Abstract
D.Phil.
The genus Crotalaria (tribe Crotalarieae, Fabaceae) includes 700 species with its
main centre of species diversity in Africa and Madagascar and secondary radiations to
other parts of the world (including North and South America, India, South-East Asia and
Australia). Molecular systematics has recently provided profound new insights into
generic relationships in the Crotalarieae, thereby creating the opportunity to re-evaluate
the taxonomic and functional significance of flower and fruit structure in the tribe, with
emphasis on the large genus Crotalaria.
A representative sample of flowers from 211 species was dissected to record
morphological character states and fruit transverse sections of 142 species was cut to
record anatomical variation across the tribe. These data were supplemented from the
literature to allow for generalizations.
Six structural-functional flower types were identified: (1) pump; (2) gullet; (3)
hugging; (4) saddle; (5) tunnel; and (6) brush. The saddle and tunnel types are here
described for the first time. Crotalaria is the only genus within the tribe that has the
brush type; specialized flowers characterized by a rostrate keel, highly dimorphic
anthers, stylar trichomes and four types of elaborate callosities on the standard petal:
(1) ridge callosities – vertical swellings on the blade and claw; (2) disc callosities – subcircular
swellings on the blade; (3) columnar callosities – cylindrical protruding
appendages on the blade; and (4) lamelliform callosities – plate-like protruding
appendages on the blade. Trends toward specialization are apparent across the
phylogeny as a whole suite of specialized floral characters and are homoplastic as a
result of convergence.