The long-proboscid fly pollination system in Gladiolus (Iridaceae: Ixoideae)

Pollination strategies of Gladiolus, one of the largest genera of the monocot family Iridaceae, are unusually diverse and involve various bee species, foraging either for nectar or for pollen, or moths, a large butterfly, passerine birds, and long-proboscid flies foraging for nectar. The latter system has been demonstrated for 16 species of Gladiolus of diverse taxonomic affinities. These species are primarily or exclusively pollinated by flies with elongate mouthparts. All have similar flowers with a slender, elongate perianth tube, mostly 25-50 mm long, a white to cream or pink perianth, usually marked with pink or red nectar guides on the lower tepals, and lack floral odor. The flowers produce ample quantities of sucrose-rich to sucrose-dominant nectar of moderate sugar concentration. Each of these species is pollinated by one or two species of flies of the families Tabanidae or Nemestrinidae, which have mouthparts usually 20-60 mm long, exceptionally to 80 mm in Moegistorhynchus longirostris. An important aspect of long-proboscid fly-pollination systems is the formation of guilds in which a number of species of plants of different genera and families have similar flowers and utilize the same pollinator. In these guilds pollen placement on the pollinator’s body is fairly precise, and different members of a guild at any site use different parts of the pollinator’s body for pollen transport. An additional 13 species of southern African Gladiolus have flowers conforming to those pollinated by long-proboscid flies and are thus inferred to have this pollination strategy. These species extend from the southern African winter-rainfall zone in the southwest to the Drakensberg Mountains of the eastern half of the subcontinent and flower at precisely the times that long-proboscid flies are on the wing, mostly late spring in the west (mid September to November) or late summer in the east (February to April). An autumn-flowering guild using a different fly species occurs in the southern part of the winter-rainfall zone. The taxonomic relationships of Gladiolus species pollinated by long-proboscid flies are diverse, with these 29 species falling in six of the seven sections of the genus occurring in southern Africa, and the pollination system appears to have evolved independently in each section.