Family Fabaceae > Subfamily Faboideae > Tribe Desmodieae.
The genus has been frequently redefined and will probably change again.
Plants of the World Online currently accepts 179 species, others up to 200.

Most of the 30 native species formerly listed in Australia have been moved to other genera leaving 3 naturalised species.
Most are herbs with a few small shrubs.
Stems may have a spine at the tip and commonly have curved and hooked hairs.
Hairs can be sparse or so dense the stems look white.

Alternately arranged leaves are on petioles with stipules, up to 1.5 cm long at the base.
Leaflets, up to around 10 cm long and 4.5 cm wide are on petiolules a few mms long.
There are stipels beside the leaflet petiolules.

Leaflets can be ovate, obovate, lance-shaped, oblong, oblanceolate and occasionally diamond-shaped.
The tips can be pointed to widely rounded.
Leaflets can have sparse to dense hairs on both surfaces or just the lower.
On the lower surface they can be all over the surface or just along the veins.
Hairs are long curved ones that lie along the surface and tiny hooked ones.

Terminal and/or axillary inflorescences are mostly racemes with some in clusters.
Racemes have flowers, on pedicels along a midrib with the lower ones opening first.
There can be a few up to 100 flowers and bracts are present.

The flowers, around 5 to 10 mm long are typical pea-like ones with 5 petals.
The short calyx tube has 5 sepal lobes or 4 when the upper 2 are fused.
The upper and largest standard petal is roughly circular.
The side wing petals are often joined to the centre of the keel petals.
The 2 keel petals, fused along the lower edges are folded up.
Petals are pink, purple or blue.

Some or all of the stamen filament bases may be fused into a tube and the anthers are all the same size.
The elongated ovary, sometimes on a stalk has a curved style.
The fruit are loments – a pod with each seed in a clearly defined segment.
Pods can be flat or swollen and have hooked hairs.