A new long-tubed subspecies of Pelargonium dipetalum (secton Hoarea) (Geraniaceae) from the Albertnia-Swellendam area in Western Cape Province, South Africa

Abstract

Background: Field studies confirmed that unusually long-tubed populations of Pelargonium dipetalum from between Swellendam and Albertinia, Western Cape Province, South Africa, are a distinct ecotype adapted to pollination by the long-proboscid fly, Prosoeca longipennis. The geographical and morphological isolation of these populations suggests that they are reproductively isolated from short-tubed populations, which are pollinated by bees. Objectives: To determine and describe the floral variation in P. dipetalum, with a view to recognising the long-tubed populations at some taxonomic level. Method: All available collections were measured and compared. Results: Populations of P. dipetalum were segregated into a short-tubed form with hypanthium 3 mm - 24 mm long and mostly pink petals that occurs from Betty's Bay to Knysna, and a long-tubed form with the hypanthium 34 mm - 54 mm long and consistently white petals that is restricted to a small area east of Swellendam between Suurbraak and Albertinia. We described the long-tubed form as the new subspecies P. dipetalum subsp. stenosiphon. Conclusion: The new subspecies increases our understanding of the diversity in P. dipetalum and represents a new taxon of conservation concern.