Abstract: Observations on the vegetative and floral morphology of eight species of Vigna namely V. ambacensis, V. gracillis, V. racemosa, V. reticulata, V. subterranea, V. triloba, V. unguiculata and V. vexillata are presented. The results of the vegetative characters showed that V. ambacensis and V. gracillis are creeping herbs while others are climbing herbs. The leaf texture of all the taxa are rough except in V. racemosa with smooth leaf texture and the leaf shape of V. reticulata and V. vexillata are lanceolate, linear in V. racemosa but ovate in others. V. reticulata has the longest leaf while V. unguiculata has the widest leaf. The floral symmetry is zygomorphic in V. ambacensis and V. triloba but actinomorphic in others. V. vexillata has the longest pod while V. subterranea has the widest pod. The seed number per pod is numerous in V. reticulata, V. triloba and V. vexillata but ranges from 4-10 in others. The significance of these characters in the taxonomy of these taxa was discussed in view of the perceived similarities in structural and reproductive biology of these taxa.
INTRODUCTION
The genus Vigna belongs to the family Leguminosae-Papilionoideae. The Leguminosae-Papilionoideae are mostly herbs but include also shrubs and trees found in both temperate and tropical areas (Isely, 1982). They comprise one of the largest families of flowering plants, numbering some 400 genera and 10,000 species (Smartt, 1980). They are dicotyledonous plants bearing pods with one or more seeds whose pods dehisce along both dorsal and ventral sutures (Rachie and Roberts, 1974).
Morphologically, Vigna species are mostly shrubs, herbs or lianes; They may be resinous or not resinous. Majority of them are normal plants while others are switch-plants with the principal photosynthesizing functions transferred to stems and leaves (Tindall, 1968). The leaves are well developed or much reduced. The herbs are annual, biennial or perennial with neither basal nor terminal aggregations of leaves. They are self-supporting, epiphytic or climbing. The climbers are stem twiners or tendril climbers via stem or leaf tendrils or scrambling via hooks. The twiners are twining clockwise or anticlockwise as in Phaseolus and Wisteria G. Don. (Rachie and Roberts, 1974). Some are hydrophytic, mesophytic or xerophytic. Others are heterophyllous with bipinnate juvenile and phyllogineous mature foliage leaves. The leaves are usually evergreen to deciduous, minute to large, alternate, opposite to whorled, spiral to distichous, petiolate to sessile; and aromatic to non-aromatic (Daniel, 1960). They can also be herbaceous, leathery, membranous or modified into spines, non-sheathing, gland-dotted, aromatic or not, with normal orientation. The leaves can be compound, simple pulvinate, epulvinate, unifoliolate, ternate, pinnate (commonly, either pari-or imparipinnate), palmate (commonly bipinnate or bifoliolate). The leaves are nearly always stipulate but few are exstipulate. The stipules could be intrapetiolar, scaly, leafy, spiny, caducous, persistent and represented by glands. The leaves also lack persistent basal meristem (Skerman et al., 1988; Daniel, 1960; Aziz and Shah, 1966). The calyx has two upper teeth which are free or connate. The base of the calyx is appendicular with inflexed auricles. The wings are falcate-obovate and shorter than the standard. The keel is truncate or beaked at the tip. The upper stamen is free while others are connate. The anthers are uniform. The ovary is sessile and multiovulate. The style is filiform, dilated upwards and longitudinally bearded on the inner side upwards. The stigma is very oblique. The pod can be linear, straight, recurved, subterete with two valves filled within the seeds. (Daniel, 1960; Burkill, 1995).
The use of vegetative and floral morphology in the systematic grouping, characterization and classification of different taxa is no more a rare event. For example, Edeoga et al. (1998) used vegetative and floral characters to classify eight species of Dioscorea. According to them, the variation in the floral morphology seen in flowers, fruits, seeds and floral formulae of the investigated Dioscorea species, is in agreement with the earlier research findings that emphasized that the inflorescence are very variable in form and that the flower construction is equally variable (Dahlgren et al., 1985; Rudall et al., 1995).
Despite the numerous economic and agronomic importance of the Vigna species, there is absence of clear taxonomic criteria especially in vegetative and floral morphology to delineate these taxa. The objective of this study therefore is to present the vegetative and floral characters of the eight Vigna species that could be used for the systematic characterization of these species.
MATERIALS AND METHODS
The studies were made on living and herbarium materials (Vigna species) identified with standard herbarium specimens collected from Forest Herbarium, Ibadan (FHI), University of Ibadan Herbarium (UIH), International Institute for Tropical Agriculture (IITA) Onne Station Port Harcourt, Rivers State and National Root Crop Research Institute (NRCRI) Umudike, Abia State. The living species were collected from some parts of Eastern Nigeria such as Imo, Rivers, Abia, Ebonyi, Enugu, Anambra, Bayelsa, Akwa Ibom and Cross River states (Table 1). This study was conducted at the Science Laboratory of Michael Okpara University of Agriculture, Umudike Umuahia, Abia State Nigeria in October, 2005.
Morphological studies: Morphological studies were carried out on the mature living and herbarium specimens. Thirty mature leaves from the middle portion of the plant were collected for this study. These leaves were collected from different Vigna species from different locations such as Amakaohia, Omaogwa, Ndioro, Abakaliki, Nsukka, Awka, Ishielu, Uyo and Ikot Ekpene (Table 1). The length and width of the leaves were measured using a 30 cm rule. This was done by spreading the middle leaflet on a flat surface of a laboratory bench. For the width, the same median leaflet was chosen to avoid being biased. Altogether 30 mature leaves were measured for each of the taxa. Data collected were analysed statistically and bar charts drawn using a computer. The seed number per pod was obtained by counting the number of seeds in the longest pod so as to ensure consistency. Photographs of the herbarium specimens were taken using ordinary camera (Fig. 1 and 2).
RESULTS
Hutchinson and Dalziel (1958) and Burkill (1995) have described the morphology (vegetative and floral) of these taxa to some extent. However, a more detailed description of the structures of these plants based largely on fresh specimens, that are of taxonomic interest is presented in this section.
| Table 1: | List of Vigna species from which fresh material was used |
| *MOUAUH =Michael Okpara University of Agriculture Umudike, Herbarium | |
| Table 2: | Vegetative characters of the eight vigna species studied |
| Fig. 1: | (A-C) Habit of the Vigna species studied. (A) V. gracillis, (B) V. reticulata, (C) V. vexillata Note: The differences in shapes of leaves of these taxa |
| Fig. 2: | (A-C) Habit of the Vigna species studied. (A) V. unguiculata, (B) V. ambacensis, (C) V. racemosa, Note: The differences in shapes of leaves of these taxa |
| Table 3: | Floral morphology of the eight Vigna species studied |
The results of the vegetative features of the eight Vigna species studied showed that V. gracillis and V. ambacensis are creepers while V. vexillata, V. reticulata, V. triloba, V. unguiculata, V. racemosa and V. subterranea are climbers (Table 2, Fig. 1 and 2).
The stem bark of V. triloba, V. unguiculata and V. subterranea are smooth while those of V. reticulata, V. vexillata and V. ambacensis are hairy. The leaf texture of V. racemosa is smooth and differs from other seven species that are rough. V. racemosa has linear leaf shape, while V. gracillis, V. tribola, V. unguiculata, V. ambacensis and V. vexillate have lanceolate leaf-shape. The leaf apex is attenuate in V. racemosa and V. vexillate but acute in the other six species. The leaf base is obovate in V. gracillis and V. ambacensis, round in V. triloba, V. racemosa and V. subterranea, obtuse in V. unguiculata and attenuate in V. reticulata and V. vexillata. V. reticulata has the longest leaf while V. unguiculata has the widest leaf. Also, V. ambacensis, V. unguiculata and V. vexillata have leaf lengths that are approximately the same (Table 2, Fig. 1 and 2).
The floral morphology (Table 3) showed that the pedicel of V. vexillata and V. racemosa are very short compared to those of other six species that are short. The floral symmetry of V. triloba and V. ambacensis are zygomorphic whereas the other six species are actinomorphic. V. ambacensis is distinct with solitary type of inflorescence compared to axillary raceme in V. reticulata and V. unguiculata, raceme in V. gracillis, V. vexillata, V. triloba, V. racemosa but V. subterranea. The sepals and petals are fused in V. vexillata and V. racemosa and free in the other six species studied. V. ambacensis is distinct with oblong fruit shape, compared to linear fruit shape that characterized V. reticulata, V. vexillata, V. triloba and V. racemosa, ovoid fruit shape in V. gracillis, V. unguiculata and V. subterranea. The pod length of V. racemosa and V. triloba are approximately the same (Table 2) and that of V. unguiculata and V. vexillata are approximately the same indicating that these species can be distinguished from others using this character. V. unguiculata is distinct having the widest pod compared to others (Table 2).
DISCUSSION
The characteristics vegetative and floral features of the eight Vigna species are summarisd in Table 2 and 3. The outcome of this investigation separated the species into climbing and creeping herbs and established zygomorphic and actinomorphic types of symmetry among the taxa. The longest and the widest pod lengths of V. vexillata and V. subterranea is reported for the first time in these species. The variation in the vegetative and floral morphology as seen in the flowers, fruits, seeds, leaves ,pods and other vegetative and floral characters of the investigated Vigna species is in agreement with some of the earlier research findings of Daniel (1960) and Hutchinson and Dalziel (1958) whereas others are added data for easy identification and characterization of these taxa. These data from the floral and vegetative morphology of the Vigna species investigated, however, present some important characters that could be exploited in improving the characterization of the Vigna species.