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.
Highlights
The genus Pelargonium L’Hér. ex Aiton (Geraniaceae) includes approximately 280 species distributed amongst 16 sections (Bakker et al 2004)
Pelargonium dipetalum L’Hér. is the only member of this alliance occurring along the southern coast in Western Cape Province and extends from Betty’s Bay to Knysna
The hypanthium in P. dipetalum typically varies between 7 mm and 18 mm in length, but the species includes a few populations east of Swellendam with exceptionally long hypanthia, 35 mm – 50 mm long. These populations were not recognised as a separate taxonomic entity by Marais (1994), who made no correlation between their distribution and their distinctly longer hypanthium
Summary
The genus Pelargonium L’Hér. ex Aiton (Geraniaceae) includes approximately 280 species distributed amongst 16 sections (Bakker et al 2004). The hypanthium in P. dipetalum typically varies between 7 mm and 18 mm in length, but the species includes a few populations east of Swellendam with exceptionally long hypanthia, 35 mm – 50 mm long These populations were not recognised as a separate taxonomic entity by Marais (1994), who made no correlation between their distribution and their distinctly longer hypanthium. This variant was, identified by Manning and Goldblatt (2005) as representing a distinct morph adapted to pollination by the long-proboscid fly Prosoeca longipennis Loew (Nemestrinidae). 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
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