This was originally noticed during landcare projects during the late 1980s and 1990s, growing near or even in water. A. derwentiana superficially resembles the species A.axillaris and A. riceana, and was originally thought to be a variant form of one of these other two species. Tasmanian Herbarium botanist Alan Gray classified it as a new species after some years work, bringing the number of known Tasmanian endemics to four.
Although the three species mentioned are apparently closely related, each can be differentiated by a combination of reproductive and vegetative characteristics. The new species is possibly vulnerable due to ongoing degradation of its riparian habitat.
A small to medium shrub 1-3 metres high, usually multi-branched from the base or with a short trunk, the branches semi-spreading to sub-erect, becoming very slender, arching and pendulous towards their extremities. New growth soft and often bronze to reddish in colour, whereas older smaller branches are finely grooved, greyish to brown with fine hairs. The canopy is dark green and dense lower down, but more open in the upper parts. The phyllodes are alternate, separately more widely on the slender terminal branches, but rather more crowded on the lower branches and on shorter axillary branches.
||The flower head is a loose cylindrical
spike, approximately 25 mm long on a peduncle (short stem) 5-8 mm long,
single or, more usually, paired in the axils of the upper phyllodes; there
are usually 5-8 flowers per spike, coloured pale yellow to almost lemon
The seed pod is dark brown, approximately 25-35 mm long and 2-4 mm wide with dark brown, lustrous seeds.
Flowering period: Oct. - Dec .