Adaptive radiation of pollination mechanisms in Sparaxis (Iridaceae: Ixioideae)

Sparaxis metelerkampiae, which has dark purple flowers with an elongate perianth tube, belongs to a local guild of species with similarly colored flowers pollinated by the long-proboscid fly Prosoeca peringueyi (Nemestrinidae). Sparaxis parviflora, with tiny, bilabiate, scented flowers, has exposed anthers and is pollinated by native honey bees foraging for pollen and nectar. The remaining species have actinomorphic perianths and narrow floral tubes that contain trace amounts of nectar.

These are generalist species and they are visited by a broader range of insects, including hopliine scarab beetles, short-proboscid tabanid flies and, in some cases (S. bulbifera and S. fragrans) pollen-collecting bees. Outgroup comparison suggests that anthophorine bee pollination with nectar as the reward is ancestral in Sparaxis. Long-proboscid fly pollination has evolved at least once in the genus and a progression to increasingly symmetrical flowers in one clade has led from a generalist system using a variety of bee species in different families, hopliine beetles, and tabanid flies to a specialized system using only tabanid flies and hopliine beetles.