Pollination biology of Lapeirousia subgenus Lapeirousia (Iridaceae) in southern Africa; floral divergence and adaptation for long-tongued fly pollination

Lapeirousia subg. Lapeirousia (Iridaceae) consists of 21 species endemic to sub-Saharan Africa, with the Mediterranean southwestern part of southern Africa the center of diversity. Analysis of the floral ecology of 19 species shows that the majority secrete large amount of sucrose-rich or sucrose-dominant nectar, and the 16 species for which pollinator observations were obtained are cross-pollinated exclusively by insects with elongated mouth parts representing three orders (Diptera, Hymenoptera, and Lepidoptera). In the absence of pollinators, at least four species (L. arenicola, L. jacquinii, L. oreogena, L. simulans) were found to set seed without cross pollination and are assumed to be mechanically autogamous. The 20 species segregate into three pollination types based on divergent patterns of pigmentation, scent production, perianth tube length, and pollinator taxa. Species with flowers of the L. silenoides-type are pollinated exclusively by Proseca species (Diptera: Nemestrinidae), and species with flowers of the L. fabricii-type are pollinated exclusively by Moegistorhynchus longirostris (Diptera: Nemestrinidae) and Philoliche gulosa (Diptera: Tabanidae). The latter two fly species, together with the Prosoeca species, have the longest mouth parts of all pollinators examined on species of subgenus Lapeirousia. The L. divaricata-type flower is pollinated by a combination of bees., mostly female Anthophoridae (e.g., Anthophora, Amegilla, Tetraloniella) and native Apis mellifera (Apidae), and to a lesser extent by bombyliid flies and some Lepidoptera. Observations of insect pollen load analysis suggest that the evolution of these three flower types has encouraged ethological isolation between species, but is a small component in broader pollination guilds encompassing co-blooming species in other genera and families, including Asteraceae, Geraniaceae, Scrophulariaceae, and Sterculiaceae. Mapping of pollination syndromes on a phylogenetic tree of subgenus Lapeirousia demonstrates the extreme adaptive radiation in the subgenus and the convergent development of the same pollination strategy repeatedly across the subgenus.