Abstract
Anatomical characters often provide strong taxonomic evidence and many times help define species whose morphological limits are in question. This study aimed to survey characters of the leaf anatomy of 16 species of Crotalaria L. occurring mostly in the cerrado (savanna) of central Brazil and in areas of restinga (coastal woodland, or sandy forest) along the coast of the country, in order to improve the current taxonomic circumscription of sections and species. Leaf samples were collected in the field and obtained from herbarium specimens. Standard techniques in plant anatomy were employed, including analyses under light and scanning electron microscopy. Many of the characters analyzed are relatively uniform, but some are diagnostic for species. At the section level, only trichomes with a base composed of radially distributed cells proved useful in the diagnosis of C. sect. Calycinae. The other characters analyzed showed interspecific variation, but no diagnostic value for recognition of the sections. At the species level, unlike the results found for sections, various characters have diagnostic value. Among the characters with diagnostic value at the species level, those related to texture, the venation pattern (such as the formation of areolas and insertion of the ribs secondary to midrib), and, in particular, the epidermis, showed potential for aiding the circumscription of some species.
Highlights
Crotalaria L. (Leguminosae: Papilionoideae) is the only genus of the tribe Crotalarieae with native representatives in South America (Wyk 1991; Wyk & Schutte 1995)
We sampled leaves from a total of 48 specimens, belonging to 16 species of Crotalaria, occurring in open habitats: most are from the cerrado and campo rupestre formations, both in the Cerrado Biome in central Brazil, two specimens were collected from the sandy restingas of the southeastern Atlantic coast of Brazil
The primary venation pattern in all of the studied species of Crotalaria is pinnate, whereas the secondary venation pattern is brochidodromous and characterized by secondary veins that do not terminate at the margin but join to form arches (Fig. 1A-P)
Summary
Crotalaria L. (Leguminosae: Papilionoideae) is the only genus of the tribe Crotalarieae with native representatives in South America (Wyk 1991; Wyk & Schutte 1995). The genus is one of the largest in the family Leguminosae (Lewis et al 2005) and comprises some 720 species distributed mainly in tropical and subtropical areas of the southern hemisphere (Wyk 2005) with the principal center of diversity in the central-south and eastern regions of Tropical Africa (Polhill 1982). The most widely accepted infrageneric classification of the group is that proposed by Bisby & Polhill (1973), which is based mainly on the morphological characters of the flowers of African species. Roux et al (2013) proposed a new infrageneric classification for the entire genus, based on molecular and morphological evidence, resulting in 11 recognized sections. The plants of Crotalaria can be recognized by the presence of simple leaves or leaves containing one to three leaflets, a rostrate keel, a style with trichomes in a single or double line toward the stigma, a monadelphous androecium (5 + 5-anther configuration), paired callosities on the standard petal and highly inflated fruit (Polhill 1982; Wyk 2005)
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