Radiation of Pollination Systems in the Cape GenusTritoniopsis(Iridaceae: Crocoideae) and the Development of Bimodal Pollination Strategies

Abstract

Floral morphology and observations on insect and avian visitors to species of the southern African and largely Western Cape genus Tritoniopsis indicate that short‐tubed pink flowers, ancestral in the genus, are pollinated by anthophorine bees forging for nectar. Multiple shifts to more specialized pollination systems have occurred in the genus during its evolution. Four species with elongate floral tubes and a pink to red bilabiate perianth are pollinated either by sunbirds (Nectarinia) alone or by sunbirds and the satyrid butterfly Aeropetes tulbaghia. Another red‐flowered species with an actinomorphic flower is inferred to be pollinated only by Aeropetes, while two species with pale pink flowers with red markings are pollinated by long‐proboscid flies in the genus Prosoeca (Nemestrinidae). Tritoniopsis parviflora is unique in the African Iridaceae in producing floral oils as a reward to the short‐tongued bee Rediviva gigas (Melittidae), as well as conventional sugar nectar. Tritoniopsis nervosa has white, sweetly scented, long‐tubed flowers and is assumed to be pollinated by night‐flying moths. Although relationships within Tritoniopsis are poorly understood, it is clear that at least five shifts in pollination strategy have occurred in this genus of just 24 species. Studies also show that bimodal pollination systems using two different pollinator groups occur in several species, using sunbirds and Aeropetes, anthophorine bees and nemestrinid flies, or oil‐collecting Rediviva and nectarivorous bees. Such bimodal systems are probably important for the successful reproduction of these plants.