Sunday, August 5, 2012
Strophanthus and its spidery tresses, a useful plant
This shrub in the Princess of Wales Conservatory might not look much from a distance but up close the flowers are not only richly coloured yellow and red-brown but they have these very cool threadlike extensions to their petals.
All the species of Strophanthus have them but Strophanthus preisii, the one in flower in the Conservatory now, has the longest, up to a foot long. (For Australian readers, a foot is found at the end of a Roman living in the British Isles around 1 AD and was reputedly about 30 centimetres long.) I couldn't get far enough away to fit them in but here you can see a few more inches more in this picture.
Not all the flowers of Strophanthus are chocolaty banana in colour - some are quite cheery bright colours (e.g. Strophanthus gratus and Strophanthus speciosus with bright reds and yellows) - but most have petal tresses of some length.
Like most of its fellow strophanthians this one can be found in the tropical forests of Africa. And like lots of its siblings in the family Apocynaceae, it contains some toxic chemicals. In this case the sap is used to cure various ailments in humans as well as kill fish (although other species of Strophanthus are more poisonous): 'strophanthin' is a muscle-stimulant like digitalis. On the other hand, young leaves are cooked and eaten as a vegetable in Gabon.
Strophanthus preisii is sometimes called Poison Arrow Vine but Spider Tresses is to be preferred, in my mind. I must ask Henk Beentje, one of our Kew herbarium botanists and an expert on this genus (and many other African plants) what he thinks. I could also ask him how such long tresses might assist this species in pollination.
Henk published a taxonomic revision of Strophanthus back in 1982, with a reprise in the curiously titled The Useful Plants of West Tropical Africa. I've always had a mischievous desire to publish a book on the useless plants of the world; sadly Strophanthus preisii wouldn't feature.