Diosma demissa – a species threatened!

Diosma demissa is a rare fynbos member of the Rutaceae (citrus) family that has a very interesting distribution. It grows only on coastal limestone ridges with two populations; one on the coast near Gansbaai and the second some 90km away across the South Atlantic on a short section of coastline in the Cape Point Nature Reserve.  This disjunct distribution, surely the consequence of shifting sea levels that has seperated a once continuous coastal population over time?

Diosma demissa growing on limestone at Gansbaai Diosma demissa has aromatic, lance shaped leaves that are alternately arranged on the stem. It is able to resprout after fire from a woody caudex and produces 2 to 3 flowers in clusters at the end of its stems from March to June. Diosma demissa - limestone fynbos Gansbaai

Unfortunately the main population of this species at Gansbaai is being severely impacted by the rapid development of the town as well as dense infestations of the invasive species, Acacia cyclops. These were planted along this section of coastline in the 1950’s to stabilise coastal dunes.  It is estimated that as much as 50% of the remaining natural populations of this species will be lost to alien vegetation and urban development over the next decade. Another example of a lowland fynbos species under severe threat!

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