Plant of the Month — May 2006
Senna glutinosa (DC.) Randell
The Sennas belong to the Caesalpiniaceae family and have flowers of deep, rich yellow that make a vibrant contrast against the red soil on which many of them grow. Senna glutinosa is found on a variety of soils, including sand dunes. It is not found on the Swan Coastal Plain, but favours mainly the soils from Kalgoorlie north to Broome and east to the Western Australian border and beyond. There are two southerly populations north and north-west of Esperance.
Growing from 0.3m-4m high it can be a shrub or small tree, depending on its environment. The leaves of Senna glutinosa have been described as having a metallic lustre rather than being shiny and its twigs described as ‘sticky’. Its species name, ‘glutinosa’, from the Latin gluten -inis (glue) and osus (abounding in), refers to this character. Generally, stickiness in plants acts as a protection against heat by reflecting light, especially if that stickiness hardens. As this plant’s environment includes some of the hottest temperatures in Western Australia this may be one of the methods by which it protects itself against the searing heat.
While Senna glutinosa is absent from the Swan Coastal Plain, the genus Senna has many species that bloom for long periods with flowers of a deep butter yellow to gold which would add light and contrast to any surroundings. Ask at your local nursery for this species and if not available, for the next best; they should have at least one. Otherwise, travellers north may enjoy its gold between March and December.
Photo: T. Tapper
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