― Stem Perennial twining herbs or shrubs
― Leaf Leaves are trifoliate with entire or slightly 3-lobed leaflets, pubescent, 5–12 cm long and 4–10 cm breadth.
― Flower/Fruits Flowers are borne in dense, pubescent racemes 20–50 cm long, are mauve to violet and fragrant. The pods are flat, oblong-linear, 5–10 cm long, hairy with 8–20 seeds.
Genetic Makeup
References www.nzdl.org site with book title “Root crops” authored by Kay, D.E. (1987)
Root Morphology Taxonomical description of a plant based on root morphology poses constraints such as inaccessibility of the organ due to its underground behavior, less distinctive features and lack of appropriate methods. Presence or absence of spatial scores, quantitative analysis of species’ root distribution in conjugation with root densities and spread and allocation of roots to respective plant or taxa, aids in proper taxonomical study of plant on its root basis. However, the study termed “Root Research” is in its infancy. General morphological root traits, also known as gross morphology, are used for taxa identification. Concerned criteria includes study of root color, odor, resilence nature apropos to breakage, nature of inhabitant myc-orrhiza, root hairs or resins and its abundance, woody structure, study of exodermal structure or peridermis characters, root branches and its pattern, root tip density, root diameter, morphotype of mycorrhizal root tips, texture, tensile strength and overall biomass distribution.
Root staining helps in better identification of a roots’ morphological and color differences (Rewald et al., 2012). Moreover, near-infrared reflectance spectroscopy is an easy, fast and low-cost intensive technique used for root biomass determination. In-situ observations on species-specific root distribution, growth and interactions are easily detected through minirhizotron pictures of fluorescent roots. In addition, intra-specific root indentification is done by incorporation of radioisotopes, mainly C13, which differentiates C3 and C4 plants based on their root tissues (Rewald et al., 2012). Though these parameters are subjected to environmental and geological changes and require excessive labor, skill and time, the low-cost intensive nature along with ease of propagation under in-situ conditions maintain the utility and applicability of roots for taxa identification.
Tubers of Amorphophallus species vary in shape, some being uniformly globose, while in others they may be clustered or elongated (Figures 2.41 and 2.42). Allium cepa (Figure 2.44) has bulbs with reduced discs with globose type scapes, 1.8 m tall tapering to base, vari-colored membranous skin contrary to Allium sativum (Figure 2.43), and side-elongated densely packed clove bulbs in a single layer arrangement. Stachys affinis (Chinese artichoke) tubers are shorter, thicker, branched surface rhizomes, segmented oblong (Figure 2.39), while its family relative, the Plectranthus species, possesses stolon-type yellow-brown pigmented tubers. Yacon is a sweet tasting, crisp tuber. Most plants of Asteraceae (Figures 2.34-2.39), classified under root and tuber crop groups, possess mainly a tap root. However, Jerusalem artichoke of the same group is marked by its fibrous nature, ginger root-shaped, with brown- to red-colored roots (Figure 2.33). Turnip has a stout fusiform tuberous root with various colors and shapes of swollen hypocotyls (Figure 2.29). Maca has a fleshy turnip-shaped, tap root with variable color hypocotyls (Figure 2.32), while radish belonging to the same family has long, tapered fleshy roots (Figure 2.30). To the contrary, the Mashua tuber (Figure 2.28), belonging to the same order as of Maca, Turnip and Radish, has black, white and purple-grey tubers with deep, narrow-eyed structures. Pachyrhizus species of the Fabaceae family have fleshy tuberous roots with succulent white interiors (Figure 2.25). Thick rhizomes and tubers are found at stem base and leaf axils in the Mignonette vine belonging to the Basellaceae family of Caryophyllales, while Ulluco of the same family which has a widely colored, twisted, round, cylindrically elongated tuber with superficial eyes (Figure 2.22).
Beets belonging to the Amaranthaceae family of the same order are characterized by their stout, swollen roots with hypocotyls (Figure 2.23). Oca is identified by its gamut color variations in tuber skin and bract covered eyes. The tubers are cylindrical, claviform and ovoid in shape (Figure 2.21). Black-brown, hard to smooth globose tubers are characteristic of Chufa (Figure 2.20). Ginger belonging to the Zingiberales order has a buff-colored surface, and is a horn-shaped rhizomatous spice (Figure 2.19), while bract-enclosed, subterranean, long pointed tubers belong to the same order as Arrowroot (Figure 2.18). Root and tuber crops of the Apiaceae family mainly possess a conical-cylindrical taproot (Figures 2.12-2.17). Yams are mainly characterized by their six short underground tubers (Figures 2.9–2.10), while corms mainly arise in the Araceae family (Figures 2.6–2.8). Cassava roots are usually accompanied by fibrous bark and yellow-white-colored flesh (Figure 2.5). Sweet potato is a long, tapered, multi-colored fleshed tuberous root (Figure 2.4), while Potato is an astolon-shaped root with a vari-colored skin covering depending on the cultivars (Figure 2.3).
The detailed root and tuber morphology of plants are illustrated in Table 2.2. In addition, the variations in root morphological characters of sundry root and tuber crops, giving them distinct appearance and identification scores, are shown in Figure 2.
2.2.2 Cytogenetics
Intra-specific changes in genomic size have been related to species divergence and evolution, thereby acting as a useful taxonomic marker (Ohri, 1998). Classical kary-otypic studies reveal alterations in chromosome number and morphology and disclose diversity, which remains unapparent in morphological studies. Different parameters supporting the study include counting of chromosome numbers, frequencies of different haploid numbers in various species and fluorescent in-situ hybridization (FISH) marking chromosomes along with Bayesian analysis.
Fruit and seed production, pollen grain size, vegetative morphology, ploidy level and exine sculpture are some of the valuable features which were studied by Xifreda et al. (2000) to cytotaxonomically differentiate two A. cardifolia infraspecific genus, namely subsp. gracillis and subsp. cardifolia. Similarly, somatic chromosome number, interphase chromosome value and heterochromatin value were analysed during karyotype studies of seven C. esculenta varieties localized in Bangladesh (Parvin et al., 2008). The close relationship between Calathea and Maranta belonging to the same family Marantaceae has been well corroborated by cytological studies (Sharma and Bhattaracharya, 1958). Nowadays, various anti-mitotic agents and inhibitors such as oryzalin, trifluralin and amiprofos-methyl (APM) have been used for the cytogenetic compression and elongation of chromosomes with accurate morphometric analysis for metaphase studies. Physical mapping, chromosome identification and evolutionary analysis, especially in species with large genomes, is done through cDNA libraries and repetitive sequences like microsatellites, etc. occurring in abundance in plant genomes transforming into extremely valuable FISH markers (Chester et al. 2010; Soltis et al., 2013). Srisuwan et al. (2006) studied hexaploid Ipomoea batatas (10 varieties), tetraploid Ipomeoa trifida (5 accessions) and six other related species by FISH apropos to organization and distribution of 5S and 18S rDNA and asserted that the higher ploidy level is often marked by decrement in the 18S rDNA loci. Data generated showed greater closeness between I. trifida and I. batatas, as well as between I. tiliacea and I. leucantha.