Morphology of Some Species in the Subfamily Papilionoideae

Morphological study of ten species in the subfamily Papilionoideae was carried out with the view to documenting diagnostic characters that would distinguish or group the species. The species studied belong to four tribes, namely: tribe Desmodieae – Desmodium tortuosum (Sw.) DC., Desmodium scorpiurus (Sw.) Desv., Desmodium adscendens (Sw.) DC., tribe Phaseoleae – Cajanus cajan (L.) Millsp., Calopogonium mucunoides Desv., Centrosema molle (Mart.) ex. Benth., Mucuna pruriens (Linn.) Walp., Vigna unguiculata (Linn.) Walp., tribe Crotalarieae – Crotalaria retusa Linn., tribe Robinieae – Gliricidia sepium (Jacq.) Walp. Qualitative and quantitative traits which had not been documented in previous works, especially in Nigeria, were studied. These include plant life span; leaf/leaflet apex, base, margin and pubescence; stem type, colour, shape and pubescence; sepal colour and pubescence; nature of margin of petal standard and presence or absence of pedicel; fruit colour, pubescence, tip and shape; seed colour, shape, surface and presence or absence of prominent hilum on the seed; number of seeds per fruit; pedicel length; length and width of petal standard, keel and wing. Characters of taxonomic value documented in this study were leaf type, leaf shape, leaf base, petiole type, stem type, seed shape, petal standard length, petal keel length and petal wing width. Data were subjected to one way analysis of variance using Duncan’s multiple range test. It was noted that the important characters that can be used in establishing taxonomic relationship in the sub-family Papilionoideae were leaf type, leaf shape, leaf base, petiole type, stem shape, petal colour, petal margin and seed shape.


Introduction
The subfamily Papilionoideae belongs to the family Leguminosae.The subfamily is sometimes recognized as a separate family Papilionaceae.The species of this subfamily are generally identifiable by their characteristic papilionaceous (butterfly-like) flowers (ILDIS, 2005;Cullen et al., 2011).Papilionoideae is the largest group of legumes, with about twothirds of all the genera and species of the family Leguminosae.The homogenous subfamily is also the most widespread, generally distributed throughout the world; it is most numerous and extending further into warmer temperate regions compared with the other two subfamilies, Caesalpinoideae and Mimosoideae, in Leguminosae (Hutchinson and Dalziel, 1958;Gurcharan, 2004;Duane and Paul, 2012).The subfamily consists of about 475 genera and nearly 14,000 species, grouped in 14 tribes (APG, 2012;Duane and Paul, 2012) out of which about 335 species were recorded in Nigeria (Hutchinson and Dalziel, 1954).The members of subfamily Papilionoideae are predominantly herbs or herbaceous climbers; sometimes they are erect or climbing shrubs, trees or lianas (Datta and Mukherji, 1952;Hutchinson and Dalziel, 1958;Watson and Dallwitz, 1999;Gurcharan, 2004;ILDIS, 2005).It is an extremely important subfamily and finds a wide range of usefulness (Datta and Mukherji, 1952;ILDIS, 2005).
Most plants are classified based on their external morphological structures.The morphology and ontogenies of taxa are important for intra-generic systematics (Sayantan and Amal, 2004).Alexander (2004) presented an illustrated survey of abaxial leaf surface of 22 Desmodium species found in North Carolina and a diagnostic key to facilitate the identification and teaching of the species.He reported that Desmodium Desv.(Papilionoideae) is perhaps the most difficult genus among Carolina legumes.El-Gazzar et al. (2013) recorded 81 morphological characters for 226 species and intra-specific taxa belonging to 75 genera representing 21 of the 32 tribes currently recognized in the subfamily Papilionoideae, to know the extent to which the currently accepted classification of the subfamily by Polhill and Raven (1981) would withstand the test of numerical analyses.The authors concluded that the currently accepted circumscription and inter-relationships among the disrupted tribes and genera of Papilionoideae are in need of much more detailed investigation.
A search in the literature also shows that the information about the comparative morphology of most species in the subfamily Papilionoideae, especially those found in Nigeria, is scanty.This study therefore aimed to document the morphological traits of taxonomic value in the species studied.
All plant species were collected from different locations in Ile-Ife, latitude 07º 30'N and longitude 04º 40'E, Osun State, Nigeria.
Qualitative data observed and recorded were plant habit; plant life span; leaf type; leaf/leaflet shape, base, apex, margin, colour, pubescence; stem type, colour, shape, pubescence; presence or absence of stipule; inflorescence type; sepal aestivation, colour; standard petal margin; fruit type, segmentation, indentation or ribbing; fresh fruit colour; dry fruit colour; fruit shape, tip shape; seed shape and colour; presence or absence of depression on the seed; nature of seed surface; hilum prominent or not prominent.
Quantitative data taken were leaf length and width; petiole length; fruit length and width; number of seeds per fruit; pedicel length; petal standard length and width; petal keel length and width; petal width length and width.
Quantitative data generated from this work were subjected to one -way analysis of variance using Duncan multiple range test to show significant differences.Simple descriptive statistics from SPSS analysis were also used to calculate the minimum, maximum, means and standard error of means for each trait.

Results
The qualitative and quantitative traits of the species studied are hereby presented.They are summarised on Tables 1 -3, whereas descriptive terminologies used are according to Metcalfe and Chalk (1979).
Photographs of the diagnostic morphological traits of the studied species are presented on Figs. 1 -10.
Fruit: lomentum, segmented, segment orbicular, deeply indented on both sides twisted, obtuse at apex, 2.30 -3.00 cm long and 0.30 -0.40 cm wide, green with reddish brown pattern when fresh, brown when dry, pubescent, one row of seed per fruit (Fig. 1G and Fig. 1I).
Fruit: lomentum, segmented, slightly indented on both sides, cylindrical, obtuse at apex, 2.10 -4.30 cm long and 0.20 cm wide, light green when fresh, brown when dry, pubescent, one row of seed per fruit (Fig. 2I and K).
Fruit: lomentum, segmented, deeply indented on one side, short aristate at apex, 0.80 -2.40 cm long and 0.25 -0.35 cm wide, deep green when fresh and brown when dry, flat, pubescent, one row of seed per fruit (Fig. 3H and J).
Fruit: legume, obtuse at apex, sickle shape 8.40 -8.80 cm long and 2.10 -2.30 cm wide, rusty brown when fresh, brown when dry, pubescent -densely clothed with rusty stinging hairs, one row of seed per fruit (Fig. 4C and D).

Discussion
Many authors have stressed morphological characters as taxonomic tools.These include Hutchinson and Dalziel (1958), Terrel and Winters (1974), Isawumi (1985), Adedeji and Illoh (2005) and Adedeji (2005Adedeji ( , 2006)).El-Gazzar et al. (2013) reported that the only common feature of all classificatory systems of the Papilionoideaeto date is the recognition of tribes and sub-tribes on the basis of a limited range of floral traits, with greater emphasis on petal morphology and stamen arrangement.Such a limited number of characters were used often singly to distinguish between chunky assemblages of genera.
In the current study, additional traits, further from those reported by Hutchinson and Dalziel (1958), which are quite diagnostic for the taxonomy of the subfamily, were herein reported.Additional traits which previous researchers have not reported include life span; leaf/leaflet apex, base, margin and pubescence; stem type, colour, shape and pubescence; sepal colour and pubescence; nature of margin of petal standard and presence or absence of pedicel; fruit colour, pubescence, tip and shape; seed colour, shape, surface and presence or absence of prominent hilum on the seed.
The morphological characters used for this study are sufficient in establishing the relationships among the species of Papilionoideae studied.Thirty eight qualitative and thirteen quantitative traits employed have been reported in the current study.Joelri et al. (2011) reported in their work on Crotalaria in South India that leaves, simple or compound, is a major feature in developing taxonomic key based on morphological characters.In this study, leaves were compound except in the case of Crotalaria retusa, which was the only species with simple leaves; this can be used to delimit it from the other species.Gliricidia sepium (Tribe Robinieae) which was the only species that had compoundonce pinnate leaves, can further be separated from the other species which had compound-trifoliate leaves.This also justifies its separation from other tribes.Rahman and Rahman (2012) used leaf shape to group Desmodium alatum and Desmodium auriculatum together and separated them among 14 species of Desmodium studied.Adedeji (2006) also reported that the shape of the upper leaves can be used in the taxonomy of the genus Emilia.Leaf shape was also used by Joelri et al. (2011) to discriminate Crotalaria verrucosa from the rest of Crotalaria species studied in South India.
In the hereby study, leaf/ leaflet shapes can also be used to delineate the species of Desmodium from one another and other species studied.Leaflets of Desmodium tortuosum were ovate, those of Desmodium scorpiurus were elliptic, while those of Desmodium adscendens were obovate in shape.Leaflets of Mucuna pruriens and Calopogonium mucunoides were wide ovate to wide elliptic.Crotalaria retusa in the tribe Crotalarieae was the only species with oblanceolate leaf shape and this also delineated it from other tribes.
The stem of Crotalaria retusa was cylindrical in shape, with vertical ridges, while that of Cajanus cajan was cylindrical, with distinct angles.Desmodium tortuosum was the only species that had ringed stem.Desmodium scorpiurus had triangular shaped stem, while that of Centrosema molle was twisted.Crotalaria retusa was the only species with hollow stem, whereas all others had solid stems.These characters of stem can be used to delimit the taxa studied.
Variation also occurred within the petal colour among the species.However, all Desmodium species studied had pinkish purple flowers.This supports their grouping into the same tribe Desmodieae.Joelri et al. (2011) separated Crotalaria laburnifolia and Crotalaria pallida from other Crotalaria species studied using reddish brown stripes at the keel petals.In this study, bright yellow petals with reddish brown veining on the standard were recorded for Cajanus cajan and Crotalaria retusa.This can be used to group them apart; even more, standard petal of Cajanus cajan was indented at margin and this can be used to separate it from Crotalaria retusa and other species which were entire at margin.Daiane et al. (2014) reported the importance of the form of loment margin as identification key for Desmodium species studied in Santa Catarina, Brazil.Fruits were legume except in Desmodium species from the tribe Desmodieae, which were lomentum, and this delimited the tribe from other tribes studied.However, Desmodium adscendens can be separated from other Desmodium species because its fruit were deeply indented on one side only, while others were indented on both sides.There were variations also in the shape, colour and surface of seeds.These characters can also delimit the species.Crotalaria retusa had reniform (kidney-shaped) seeds, Desmodium scorpiurus was cylindrical, while others were bean shaped.This can be of taxonomic value.
The current study reports that Crotalaria retusa was the only species with simple leaves, oblanceolate leaf shape, cuneate leaf base, sub sessile leaves, hollow stem and reniform seed shape.These distinct characters justify the delimitation of Crotalaria retusa in the tribe Crotalarieae from the other tribes in the sub-family.Quantitatively, Desmodium adscendens had the lowest leaf size (both length and width).Petiole length of the pair Mucuna pruriens and Calopogonium mucunoides, as well as the pair Centrosema molle and Gliricidia sepium were not significantly different.These characters can be used to separate these taxa from other species.Desmodium tortuosum had the longest pedicel length.
As regards petal values, petal standard length, petal keel length and petal wing width are more useful in separating or delineating the genera and tribes than the values for leaf length and width, petiole length, fruit length and width, number of seeds per fruit and petal values were not significantly different within the three species in the genus Desmodium, but were significantly different between the other genera studied.However, the leaf length, petiole length, fruit length, number of seeds per fruit and pedicel length values can be used to delineate the species within the genus Desmodium as the values were significantly different within each character for the Desmodium species.

Conclusions
This study hereby reported that the important characters that can be used in establishing taxonomic relationship in the sub-family Papilionoideae are leaf type, leaf shape, leaf base, petiole type, stem shape, petal colour, petal margin and seed shape.

Table 1 .
Summary of the qualitative morphological traits of the studied species of the subfamily Papilionoideae

Table 1 .
Summary of the qualitative morphological traits of the studied species of the subfamily Papilionoideae (Contd) Key: + : Present; -: Absent; ± : Sub sessile

Table 1 .
Summary of the qualitative morphological traits of the studied species of the subfamily Papilionoideae(Contd)

Table 1 .
Summary of qualitative morphological characters of the species of the subfamily Papilionoideae studied (Contd)

Table 2 .
Minimum, mean, standard error of mean and maximum values of the quantitative morphological traits of Papilionoideae species studied Key: Min=Minimum value, Max=Maximum value, S.E.M=Standard error of mean

Table 3 .
Species grouping from Duncan's multiple range test based on morphology