EVOLUTION AND HOMOLOGY OF BIRD POLLINATION SYNDROMES IN ERYTHRINA (LEGUMINOSAE)

Erythrina L. (Leguminosae: Phaseoleae) is a pantropical genus of over 100 species, all of which are either hummingbird or passerine pollinat ed. Phylogenetic hypotheses based on morphological and chloroplast DNA restriction site characters suggest that shifts from passerine to hum mingbird pollination have occurred a minimum of four times in the genu s. In hummingbird-pollinated species the inflorescences are held uprig ht, the flowers are arranged radially along the axis, and the narrow s tandard petal is conduplicately folded to form a pseudotube. In most o f the passerine-pollinated species, the inflorescences are held horizo ntally, the flowers are secund, and the standard petal is open so that the nectar and androecium are easily visible and accessible. Nectar a mino acid concentrations and sucrose to hexose ratios are closely asso ciated with pollination mode. Despite the general resemblance in flowe r and inflorescence morphology among species with the same pollination type, homology assessment reveals that petal morphology and size, and calyx and pollen morphology differ. Morphological characters, even if comprising modifications associated with adaptive pollination systems , therefore provide useful phylogenetic information.