A shrub to 3 metres tall by 2 metres wide. It is a species which is variably complicated in terms of taxonomy and morphology.
There are about 11 subspecies of this plant (8 currently in NSW) and they inhabit the dry inland areas of all mainland Australian states. Overall, the species occurs from as far east as the Singleton-Morisset area in NSW, spreading west through virtually all parts of NSW, into all surrounding states; South Australia and Northern Territory as well as Western Australia and Queensland. It does not occur in Tasmania naturally.
It is found in dry sclerophyll woodland, mallee shrublands and mulga-scrub as well as desert shrublands. They can also be found colonising cleared roadsides.
Senna spp. tend to have alternate and compound leaves (paripinnate with even numbers of leaflets in pairs), sometimes with a gland on the petiole; or foliage produced as phyllodes. In this species, they are highly variable, with up to 5 pairs of leaflets per leaf, overall to 6 cm long and up to 4 cm wide, with leaflets ranging from terete (tubular) to linear and narrow, to elliptic / broad-elliptic depending on the particular subspecies; hairy to glabrous; green to blue-green or blue-grey.
Senna spp. produce rotate 5-petaled yellow to green flowers (sometimes – the petals are of unequal size), very bright and conspicuous in raceme-like clusters in leaf axils. Senna artemisioides produces bright yellow flowers up to 2 cm in diameter which are borne in small clusters in the leaf axils; produced over a long period from late Autumn/early Winter through to Spring. Plants can be very showy in full flower.
Senna spp. produce a pod (being in the Fabaceae family). These are brown/black, 4-8cm long x 1 cm wide.
Once established, this species needs no additional watering and the only maintenance is to lightly prune after flowering to maintain shape as they tend to become straggly with age.
The subspecies I have grows to approximately 1.5 metres high and about the same width. It is hardy, long lived and long flowering. It has the additional bonus of being a legume – which means it improves soil fertility through ‘fixing’ nitrogen.
When I became interested in Australian native plants in 1976, this was the first plant I grew in my garden in the northern Sydney suburb of Westleigh. After joining the Australian Plants Society, I obtained seeds from their seed bank and successfully germinated them after treatment with boiling water.
Editor’s notes: this species is a very attractive plant to grow. Best results are obtained in full sun with a fast-draining sandy soil. The subspecies with glaucous foliage are very attractive, especially when this foliage contrasts with copious bright yellow flowers. It may struggle in cold climates but worth a try.
Treat seed in boiling water prior to sowing.
The subspecies of this species are referred to as ‘nothosubspecies’ which means they have arisen as hybrids between other subspecies. Further taxonomic work is required to sort out this species complex. The current subpecies in NSW are:
Whichever subspecies you choose to grow, they are all attractive.
Senna plants regenerate from seed after fire and can likely reshoot from basal parts / suckering.
Senna is a large world-wide genus of about 350 species. Australia has about 46 species – all of which are endemic. NSW has about 20 species. There are also have some weed species which can be prolific in coastal areas. A lot of these native Senna spp. used to be known as Cassia spp. (and sometimes ‘cassia’ is part of the common name).
Senna – reportedly derived from the Arabic sana – a name applied to plants which have laxative properties.
artemisioides – Latin – resembling the genus Artemisia – a genus of daisies – which occur mostly in the northern hemisphere.
This species is not known to be at risk of extinction in the wild (very common).
NSW Flora Online (PlantNET) – Senna artemisioides group profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Senna~artemisioides+group
Australian Native Plants Society Australia – Senna artemisioides profile page https://anpsa.org.au/plant_profiles/senna-artemisioides
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Mallee Design – Happy Yellows – Senna artemisioides profile page https://malleedesign.com.au/happy-yellows-senna-artemisioides/