceae (Yam Bean, Jicama, Ahipa, Bush potato, Breadroot, Hog potato, Earthnut pea). The Araceae family mainly comprises different Taro plants and Yautia crop, while different forms and species of artichoke and Plecranthus belong to the Lamiaceae family only. Maximum variation is observed in crops belonging to the Caryophyllales order. Potatoes, Sweet potatoes and Desert yam are placed in a different family of the Solanales order. Similarly, Arrowroot and Ginger belong to the Zingiberales order with a different family, and Daylilies and bulbous crops such as Onion, Garlic to Asparagales while Mashua, Radish, Turnip, Daikon, Rutabaga and Maca represent the Brassicales order. Besides these, in some families, single edible root and tuber plants have been identified, such as Dioscoreaceae has yams, Cyperaceae has Chufa, Arecaceae has Sago palm, Oxalidaceae has Oca and Malvaceae has Bush carrot.
2.2.1 Morphological Identification
Study of stem, leaves, roots and reproductive parts, their structure, shape, size, position and arrangement providing the overall appearance of a plant, is of utmost importance in its identification.
Leaves Convenience in visualizing the organ has attributed to an ease in morphological studies. Arrangement of leaves in Potatoes and Sweet potatoes is pinnate or palmate, while most of the root and tuber plants belonging to Apiaceae possess long sheathed petioles possessing leaves mostly of a pinnate and lobed nature. However, Black cumin belonging to the same family consists of a finely dissected filliform pinnate leaf. Linear or Lanceolate leaves, or alternate-opposite leave arrangement, mark the plants of the Asteraceae family. Giant swamp taro and Colocasia show the presence of sagittate leaf patterns, while Xanthosoma and Alocasia are demarcated with a margin attached and long elongated petioles respectively. Simple varied-shape leaves, sometimes mucillagenous as in the Mignonette vine, occur in the Caryophyllales order. Short sheaths with varied sized and flattened base leaves are found in Allium cepa. Lanceolate leaves are found in Arrowroot, while the ginger plant belonging to the same order possesses two ranked sheathed base leaves. A crown of large pinnate leaves with highly variable petiole size is found in the Sago palm, while Oca is demarcated by trifoliate leaves. Slender lobed palm-shaped leaves are prominent in the Cassava plant, while Chufa exhibits grass-like leaves accompanied with leaf-like bract involucres. The Plecranthus species specifically has elliptical, oval or oblong reticulate-shaped leaves. The details of the leaf and stem morphology of different root and tuber crops are described in Table 2.2.
Inflorescence and Flower The flower is an organ responsible for seed and pollen grain formation through sexual reproduction in plants. Its conservative nature along with the least environmental susceptibility has favored the study of this organ in identification and class determination of a plant. The root and tuber plants of Solanales are herbaceous and semi-erect with a perennial and mostly trailing vine nature with homostylous or sympetalous flowers. Burdock, Chicory and Salsify belonging to Asteraceae family possess capitula-type inflorescence, while Jerusalem artichoke and Yam daisy belonging to same family has numerous yellow flower heads and scapes along with achnes respectively. Simple or mainly compound umbels are found in Carrot, Arracacha, Parsnip and Celery. Yam bean consists of variable pods and olive-colored seeds. The Plectranthus species is mainly accompanied with bright yellow flowers on short crowded branches. Raceme, corymbiform raceme and silique type of inflorescence are found in plants belonging to the Brassicaceae family, while in Mashua belonging to same order but different family (i.e. Tropaeolaceae) possesses solitary and zygomorph flowers. Similarly, root and tuber crops belonging to the Asteraceae family usually have clustered inflorescence such as spathe, spadix or peduncle, while those of the Caryophyllales order have large, less branched or axillary-type inflorescence. Daylily, Onion and Garlic or Oca mainly have spathe inflorescence or hermaphrodite flowers respectively, Yams and Chufa possess a compound and umbellate type of inflorescence, Sago with a terminal inflorescence state, while cyathia is found in Cassava. The details are shown in Table 2.2.