Leguminosae Is One of the Three Largest Families of Flowering Plants

I. INTRODUCTION Leguminosae is one of the three largest families of flowering plants. It includes varying numbers of genera and species ranging from 550-690 genera and 12,000-17,000 species (Airy Shaw, 1966; Hutchinson, 1964 and Melchior, 1964). It is well represented in tropical and sub-tropical countries, being most numerous in tropical America. The great number of genera of Caesalpiniaceae occur in tropical Africa and tropical America. In tropical Africa about fifty six and in tropical America about forty are being endemic (Hutchinson, I964). As many as two hundred species of Cassia L. alone are represented in the flora of Brazil (Rendle, 1925). Only about eight genera occur in both tropical Africa and America. In Malaya, New Guinea and tropical Asia there are about eleven genera. In Madagaskar there are nine endemic genera. It is poorly represented in Polynesia, South China, Australia and extra tropical region of South America; while in north temperate zone only about three genera occur. A few genera have a distribution of special interest, viz., Dalhousie_a d. Grah. in India and Western tropical Africa; Bowringia Champ, ex Benth. in East Asia and Vi/estern tropical Africa; Calpurnia E. Mey. in South India and Africa, Gladrastis Rafin in North East and Eastern Asia. Miraosaceae is mainly of Southern Hemi sphere. Most of the African genera seem to be more modern development of the group, the headquarters of which is in South America. In the Papilionaceae, Wiich is world wide in distribution; the more primitive woody genera are confined to the Southern Hemisphere and to the tropics, the more advanced and herbaceous genera to temperate regions and numerous Mediterranean countries. The tropical rain forests are rich in species of Caesalpiniaceae and Mimosaceae along with arborescent forms of the Papilionaceae (Tribe - Dalbergieae). In deciduous forests where the growth is interrupted by cold vdnter, leguminous trees are rare; herbaceous Papilionaceous members become more important features of vegetation in such regions. Papilionaceous members play important role in Steppe formations. The family is well circumscribed, showing significant evolutionary tendencies in the leaf type, carpel morphology and number, zygomorphy and reduction of floral parts. However, opinions have sharply differed as regards the status and posit ion of it and the inclusion of the three sub-families, Gaesalpinoideae, Mimosoideae, Lotoideae (Papilionoidaae, Faboideae, Papilionatae ) and the fourth sub-family Swartzioideae, in it. They are recognised some times as separate families - Caesalpiniaceae, Mimosaceae, Fabaceae (Papilionaceae) and Swartziaceae. Bentham and Hooker (1^55) treated Leguminosae as an Order in their "Genera Plantarum", dividing Order into sub-orders - Papilionaceae, Caesalpiniaceae and Mimosaceae. jummosae divided into the and Mimosaceae. In the classification of Taubert (1894) given in Engler and Prantl's (1894) "Die Naturlichen Pflanzen Familien", Leguminosae is divided into three sub-families, viz., Mimosoideae, Caesalpinoideae and Papilionatae. Taubert (1894) considered Mimosoideae first under Legumi nosae; while same group of plants was treated as the third by Benthara and Hooker (1865) and Baker (187&). But there was no dispute about the position of Caesalpinoideae as it was ranked as second by them. Bessey (1915) included number of families in the Order )sales. He treated Mimosaceae in the Order ^sales. He treated Mimosaceae, Gassiaceae and Fabaceae as the families of the Order Resales, but substituted the terms Gassiaceae for Caesalpiniaceae and fabaceae for Papilionaceae. Hutchinson (1926) considered Leguminosae as an Order and remarked "a prolific and highly successful group derived from the Resales though the Mimosaceae, Caesalpiniaceae and Papilionaceae as the families of the Order Leguminales." But in 1964, he (Hutchinson, 1964) modified his previous views regarding the origin of Leguminosae and suggested that the Caesalpiniaceae was the most primitive family in this Order and was clearly related to the liosaceae. He connected the genus Bauhinia L. of Gaesalpiniaceae, to the tribe Chrysobalaneae; which is the most advanced tribe of Rosaceae. In the tribe Chrysobalaneae, the flowers are zygomorphic and fruits resemble legumes. Hutchinson (1954) considered Papilionaceae as the most advanced family of the Order Leguminales. Schnarf (1931) included Mimosaceae and Papilionaceae as fam.ilies under Order Resales, but considered Caesalpi- noideae and Papilionatae as two sub-families of Papilionaceae. Warming (1932) recognised these as three families and treated them in one sequence Gaesalpiniaceae, Papilionaceae and Mimosaceae. Wettstein (1933~193 5) recognised Mimosaceae and Leguminosae as the families but treated Gaesalpinoideae and Papilionatae as sub-families of Leguminosae. Wodehouse (193 5) followed Wettstein. Bailey (1949) considered Leguminosae as family that included the sub-families - Lotoideae, Gaesalpinoideae and Mimosoideae. Gundersen (1950) followed Wettstein in treating Gaesalpinoideae and the Papilionatae as the sub-families of Leguminosae, but treating Mimosaceae as a family at par with Leguminosae. Johansen (1950) treated Leguminales as an Order that included three families Gaesalpiniaceae, Mimosaceae and Papilionaceae (Fabaceae). Lawrence (1951) accepted Mimosaceae, Caesalpiniaceae, and Lotoideae as sub-families of the family Leguminosae. Rendle (1925 ) considered Leguminosae as family com prising of three sub-families viz., Miraosoideae, Caesalpinoideae and Papilionatae. Metcalfe and Chalk (1950) treated Mimosaceae, Caesalpiniaceae and Papilionaceae as the families of Leguminosae. From the anatomical data they considered Mimosaceae as least specialised and Papilionaceae as highly specialised. But the position of Caesalpiniaceae is intermediate between the two. The structure of wood has been held to be fairly diagnostic in seggregating these three sub-families (Metcalfe and Chalk, 1950). It is also suggestive of the degree of specialisation and therefore of phylogenetic sequence. Mimosoideae is held to be least highly specia lised in this regard and the Papilionatae the most highly specialised. Dnyansagar (1956) discussed the status of Leguminosae. According to him Leguminosae should be treated as an Order and not a family. In order to support his views, he (Dnyansagar, 1956) gave embryological, cytological and anatomical evidences and considered Mimosaceae and Caesalpiniaceae as families but suggested that Papilionaceae being a heterogeneous group shoulc further be divided into more than one family. Takhtajan (1969) recognised three families, viz., Mimosaceae, Caesalpiniaceae and Fabaceae of the Order Fabales and used the word 'Fabales' for Leguminales. i On the basis of cytological evidences, many cytologists tried to consider the relationships in Leguminosae. Senn (1938, 1943) tried to trace the relationships between Mimosaceae, Caesalpiniaceae and Papilionaceae. However, he was not successful in doing so on account of the in adequate cytological work in Mimosaceae and Caesalpiniaceae. Atchinson (1947, 194^, 1951) studied the chromosome numbers of about II4 species of Leguminosae. According to her Mimosoideae is the most prim.itive of the three families and Papilionatae is the highly advanced sub-family. The flower structure and basic chromosome numbers suggested the link of Caesalpinoideae with Podalyrieae. Perhaps all three sub-families arojjse from similar ancestral proto types, but the prototypes were not found in the living representative and the indisputable link between the three sub-families was the poa character. Thus delimited, the family Leguminosae has enjoyed a more or less, constant position and stable status. Taxo- nomists are in agreement in placing the family unaer Resales (Bentham and Hooker, 1862-1883; Taubert, 1894; Bessey, 1915; Rendle, 1925; Engler and Uiels, 1936; Lawrence, 1951; Cronauist, 1968; Takhtajan, 1967, 1969) with obvious affinities with Connaraceae (Bentham and Hooker, 1862-1883; Bessey, 1915) of Chrysobalanaceae of the Rosaecae. Hutchinson (I964) raisea the status of the family to an \) ordinal rank Leguminales, but Takhtajan (1967, 1969) and Gronquist (1968) maintained its family rank under Resales. le' reTative positSn of the three s'uB-families or the families comprising the family Leguminosae or the Order Leguminales respectively with an obvious indication of Phylogenetic sequence, has been a matter of some dispute. It is of interest to read Bentham (Bentham and Hooker, 1^62-1^^3) and Hutchinson (1964) in this connection (Bentham and Hooker, 1852-1^^3) wrote about Leguminosae- "A vast family (Orders), very natural, divided into three sub families (Sub-Ordinatus) by sufficiently well defined characters." Amongst so many species, there are very few which are ambiguous between the Papilionaceae and Caesal piniaceae and between the later ana the Mimosaceae. Hutchinson (1964), however comr'ients: "it is merely a matter of opinion or conscience (or even of prejudice] ) whether Caesalpiniaceae should be treatea a separate family from Mimosaceae and Fabaceae (Papilionaceae) or all three regarded as sub-families of Leguminosae." It is a fallacy to assume that all of this group have the fruit - 'a legume', very many have not. Botanists fortunately are not hide bound by rules in such matters and are free to please themselves. No one is correct in such cases. Most of the authors have considered Mimosoideae as the relatively primitive taxon (Tauburt, 1894; Bessey,

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