Important Morphological Characters in Several Species of Cassiinae ( Leguminosae ) in South-Western Nigeria

Macromorphological characters of some species of Cassia L. emend. Gaertner, Senna Miller and Chamaecrista Moench occurring in South Western Nigeria were studied. The aim was to search for stable, distinctive and diagnostic characters for the identification of these genera and their species. Qualitative characters were noted and recorded while quantitative observations were done by the use of a metric ruler and the measurements were taken to the nearest centimeters. The habit ranges from all shrubs in Senna, shrubs and herbs in Chamaecrista while the Cassia species studied are all trees. The shape of the leaflet apex varies in both Senna and Cassia species, while it is distinctly mucronate in Chamaecrista genus. Occurrence of foliaceous stipule in the genus Chamaecrista clearly separates it from Senna and Cassia, which are completely exstipulate. In general, other characters such as number of leaflet pairs, length and width of leaflets, leaflet base, and number of leaflets lateral nerves revealed generic distinctions. Others include the degree of hairiness in sepals, petals shape, types of inflorescence, fruit shape and fruit length. The attributes that delimits the species are mainly quantitative. The results of this investigation suggest macromorphological characters that clearly enhance the taxonomy of these genera and their species and they can be subsequently employed in their delimitation.


Introduction
Prior to the work of Irwin and Barneby (1981), the genus Cassia used to be a very large genus that comprises of about 500 to 600 species (Airy-Shaw, 1973).The genus ranks among the 25 largest genera of the dicotyledonous plants (Irwin and Turner, 1960).Bentham (1871) and Bentham and Hooker (1876) did a lot of work in the general classification of this genus, these two works recognizes that there are three subgenera in these genus, vis: Cassia, Senna and Lasiorhegma.In West Africa, the genus contains about 22 indigenous species apart from those introduced or cultivated (Hutchison and Dalziel, 1958).There is a great diversity of habit within the genus ranging from trees approaching 34 m in height to prostrate annual herbs.Some members of the genus are important ornamentals e.g.Cassia siamea (Olorode, 1984), this plant is used for afforestation programmes in drier areas.Other members of the genus could be useful as commercial timbers and a great number of them have been reported to be of great use in herbal medicines especially as laxatives and in the treatment of skin diseases (Ayensu, 1978;Olorode, 1984;Di Stasi et al., 1989).
Paripinnate compound leaves and many leaflets characterize the genus; however, Oloruntoba (1984) reported a simple leaf accession to which Adebowale (2000) suggested that the accession is probably a product of recent reverse mutation event in Cassia occidentalis because of its restricted distribution.The flower is one of the constant characters found in this genus despite its great diversity of form.The flowers are hermaphroditic and generally monocarpellate, zygomorphic and arranged in conspicuous axillary or terminal racemes (Hutchison and Dalziel, 1958).The stamens are ten in number and they are heteromorphic, some may be reduced to staminodes (Hutchison and Dalziel, 1958).The fruit that is many seeded is a pod of varying lengths that may be from 3 cm to 1 m and may assume different shapes and sizes (Olorode, 1984).
Interestingly in 1981, Irwin and Barneby subjected the genus into some nomenclatural and taxonomic changes that eventually led to the revision of the genus Cassia (Irwin and Barneby, 1982) and splitting of the genus into smaller genera viz : Cassia, Senna and Chamaecrista. However, Lock (1988) observed that series of problems have arisen due to this name changes because many taxonomists especially on the African flora may prefer to continue to use Cassia in its broad sense, which would be acceptable if there was no overlap between floras of Africa and South America.However, many species in this genus are endemic in the tropics because of dispersal or deliberate introduction as exotic plants, this will further results into confusion, as several species will be given different names in different continents (Lock, 1988).Additional information on this very important group of plants, which will provide insights into detailed diagnostic characters that would be of help to taxonomist after this new classification are scanty.Therefore this study aims to provide a comprehensive description of the macromorphological characters of the new Cassia, Senna and Chamaecrista species, thereby adding more to the scanty information on the morphology habit is mostly perennials, shrub, suffrutescent usually about 4.5 m high or more.The stem is greenish at top and woody below, glabrous; petiole is terete 2.6-10 cm long (Tab.2), connecting the leaflets.Leaf is paripinnate, exstipulate, leaflets about 5-12 pairs, arranged oppositely along a transverse ridge.The leaf is oblong to obovate at the base and the apex is mostly rounded, sometimes emarginate apex is found.The margin is mostly entire 6-18 cm long, 4.3-16 wide (Tab.2).The venation shows primary veins that are straight in course with lateral veins been around 9-23 per leaflet mostly alternate some are opposite.The inflorescences are a terminal raceme (Tab.3), compact, conspicuous with elliptic bracts ranging from 2.5cm long and 1.2 cm wide.The pedicel is greenish, sparsely pubescent about 0.6 cm long while the sepal is about 1.3-1.7 cm long and 0.4-0.6 cm wide glabrous, yellowish, connate at base pentamerous, lanceolate.Petals are deep yellow, pentamerous, assymetrical about 1 cm long and 0.7 cm wide.The stamen is about 0.6 cm long, filament greenish brown, anther yellowish.Style is greenish about 1.3 cm long and the stigma dark brown.The fruit is a samaroid pod (Tab. 3), black when mature and dry, oblong in shape, 17-27 cm long and 1.4-2.0cm wide.
S. hirsuta L. (Fig. 1B) This is a weed commonly found near habitations, on roadsides, farmlands, wastelands as well as abandoned areas.They are shrub (Tab.2), suffrutescent, mostly up to 2 m high, mostly annuals sometimes biennial or perennial.The stem is greenish at the top and woody brownish base, densely pubescent.The petiole is mostly polygonal 3.5-5.8cm long.The leaf is paripinnate, exstipulate, leaflets arranged oppositely in 4-5 pairs, it is broadly lanceolate to ovate in shape, margin mostly entire, sometimes few minor serration present base acute, apex attenuate, 4.5-11 cm long, 2.6-5.2cm wide (Tab.2).The venation consist of primary veins that are straight in course with lateral veins in pairs ranging from 5-13 pairs per leaflets, mostly alternate, more prominent on the abaxial surface.Inflorescence is a raceme (Tab.3).The pedicel is greenish, pubescent 0.6-1.2cm long, sepals are greenish yellow, pentamerous, lanceolate densely pubescent 0.4-0.8cm long and 0.2-0.4cm wide, while petals is brilliant yellow, pentamerous, ovate to assymetrical, 0.7-1.6 cm long and 0.4-0.9cm wide.The stamen is about 0.5-1.3cm long, filament brown to dark brown, anther brownish yellow.The style is Greenish yellow, densely pubescent, stigma 1.5-2.3cm long dark to black in colour, curved at the apex.The fruit is a flat pod (Tab.3), yellowish brown, densely pubescent, about 17 cm long and 0.5 cm wide, apex acute.S. obtusifolia (L.) Irvin and Barneby (Fig. 1C) This is a weed commonly found along roadsides near habitations and wastelands.They are shrub, suffrutescent, mostly about 1.5 m high (Tab.2), annual, sometimes biennial.The stems are greenish at the top and brownish at of these genera and eventually their taxonomy.We equally hope that the outcome of this study would be employed along with other diagnostic features for proper identification and classification of these genera and their species as well as to justify or otherwise, the separation from the initial genus Cassia as defined by Bentham (1871) and Betham and Hooker (1876).

Materials and methods
Five species were selected from the genus Senna and they are: S. alata (L.) Roxb, S. hirsuta (L.) S. obtusifolia (L.) Irwin and Barneby, S. occidentalis (L.) Link and S. sophera (L.) Roxb.Three species were selected from the genus Chamaecrista namely C. kirkii (Oliver) Standley, C. mimosoides (L.) Greene and C. rotundifolia (Pers.)Greene, while two species from the genus Cassia were studied these are: C. fistula L. and C. siberiana DC.All the specimens were collected from different location within South-Western part of Nigeria (10 o 00ʹ N, 8 o 00ʹ E), an abridged listing of the specimens cited are shown (Tab.1), dried herbarium specimens of all the species were also studied morphologically at the Obafemi Awolowo University Herbarium (IFE) and the herbarium at the Forest Research Institute of Nigeria, Ibadan (FHI).
The habit and habitat of each species were recorded.Qualitative morphological characters studied include: leaflet shape, base and apex, their margins, vein, petioles, fruit types, their shape and apex.Others characters studied include presence or absence of stipule, colours of petals, pedicel, epicalyx, sepals, style, filament, anther and stigma as well as the shapes of petals, sepals and epicalyx were also observed and recorded.Quantitative morphological characters measured include length and breadth of leaflets, length and diameter of fruits, petal, style and stamen lengths, this was done by the use of a metric ruler and the measurements were taken to the nearest centimeters.Counts were taken of the number of sepals, petals and epicalyx.Fresh materials collected in the field were pressed and processed immediately as voucher specimens and they were deposited at IFE herbarium after the photograph of a representative specimen of each species were taken and imported into Corel Draw 12 for presentation.

Results
The macromorphological features of each species are described in the following presentation, grouping them under their respective genera.

S. alata (L.) Roxb. (Fig. 1A)
The plant is found cultivated around habitations because of its medicinal value or found as weed growing in wastelands, abandoned lands and along roadsides.The (Key: + = present;-= absent) S. occidentalis (L.) Link (Fig. 1D) This is a common weed found near habitations, along roadsides as well as wastelands.They are shrub, suffrutescent up to 1.5 m tall (Tab.2), mostly annuals, sometimes they are biennials.The stem is greenish at the top and grayish to brown at the base, with glabrous surface.Petiole is polygonal 4.6-6.3cm long.The leaf is pinnately compound, paripinnate, exstipulate leaflets 4-5 pairs arranged oppositely, the top pair being the largest about 4.3-11.4cm long and 1.5-3.0cm wide, broadly lanceolate to ovate.The mar-or paired.Pedicel is greenish, pubescent 0.6-2.7 cm long.The sepal is pubescent, greenish yellow, connate at base, pentamerous, mostly ovate, about 0.5-1.0cm long and 0.4-0.7cmwide.The petal is pinkish-yellow, some brilliantly yellow, pentamerous, obovate few are assymetrical about 0.6-1.7 cm long and 0.5-1.0cm wide.Stamen is about 0.4-1.0cm long filament reddish brown, anther brown.Style is light green, about 1.5 cm long, stigma dark brown.The fruits are a brownish pod (Tab.2), polygonal in shape about 20cm long and 0.5 cm wide, apex acuminate.and mucronate at the apex and asymmetrical at the base, the margin is entire and the leaf is sparsely pubescent.Venation is actinodromous; perfect, basal and reticulate, primary vein is straight in course.The inflorescence is solitary (Tab.3); sometimes 2-3 flowers occur at the axil.Pedicel is greenish to brown, 1.0-1.4cm long, pubescent.Sepal is glabrous, 0.6 cm long and 0.1-0.2cm wide, greenish yellow in colour, pentamerous, lanceolate, and connate at the base.Petals are brilliantly yellow, 0.6 cm long and 0.3 cm wide, pentamerous, ovate in shape.Stamens are about 0.3-0.5 cm long, filaments; greenish yellow, while anther is dark brown.Style is about 0.6 cm long, greenish yellow stigma dark brown in colour.The fruit is a pod (Tab.3), 3.2-6.8cm long and about 0.4-0.6 cm wide, brownish to black in colour, greenish when young, flat, linear, oblong, slightly curved and densely pubescent.
C. mimosoides (L.) Greene (Fig. 1G) This is a weed commonly found along roadside, as well as in vegetations, farmland and grasslands, common on sandy soil.They are herbaceous (Tab.2) or low shrub; grow up to 1.5 m high or sometimes diffuse.The stem is greenish to brown and pubescent.The petiole is mostly round 0.3-0.5 cm long.Stipule is foliaceous, assymetrical in shape 0.6-1.3cm long and 0.2-0.4cm wide attenuate apex, truncate base, pubescent.Leaf is pinnately compound, paripinnate, leaflets 25-70 pairs oppositely arranged 0.3-0.7 cm long and 0.1-0.2cm wide, assymetrical, linear, obliquely acute and mucronate at the apex, assymetrical at the base, margin entire, they are sparsely pubescent (Tab.2).The venation is actinodromous, perfect, basal and reticulate, primary vein straight in course.Inflorescences are solitary (Tab.3); sometimes 2-3 flowers occur at the axil.The pedicel is greenish to brown, about 1.2-2.2cm long and they are pubescent.Sepals are glabrous, greenish yellow, pentamerous, connate at base, lanceolate, about 0.4 cm long and 0.1 cm wide.Petals are brilliant yellow, pentamerous, ovate in shape, about 0.4 cm long and 0.2 cm wide.The stamens are about 0.3 cm long; filament is brownish yellow while anther is dark brown.The style is greenish yellow, about 0.4 cm long, stigma dark brown in colour.Fruits are a pod, about 1.5-3.5 cm long (Tab.3) and about 0.3-0.5 cm wide, they are dark brown to black, greenish when young, linear, oblong, slightly curved and pubescent.
C. rotundifolia (Pers.)Greene (Fig. 1H) They are weed commonly found around habitations, especially growing within grasses on lawns, they are occasionally found in weedy environment, along road side and farmlands.They are herbaceous (Tab.2), prostrate, about 0.5 m long or more.The stem is greenish in colour, light brown at the base and pubescent.Petiole is round, about 0.3-0.6 cm long.The stipule is foliaceous, assymetrical in shape up to 0.7 cm long and about 0.4 cm wide, attenuate apex and cordate base pubescent.Leaf is pinnately compound, paripinnate, 1 pair leaflets are oppositely arranged, gin is entire, base acute, apex mostly attenuate sometimes acuminate (Tab.2).Venation consists of primary veins that are straight in course, the lateral veins are about 7-14 in pairs per leaf, and they are mostly alternate, more prominent on the abaxial.Inflorescences are a raceme (Tab.3), flowers are few in number, the pedicel is green, pubescent about 0.3-1.3cm long.Sepals are greenish-yellow sparsely pubescent, connate at base, pentamerous, lanceolate about 0.4-0.6 cm long and 0.1-0.3cm wide.The petal are brilliant yellow, pentamerous, asymmetrical in shape, about 0.5-0.7 cm.Stamen is about 0.6-1.2cm long, filament greenish -yellow, anther brownish yellow.Style and stigma are greenish up to 1.3 cm long, the stigma is dark brown.The fruit is a flat pod (Tab.2), dark-grey in colour about 8.4-13.6 cm long about 0.4 cm wide.
S. sophera (L.) Roxb.(Fig. 1E) A weed commonly found near habitation and farmlands, along roadsides, often found close to S. occidentalis.They are shrub (Tab.2), suffrutescent up to 1.5 m tall mostly annual, sometimes biennial.Their stem is glabrous, greenish at the top and brownish at the base.Petiole is mostly round about 4.6-5.8cm long.The leaf is pinnately compound, paripinnate, exstipulate, leaflets 6-9 pairs arranged oppositely, 4.1-7.3cm long and 0.8-1.7 cm wide, narrowly lanceolate (Tab.2), margin entire, base acute, apex attenuate, some are very acute.The venation consists of primary veins that is straight in course, lateral veins 8-12 pairs per leaflets, mostly alternate, more prominent on abaxial.Inflorescence is racemose (Tab.3), few-flowered.Pedicel is greenish yellow, sparsely pubescent 1.0-1.3cm long, sepals are shortly pubescent, greenish yellow connate at base; about 0.6 cm long and 0.4 cm wide, pentamerous and lanceolate.Petals are brilliant-yellow in colour sometimes they may be reddish yellow, pentamerous, assymetrical in shape about 0.8 cm long and 0.4 cm wide.Stamens are about 0.5-1.2cm long, the filament is yellowish, anther, is reddish-yellow.The style is light green, about 1 cm long, while the stigma is dark to brown in colour.The fruit is a flat pod (Tab.2), dark green in colour about 8 cm long and 0.4 cm wide.

Genus Chamaecrista
C. kirkii (Oliver) Standley (Fig .1F) This is a weed that is commonly found on vegetations, lawns, farmlands and along roadsides common on sandy soils.They are erect shrub (Tab.2), subwoody, grow up to 1.5 m high.The stem is greenish to reddish brown and they are pubescent.The petiole is mostly round about 0.3-0.5 cm long.Stipule is foliaceous, assymetrical in shape, about 0.4-1.0cm long and 0.1-0.2cm wide, attenuate at the apex, and base is truncate in shape, pubescent.The leaf is pinnately compound (Tab.2), paripinnate, leaflets, 16-38 pairs, oppositely arranged 0.8-1.3cm long and about 0.2 cm wide, asymmetrical, oblong-linear, obliquely acute about 3.4-4.8cm long and they are pubescent.Sepals are pubescent, greenish yellow, connate at the base, pentamerous, lanceolate, about 0.8-1.3cm long and 0.4-0.6 cm wide.Petals are bright yellow, pentamerous, elliptic in shape about 2.1-2.9 cm long and 1.0-1.8cm wide.Stamens are about 2.0-5.2cm long; filaments are yellow while the anther is brown.Style is greenish, about 4.6-5.8cm long, stigma is also greenish.Fruits are a pod, black, could be straight, sometimes curved (Tab.3), rod-like or round in shape, apex is acuminate about 42-76 cm long and about 1.3 cm wide.

Discussion
The morphological characters studied in this work correspond largely with those of Hutchison and Dalziel (1958).Watson and Dallwitz (1993) used morphological features in characterizing some genera in Leguminosae-Calsalpinioidea and tribe Swartzieae.However, few salient morphological characters that were not recorded by these authors and which may enhance the taxonomy of these genera and species in Nigeria have been established in this study.The habit encountered in the three genera are variable, members of Senna genus are all shrubs in the five species studied, though Lock (1988) presented the genus as consisting of trees, shrubs or herbs.The Chamaecrista genus consist of shrubs and herbs, C. kirkii and C. mimosoides are shrubs while C. rotundifolia is herbaceous, but the Cassia genus are all trees, this results correspond largely with the previous work carried out by Lock (1988).All the species of the three genera are mostly perennial, though there may be combinations of annual, biennials and sometimes perennial habit in the genus Senna, where S. hirsuta, S. obtusifolia, S. occidentalis and S. sophera integrate the three habits.The only purely perennial in the genus is S. alata.In the Chamaecrista genus, all the species are mostly annuals and sometimes biennials while all Cassia species are perennials.
The shape of the leaflet apex varies in the species of Senna, while it is rounded and sometimes emarginated in S. alata, it is attenuate in S. hirsuta, S. sophera and S. occidentalis, although acuminate apex sometimes occur in S. occidentalis while in S. obtusifolia the apex is mainly obtuse.In the genus Chamaecrista, the leaflet apices are distinctly mucronate whereas in the Cassia genus acute apices are found in C. fistula while it is obtuse in C. siberiana.Interestingly, the leaflet base is quite delimiting for the three genera, it is acute in the species of Senna except in S. alata where it is rounded.Assymetrical base is found in all the three species of Chamaecrista studied, however, there are variations with the Cassia genus with C. fistula being acute while C. siberiana is obtuse.
Recently, Kahraman and Doğan (2010) used leaf morphological characters to separate two closely related species of Salvia in Turkey.Hitherto leaflet numbers which are found taxonomically useful in this study was not been obovate, assymetrical at base, apex mucronate, 0.6-2.0cm long and 0.4-1.2cm wide, the margin is entire and the leaf is pubescent (Tab.2).Venation is actinodromous, basal, perfect and reticulate, primary vein straight in course.Inflorescences are axillary, solitary, or occasionally paired (Tab.3).Pedicel is greenish, about 2.6-3.7 cm long, glabrous.Sepals are glabrous, greenish yellow, pentamerous, 0.3 cm long and 0.1 cm wide.Petals are yellowish, pentamerous, and ovate in shape, about 0.3 cm long and 0.2 cm wide.Stamens are about 0.3 cm long; filament is greenish yellow, while anther is yellowish.Style is greenish yellow, about 0.3 cm long, while stigma is pale yellow.The fruit is a pod, dark brown or black brown, linear to oblong (Tab. 3), slightly curved, about 2.0-3.2cm long and 0.2-0.4cm wide.

Genus Cassia
C. fistula L. (Fig. 1I) This is an ornamental plant used as vegetation cover, for shade and decoration.They are Tree, perennial, erect around 15 m tall (Tab.2).The stem is brownish to grey, greenish when young and glabrous.Petiole is round, 6.5-8.3 cm long.The leaf is pinnately compound, paripinnate about 7.6-18.2cm long 4.2-8.3cm wide, exstipulate, leaflets are arranged oppositely, margin is entire, ovate in shape while the shape of the base and apex is acute (Tab.2).Venation pattern shows that the primary vein is straight in course, lateral nerves are about 12-24 pairs per leaflet, alternate mostly, more prominent on the abaxial surface.Inflorescence is racemose-Corymb (Tab.3).Pedicel is greenish in colour, sparsely pubescent, long 5.6-12.3cm long.Sepals are pubescent, greenish yellow, connate at base, pentamerous, lanceolate about 0.4-1.2cm long and 0.3-0.6 cm wide.Petals are brilliant yellow, pentamerous, elliptic in shape 1.6-3.2cm long and 1.4-2.1 cm wide.Stamens are about 2.2-3.6 cm long; filaments are greenish yellow while anthers are brown.Style is greenish, about 3.6-5.1 cm long with greenish stigma.Fruit is a pod, black in colour, mostly straight to curved (Tab.3), rod-like or round in shape, the length varies could be as long as 80 cm and 1.6 cm in width.
C. siberiana DC. (Fig. 1J) This is an ornamental plant usually planted for shade and decoration.They are trees, perennial, usually about 15 m high (Tab.2).The stem is brownish to grey in colour.The petiole is mostly round, about 3-5 cm long and 0.1-0.4cm wide.Leaf is pinnately compound, paripinnate, exstipulate, about 4.3-8.4cm long, 2.4-4.3 cm wide, the leaflets are in 5-8 pairs, arranged oppositely, margin entire, elliptic in shape, the shape of the base and apex is obtuse (Tab.2).The venation primary veins are straight in course, lateral veins are about 10-16 pairs per leaflet, mostly alternate, more prominent on abaxial surface.Inflorescence is racemose-Corymb (Tab.3), the pedicel is greenish in colour, the length of the fruits, in Senna species, it ranges from 8.0-27.0cm with S. sophera having the lowest length of about 8.0 cm while S. alata having the longest range of 8.0-27.0cm. in Chamaecrista genus the length ranges from 1.5-6.8cm with C. mimosoides having the lowest range of 1.5-3.5 cm and C. kirkii having the highest range of 3.2-6.8cm whereas in Cassia genus the range is between 42-80 cm long with C. siberiana having about 42-76 cm while C. fistula have a length of 80 cm long.
In summary, irrespective of the fact that some of the characters measured overlaps, which is still an indication of some relative closeness of these genera and their species, leaf anatomical characters have been shown previously (Saheed and Illoh, 2010) to be useful in the delimitation of these same genera and species.The current work like the previous leaf anatomical studies (Saheed and Illoh, 2010) also justifies the separation of Senna and Chamaecrista from their initial Cassia genus thereby supporting the work of Irwin and Barneby (1981).To delimit these genera, morphological characters that were found to be useful in this study includes habit, leaflet apex and base, presence and absence of stipule, hairiness of sepals and the types of inflorescence, while those characters that could be employed in separating species include leaflet shape, apex, number in pairs, length and width as well as the length of the fruit.