Vigna yadavii (Leguminosae: Papilionoideae), a new species from Western Ghats, India

Abstract A new species of Vigna Savi, subgenus Ceratotropis (Piper) Verdc., Vigna yadavii S.P. Gaikwad, R.D. Gore, S.D. Randive & K.U. Garad, sp. nov. is described and illustrated here. It is morphologically close to Vigna dalzelliana (Kuntze) Verdc. but differs in its underground obligate cleistogamous flowers on positively geotropic branches, hairy calyx, small corolla, linear style beak and dimorphic seeds with shiny seed coat.


Introduction
Vigna Savi is a large pantropical genus of the tribe Phaseoleae with 90 species distributed in six subgenera (Thulin et al. 2004, Delgado-Salinas et al. 2011, Tomooka et al. 2010). Among the subgenera of the genus Vigna only the subgenus Ceratotropis (Piper) Verdc. has its center of species diversity in Asia and it is popularly known as Asian Vigna (Tomooka et al. 2002b (Tomooka et al. 2002a, Tomooka et al. 2010). However, Aitawade et al. (2012) have described a new species V. sahyadriana Aitawade, K.V. Bhat & S.R. Yadav from India recently. Thus, the number of species in the genus Vigna subgenus Ceratotropis is now 23.
During field survey of plants of the family Leguminosae -Papilionoideae in Western Ghats of India, the authors collected an interesting species of Vigna on hill slopes at about 1200 m elevation above mean sea level in Nasik and Satara districts of Maharashtra, India. It interestingly possesses underground cleistogamous flowers on positively geotropic branches. This unusual character of Vigna species encouraged its detailed study, which revealed that it represents an un-described species of the genus Vigna subgenus Ceratotropis. It has been confirmed by the perusal of relevant literature (Maréchal et al. 1978, Tateishi 1984, Babu et al. 1987, Tomooka et al. 2002a, Tomooka et al. 2002b, Tomooka et al. 2010, Maxted et al. 2004, Thulin et al. 2004, Lewis et al. 2005, Delgado-Salinas et al. 2011, Aitawade et al. 2012and Aitawade et al. 2012) and experts' opinion on the identity of the species. It is described and illustrated here.
Flowering and fruiting: August-November.

Diagnosis
Vigna yadavii is morphologically close to Vigna dalzelliana (Kuntze) Verdc. but differs in its underground obligate cleistogamous flowers on positively geotropic branches, hairy calyx, small corolla, linear style beak and dimorphic seeds.

Etymology
The species is named in honor of Prof. S.R. Yadav, Department of Botany, Shivaji University Kolhapur, India (MS), in recognition of his valuable contribution to taxonomy of flowering plants of Western Ghats of India.

Notes
Vigna yadavii shows morphological similarities with Vigna dalzelliana (Kuntze) Verdc. but differs from the latter species by the characters given in Table 1. The presence of underground obligate cleistogamous flowers on positively geotropic branches is most useful distinguishing characteristics of V. yadavii. In addition to this, dimorphic seeds and differences in hilum, aril, style beak and corolla are also useful distinguishing characteristics of the new species. Vigna dalzelliana has a unique flattened style beak but that of V. yadavii is linear. The poorly developed aril of seeds of the cleistogamous flowers is also diagnostic feature of V. yadavii.
absent Seeds 3-5 per pod, whitish brown, 2-3 × 1.7-2 mm; hilum poorly developed and not protruded out. absent During rainy season (August-November), the species produces chasmogamous flowers on aerial branches and underground obligate cleistogamous flowers on positively geotropic branches. The cleistogamous flowers are much smaller than chasmogamous flowers and white-albino in color. They remain closed. The pods of cleistogamous flowers are colorless, short, curved and 3-5-seeded. There are no structural differences in chasmogamic and cleistogamic flowers except for the smaller size and white albino color of the latter.
India, Kolkata and Dr. I.S. Bist, Principal Scientist, National Bureau of Plant Genetic Resources, New Delhi, India for their expert comments on identity of the species, and to J.F. Veldkamp, National herbarium of the Netherlands (NHN) for Latin diagnosis and verification of gender ending of new species.