A review for the pollinators of Papilionaceous flowers

Abstract

The evolution of keel flowers within Fabaceae, Polygalaceae and some other clades of angiosperms is attributed to skilled and strong bees. However, whether this is true or not, is still an open question. Therefore, the literature is surveyed for the Hymenopteran pollinators of keel flowers, for 119 sources and for 112 species, six genera and two tribes for five characters which are the size of the flowers, Hymenopteran flower visitors/pollinators, size of the Hymenopteran pollinators, pollen and nectar robbers/thieves and size of the Hymenopteran thieves/robbers. The results suggest that Fabales keel flowers are mainly pollinated by long-tongued bees, from Apidae and Megachilidae families; and the most common pollinators of the keel flowers are small Megachile and Osmia; medium-sized Apis, Anthophora and Eucera; and large Xylocopa, Bombus and Centris. While the literature suggests that keel flowers are pollinated by skilled and strong bees, the results of the current review have shown that this is not the whole case in terms of flower size and bee size. There is no difference between pollinator diversity and flower size. While floral robbers/thieves are mostly up to 2 cm, among them honey-bees (Apis mellifera) both pollinate and rob the keel flowers. Keel flowers of Polygalaceae and other angiosperm lineages are somehow similar to the keel flowers of Papilionoideae.