Proc. Indian Acad. Sci. (Plant Sci.), Vol. 93, No. 2, June 1984, pp. 165-177 Printed in India. Taxonomy of Bidens section Psilocarpaea (Asteraceae-Heliantheae- Coreopsidinae) in India K M M DAKSHINI and PRITHIPALSINGH Department of Botany, University of Delhi, Delhi 110007, India MS rr16216213 Dr162 1983; revised 7 February 1984 Abstract. Critiealexamination ofnumerous spr showed that Bidens sect. Psiloearpaea is represented in India only by B. pilosa var. ~ minor (BI.) Sherffand B. bipinnata Linn. The occurrenceofB. biternata (Lour.) Merr. & Sherffas suggestedearlier could not be established during the presr taxonomic investigation on the genus Bidens in India. Keywords. Bidens; taxonomy; Psilocarpaea. 1. Introduction Delimitation of taxonomic categories is primarily based on the correct appreciation of discontinuities in character va¡ and/or in patterns of geographical distribution. In stable taxa these requisites are generally fulfilled and the taxonomic units are easily de¡ On the other hand taxonomic groups in which phenotypic variability and limited gene exchange exist pose a serious difliculty to the taxonomists. The genus Bidens Linn. belongs to this category (Gillett 1975; Gillett and Lim 1970; Mensch and Gillett 1972; Grierson 1972; Sherff 1937; Weedon et al 1974; Wild 1967). Although only three species of Bidens section Psilocarpaea (characterised by long slender cypselae narrowed from the middle to the top) namely B. pilosa L., B. bipinnata L., and B. biternata (Lour.) Merr. & Sherff have been reported to occur in India, their taxonomic treatments have varied from time to time, and the understanding of their circumscription is still disputed. According to some authors (Chavan and Oza 1961, 1966; Maheshwa¡ 1963; Oomachan and Billore 1969; Rao and Joseph 1965; Rau 1968; Santapau 1953; Saldanha and Nicolson 1976), Bidens biternata (Lour.) Merr. & Sherff is the most common representative of this group, the Linnean B. pilosa is either absent or very rare and B. bipinnata L. is infrequent in its distribution. However, Babu (1977) reported that B. pilosa L. and B. bipinnata L. are frequently dist¡ in the Northwest Himalaya, and remarked that B. biternata "may occur within this area as a weed'. A similar observation on the distribution of B. pilosa L. in S. India was made by Matthew (1981). A comparative analysis of the taxonomic treatments in these floristic accounts clearly demonstrates that the problems related to the identification of these taxa have been largely due to the use of leaf morphology as the main taxonomic character (Babu 1977; Chavan and Oza 1961). In a taxonomic investigation such characters do not generaUy help in identification of a large number of specimens and the discontinuities are not appreciated. Further, the taxonomic distinctness of these three species has been influenced by the views on the synonyms assigned to each taxon. The following brief resum› of the 165 166 K M M Dakshini and Prithipalsingh available literature illustrates the various views on the circumscription and delimi- tation of taxa within the section Psilocarpaea. Clarke (1876) listed Bidens pilosa L. and B. decomposita DC. in his 'Compositae Indicae'. Hooker (1882) segregated B. pilosa L. into three varieties, B. pilosa var. 1 pilosa proper, var. 2 bipinnata, and var. 3 decomposita. Additionally, in his notes Hooker (1882) listed Bidens wallichi DC. as a synonym of B. pilosa var. 2 bipinnata. Duthie (1903) recognised only B. pilosc L. and listed B. bipinnata (i.e.B. pilosa var. 2 bipinnata sensu Hooker) as its synonym. Cooke (1906) considered Hooker's var. 2 bipinnata as 'scarcely worth distinction' in the Bombay Presidency, and thus recognised only B. pilosa L. as the common Indian member of the genus Bidens. Collett (1921), on the other hand, recognised B. pilosa L. and B. wallichi DC. as distinct species, thus not following Hooker (1882) who considered the latter as a synonym of B. pilosa var. 2 bipinnata. Sherff (1937) in his monograph on the genus Bidens pointed out the erroneous treatment by Hooker (1882) of B. bipinnata asa variety of B. pilosa and instead established B. bipinnata L. asa distinct species with the following names as its synonyms: B. pilosa var. 2 bipinnata (L.) Hook.; B. pilosa var. 3 decomposita (Wall. ex DC.) Hook.; and B. decomposita Wall. ex DC. Sherff (1937) also removed B. wallichi DC. from the synonymy of B. pilosa var. 2 bipinnata of Hooker, and considered it as conspecific to Bidens biternata (Lour.) Merr. & Sherff. Further, in his notes under B. bipinnata (Sherff 1937 p. 372) and B. biternata (Sherff 1937 p. 399) he commented that due to the superficially intermediate leaves, 'B. biternata (= B. wallichi DC.), a species very common in British East India', was erroneously equated by Hooker with B. bipinnata. Santapau (1953) overlooked 'British East India' in the above statement of Sherff (1937) and remarked: 'This (i.e. Bidens biternata) is the plant known to the w¡ of the Indian Floras as B. pilosa. Sherff in his recent monograph on the genus Bidens has shown that the common Indian plant is not the Linnean plant. Subsequently ali the floristic accounts published by Indian taxonomists dealt with B. biternata (Lour.) Merr. & Sherff as the common Indian Bidens with B. pilosa auct. non Linn. as its synonym (Chavan and Oza 1961, 1966; Maheshwari 1963; Oomachan and Billore 1969; Rao and Joseph 1965; Rau 1968; Saldanha and Nicolson 1976). In recent years some taxonomists who regard the common Indian plantas Bidens biternata (Lour.) Merr. & Sherff also reported the occurrence of the Linnean B. pilosa as a rare plant from several parts of the country (Chavan and Oza 1961, 1966; Oomachan and Billore 1969; Panigrahi et al 1964; Saldanha and Nicolson 1976; Santapau 1961). Bidens bipinnata L. has also been reported asa new record from different parts of the country (Babu 1977; Chavan and Oza 1966; Dakshini and Prithipalsingh 1971; Raizada 1976; Saldanha and Nicolson 1976). Thus the taxonomy and nomenclature of B. pilosa, B. bipinnata, and B. biternata in our country are in a confusing state. There is an important need to clear this confusion especially because these taxa forma weedy community. The present paper deals with the taxonomy and nomenclature of Bidens section Psilocarpaea in India. 2. Materials and methods Following the suggestion that 'species and lower taxa should be formulated around natural populations' (Davis and Heywood 1967), plants were sampled from natural populations ofBidens taxa from different regions of India. These plants were examined Taxonomy of Bidens 167 to establish the extent of variation in vegetative (particularly leaf morphology) and floral (capitulum morphology, organisation, phyllaries, cypselae, etc) characters. These studies were supplemented with a critical examination of herbarium specimens available in the major Indian herbaria, and also ofphotographs ofauthentic specimens located at Kew, Gray, Field Museum of Natural History, and British Museum (Natural History) herbaria. We have followed Sherff (1937) for typification of relevent taxa and location of type specimens. 3. Resuits and discussion The specimens examined fall in two distinct groups. The characters studied in detail and the range of variation in these characters are summarised in table 1. Leaf morphology is highly variable (Figures 1-6). Even within these two groups different patterns could be identified based on the degree of dissection of the lamina and the shape of ultimate segments. It is amply clear from these data that such va¡ vegetative characters overlook discontinuities in more stable reproductive characters. It is prima¡ due to the reliance on leaf morphology that there has been an erroneous identification of the Bidens taxa by earlier workers. However, our observations show that it is easy to establish the range of distinct discontinuities in the characters of flowering and fruiting capitula and more particularly on the cypselar morphology, and thus highlight the use of these characters for the delimitation of Bidens species. A similar suggestion for delimiting the species ofsection Psilocarpaea was made by Sherff (1937) who emphasised the importance of the morphology of involucral bracts, number of total and ligulate florets per capitulum, cypselae morphology, and number of awns per cypsela. Unfortunately these suggestions did not influence a majority of Indian taxonomists. Similar to Sherff's (1937) observations, we have also found that the monomorphic cypselae is a very important feature for distinguishing Bidenspilosa L. from B. bipinnata L. and B. biternata (Lour.) Merr. & Sherff. The iatter two species have dimorphic cypselae within a single capitulum. Of these, B. biternata has glabrous outer cypselae and hispid (but not tuberculate-hispid) inner ones, while in B. bipinnata the outer cypselae are tuberculate-hispid and the inner ones are sparsely hairy in the upper-half and glabrous in the lower-half. In the Indian B. pilosa L. all the cypselae in a capitulum are linear-curved, black, and tuberculate-hispid either apically or thorough- out their length. Similarly, in B. bipinnata Las represented in India, the dimorphic cypselae within a single capitulum are all linear, but differ in their size, colour and surface patterns. The outer cypselae which are tuberculate-hispid are generally brown in colour, but sometimes they may be hispid only and then blackish-brown. The inner ones are black and generally glabrous throughout their length or occasionally very sparsely hairy only in the apical region. Recognising that variation in cypselar morphology is an important character for identification, and on the basis ofa correlative assessment ofcharacters listed in table 1 and taking the data presented by Sherff(table 2) into account, the two groups ofplants commonly occurring in India conform to (i) B. pilosa var. fl rainor (BI.) Sherff (group I plants in table 1) and (ii) B. bipinnata L. (group II plants in table 1). Contrary to earlier observations, none of the material now examined could be assigned to B. biternata (Lour.) Merr & Sherff as defined by Sherff (1937).