South Indian B. nothum possessing calyx teeth (well-developed) has been placed in a new section named Austrobunium, separating it from B. kandaharicum, Afghanian species by the help of nrlTS sequence data (Zakharova et al., 2014). Similarly, monophyletic genus Arctium has been broadly redefined based on ITS and cp DNA regions study on 37 species. The morphological evidences distinguishing Arctium from Causinia were also studied by further corroborating molecular data (Vinyal-longa et al., 2011). Phylogeny status of Mannihot genus due to its ambiguousness, was investigated using geneG3pdh located in the nucleus and chloroplast genes. A well-defined clade could be proposed for the Mesoamerican species, while sundry clades were formed for South American species. The estimated age of the Manihot crown was 6.6 million years and the least variations observed from data showed recent diversification in the genus (Chacon et al., 2008). Klaas and Friesen (2002) has reviewed various molecular markers like AFLP, RFLP, etc. used for studying Alliums and concluded that grouping in the phylogeny can be well resolved with the help of chloroplast and nuclear markers, though both techniques possess some gaps and exhibit variations in results, due to recombination occurring in nuclear DNA which cpDNA lacks. Large-scale genus level investigations in Alliums, presently mostly undertake ITS nuclear marker based studies. In another study, 37 alleles were identified across 120 garlic accessions based on 7 simple sequence repeats (SSRs) and average genetic diversity of about 0.586 was obtained based on which phylogram with 4 clusters was developed. The study also emphasized the role of various geographical conditions in making a local selection pressure and adaptability variations on different garlic accessions (Jo et al., 2012). The detailed status of all the root and tuber crops showing their classification level as presented in Table 2.3.
Table 2.3 Taxonomic position of Roots and Tuber crops
Plant Solanum tuberosum
Taxonomic position
― Earlier classification Past taxonomic treatments of wild and cultivated potato have differed tremendously among authors with regard to both the number of species recognized and the hypotheses of their interrelationships. Linnaeus recognized cultivated potatoes, known to him from both Europe and Peru, as a single species, S. tuberosum. De Candolle was the first to name as distinct from the Chilean populations of S. tuberosum, as var. chiloense A. DC.
― Present classification Recent classifications, however, recognize only ~100 wild species and 4 cultivated species.
― Close alliance plants/Origin taxa Arose from wild species in the Solanum brevicaule bitter complex.
Infraspecific classification Hawkes divided the cultivated potato into 7 species and 7 subspecies. Ochoa recognized 9 species and 141 infraspecific taxa for the Bolivian cultivated potatoes alone. Dodds recognized 3 species, S. curtilobum, S. juzepczukii and S. tuberosum, with 5 groups recognized in S. tuberosum, largely defined by ploidy.
Groups Section Petota contains 494 epithets corresponding to wild taxa (including nomina nuda and illegitimate names) and 626 epithets corresponding to taxa that have arisen in cultivation.
Status The taxonomy of section Petota is complicated by introgression, interspecific hybridization, auto- and allopolyploidy, sexual compatibility among many species, a mixture of sexual and asexual reproduction, possible recent species’ divergence, phenotypic plasticity and consequent great morphological similarity among species.
References Ovchinnikova et al., 2011 (continued overleaf)
Plant Ipomoea batatas
Taxonomic position
― Earlier classification
― Present classification Convolvulaceae
― Close alliance plants/Origin taxa Among the species within the genus Ipomoea series Batatas, 13 are considered to be closely related to the sweet potato, but the wild ancestor of this plant is still not identified. The sweet potato was thought to originate from diploid I. leucantha Jacq., from which derived tetraploid I. littoralis Blume by polyploidization.
Infraspecific classification Ipomoea trifida was considered the closest relative of I. batatas, and might be its progenitor. Ipomoea tabascana, which has so far been reported as closely allied with I. trifida and I. batatas, would be interspecific hybrid rather than progenitor of the two species.
Groups
Status Reports on cytogenetics of the genus Ipomoea and especially I. batatas complex are very scarce. The use of molecular cytogenetic techniques may contribute to resolve the relationships between the closely-related species in this Ipomoea series.
References Srisuwan et al., 2006
Plant Manihot esculenta, syn. M. utilissima
Taxonomic position
― Earlier classification Bertram’s phylogenetic analysis was the first using molecular markers to infer the relationships among Manihot species.
― Present classification Schaal conducted a more recent phylogenetic analysis of the genus Manihot based on DNA sequences of the Internal Transcribed Spacer (ITS) of nuclear ribosomal DNA. The cladogram split the species into 2 main clades: one from Mesoamerica and the other from South America. In this phylogeny, M. esculenta is part of the second clade and is closely related to some species of sections Quinquelobae Pax emend. Rogers & Appan and Glaziovianae Pax emend.
― Close alliance plants/Origin taxa Domesticated from a single wild progenitor, M. esculenta subsp. flabellifolia, Cnidoscolus Pohl is its sister genus.
Infraspecific classification Compilospecies with several different wild relatives contributing to its genetic make-up. The clade composed by Manihot alutacea, M. cecropiaefolia, M. longipetiolata, M. orbicularis, and M. sparsifolia is a well- supported relationship, common to all the phylogenies obtained. All these species are found in the Cerrado ecosystem of Brazil (Goiás) and have a shrubby habit. They belong to the Quinquelobae section (except for M. longipetiolata and M. orbicularis), where species such as M. jacobinensis and M. violacea are also included. Another clade common to all the phylogenies was formed by M. glaziovii, M. carthaginensis, M. epruinosa and M. guaranitica. All the species form a part of different taxonomic sections, except for M. glaziovii and M. epruinosa, which belong to the Glaziovianae section, characterized by the presence of trees and tall shrubs.