Monday, 2 September 2013

Taxon of the Day: Drosera sect. Ergaleium

A Rainbow sundew - Drosera menziesii 

Today's Taxon of the Day entry has been written by Alastair Culham and his MSc Plant Diversity student Thomas Cooper.

In 1978 Rica Erikson coined the name ‘Rainbow sundews’ to describe a fascinating and unique group of climbing sundews from Western Australia that can grow up to 3 metres in length. These sundews, known botanically as Drosera subgenus Ergaleium DC. section Ergaleium, often climb over and through the sparse shrubs of Western Australia and can produce rainbow like effects as their sticky tentacles intercept sunlight. Unlike northern hemisphere sundews, which tend to occupy wet and boggy areas and are dormant in the cold winters, the Rainbow sundews have the ability to form an underground tuber for summer dormancy when their habitats dry out. There are currently 27 recognised species of Rainbow sundews, most of which occur in south-west Australia however a few spread out as far as the Himalayas (and possibly Africa). Drosera subgenus Ergaleium DC. section Ergaleium species are easily identified by their elongated and wiry stems (see picture below).

Drosera are one of three genera in the Droseraceae, which also includes Dionaea (Venus Flytrap) and Aldrovanda (Waterwheel Plant). The family is widespread, and has colonised a range of habitats. Aldrovanda is floating aquatic, with a widespread but infrequent distribution. Dionaea is restricted to the Green Swamp of North and South Carolina but has naturalised in Florida and in one small part of the New Forest (Hampshire, UK).

Drosera is the 2nd largest genus of carnivorous plants, comprising c. 200 species with a worldwide distribution of all continents except Antarctica. The mediterranean-type climate of South West Australia is thought to be a key factor in the major radiation of Drosera, with the adaption of tubers in the subgenus Ergaleium, long stout roots of the section Phycopsis, and tight reflective stipular buds of Drosera section Bryastrum helping the plants to survive the summer droughts and hot weather.

CoL Annual Checklist: Drosera
CoL contributor: Droseraceae Database
Image copyright: Alastair Culham

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