Pollination of Moraea species (Iridaceae) with a staminal column

The ancestral and most common flower in the African genus Moraea is Iris-li ke and consists of three functional units (meranthia). Each unit consists o f an outer tepal opposed to a broad style branch terminating in prominent p aired crests, together forming a gullet-like unit. However, many species in this genus of some 200 species have mechanically protandrous flowers in wh ich the three stamens form a sheath surrounding the style and the style bra nches are narrow, with reduced stigmatic crests, and the subequal inner and outer tepal whorls form a shallow or deep howl sometimes fully enclosing t he stamens and style branches. The flowers secrete hexose-dominant nectar a nd, except for M. collina, are self-incompatible. Flowers of the nine speci es in two sections studied comprise two different modes of pollination base d on the presentation of the staminal column and perianth, pigmentation, sc ent, and edible rewards. In five species, M. collina, M. comptonii, M. eleg ans, M. ochroleuca, and IM. vallisbelli, the perianth forms a wide or narro w howl and produces strong, sweet or musk-like odors, and the weakly diverg ing anthers are appressed to the narrow, inconspicuous style branches. Thes e flowers are pollinated primarily by flower flies, scarab beetles, and hon ey bees that land on the perianth and brush against the anthers and/or rece ptive stigmas while foraging for nectar or pollen, or in the case or beetle s merely assembling on the flowers. In the second group of species, M. bifi da, M. miniata, M. pseudospicata, and M. reflexa, the perianth is stellate, pink, yellow, or blue, usually without discernable scent, the filaments ar e united into a column that is exserted from the flower, and the anthers ar e usually coherent. These flowers are pollinated primarily by polylectic be es in the families Apidae (Anthophora diversipes, Apis mellifera) and Melit tidae (Rediviva spp.). The bees land on the staminal column and forage for pollen, sometimes later moving onto the perianth to take nectar present at the base of the tepals. The columns of these species are interpreted as bot h morphological and functional intermediates between pollen presenters or p rotostigmas (e.g., in Asterales, Campanulales, Proteales) and true gynostem ia/gynostegia (in Asclepiadaceae, Orchidaceae, and Stylidiaceae). These flo wers represent a profound shift in the ancestral pollination strategy in th e genus from one of passive pollen deposition on bees foraging for nectar o n meranthia to one of active foraging for nectar or pollen on whole flowers .