Pollination of seven Plectranthus spp. (Lamiaceae) in southern Natal, South Africa

The genus Plectranthus (Lamiaceae) shows remarkable radiation on the sandst ones of southern Natal and northern Transkei in South Africa, where six end emic species occur. Two of these endemic species, P. hilliardiae and P. ori biensis, are included in this study, as well as P. reflexus, for which only limited data are available. The other species that were studied are P. amb iguus, P. ciliatus, P. ecklonii, P. madagascariensis and P. zuluensis; Four of these taxa, P. ambiguus, P. hilliardiae, P. reflexus and P. saccatus va r. longitubus, have uniquely long corolla-tubes (20-30 mm) and this is rela ted to pollination by nemestrinid flies of the genus Stenobasipteron that h ave proboscides of similar length. Other nemestrinid species of the genus P rosoeca have shorter proboscides and pollinate two species of Plectranthus with shorter corolla-tube lengths (6-15mm). Acrocerid flies, tabanid flies and anthophorid bees are also important visitors to these species. This stu dy on the pollination of seven species of varying corolla-tube lengths show s a correlation between floral tube length and proboscis length of insect v isitors, many of which are recorded for the first time as pollinators of Pl ectranthus.