Adaptive radiation of bee-pollinated Gladiolus species (Iridaceae) in southern Africa

Observations on the flowers of 45 of 166 species of southern African Gladio lus (in sects. Blandly Densiflorus, Hebea, Heterocolon, Homoglossum, Linear ifolius, Ophiolyza) show that 42 species are pollinated largely by polylect ic bees in the family Apidae, 2 species by bees of the families Andrenidae or Halictidae, and 1 by a combination of hopliine beetles (Scarabaeidae) an d Andrenidae. The floral phenology attractants, diversity of floral forager s, and sometimes the rewards, vary according to geography and are not corre lated with taxonomy. Flowering in most Gladiolus species in the southern Af rican winter-rainfall zone coincides with the end of the wet season, August to October, but a few flower from February to April at the end of the dry season. They have sweetly fragrant flowers with a wide range of colors and markings. These species receive a diversity of floral foragers including be es in the genera Allodape, Amegilla, Andrena, Anthophora, Apis, and Pachyme lus. Most Gladiolus species of the summer-rainfall zone flower from Decembe r to April, from the middle to the end of the wet season, but a few species bloom from August to November, at the end of the dry season. Their flowers have no discernible fragrance and are colored mostly in shades of pink to mauve or white. Most floral foragers collected on these species were bees i n the genus Amegilla, but other bee genera, as well as flies in the genera Prosoeca and Stenobasipteron, were captured. Among the southern African spe cies of Gladiolus pollinated by bees, there are two distinct pollination st rategies. The majority have bilabiate, "gullet" flowers or "flag" flowers t hat secrete sucrose-rich nectar at the base of an obliquely funnel-shaped f loral tube 9-20 mm long with the loner, narrow part 5-15 mm long. Apis mell ifera and large-bodied anthophorine bees (especially Amegilla and Anthophor a) contact dehiscent anthers and/or receptive stigmas while probing the tub e for nectar with elongated probosces. In contrast, G. brevitubus, G. quadr angularis, and G. stellatus have rotate, actinomorphic (or subactinomorphic ) perianths offering little or no nectar at the base of tubes less than 7 m m long. Andrena species or Apis mellifera contact both dehiscent anthers an d receptive stigmas of G. stellatus or G. quadrangularis, respectively, whi le foraging for pollen. An additional 53 Gladiolus species also have bilabiate, gullet or flag flow ers with obliquely funnel-shaped tubes 9-20 mm long (the most common flower type in the genus), and are presumed also to be adopted for pollination by long-tongued anthophorine and honey bees. The actinomorphic, rotate floral form is present in 2 more species. Thus, 60% of the Gladiolus species in s outhern Africa may be regarded as being pollinated by Lees, and the overwhe lming majority of these species (95%) have gullet or flag flowers and are v isited primarily by long-tongued anthophorine bees that are foraging for ne ctar. The remaining species of Gladiolus in southern Africa have flowers wi th elongate perianth tubes and are adapted for pollination by sunbirds or i nsects other than bees, most importantly long-tongued flies (Nemestrinidae, Tabanidae), moths, and the large satyrid butterfly, Aeropetes.