Rattlepods are in Family Fabaceae > Subfamily Faboideae > Tribe Crotalarieae.
There are 600 to 700 species with over half from Africa.
S. E. Queensland has around 19 of the up to around 40 species in Australia.
Some were grown as ornamentals but these days they are mostly seen on waste ground where they are a minor weed.
Most are erect annual or perennial herbs from 40 cm to 1 or 2 m high.
There are some shrubs to 5 m and a few are prostrate.
There may be hairs on the stems, leaves and inflorescences.
Leaves are on a petiole and stipules may be absent, minute or up to 2.5 cm long.
Free of the petiole they can be leafy, linear to broadly ovate and persist or fall off.
The alternate leaves can be simple but most have 3, 5 or 7 leaflets.
Leaflets can be linear to broadly ovate, obovate or elliptic.
Lateral leaflets may be more or less than half the length of the longer terminal one.
There may be hairs on the lower or both surfaces and some species have glands.
Inflorescences are mostly terminal with some leaf-opposed and a few axillary.
They are occasionally a solitary flower but most are a raceme.
Racemes have flowers, on a pedicel along a central midrib or rachis with the lower flowers opening first.
Racemes are up to around 30 cm long and the flowers up to 5.5 cm.
Bracts are usually present and sometimes bracteoles.
Flowers can be spread out or densely arranged.
The 5 sepals can be free or have their bases fused.
Occasionally the calyx has 2-lips with 2 lobes in the upper and 3 in the lower.
Hairs may be present or absent.
The 5 petals form a typical pea-shaped corolla.
The upper ovate, oblong or roughly circular standard petal can have a pointed or rounded tip.
The 2 smaller wing petals on the sides can be shorter or longer than the keel petals.
The 2 lower keel petal are partially fused along their lower surface.
All may have short hairs mainly on the claw bases.
Petals are greenish-yellow, pure yellow or yellow with pale or dark red, brown or purplish veins.
Stamen filaments may all be free but typically their bases are variously fused into a tube that is open on the upper side.
The free portion of the filaments carry alternating long basifixed anthers and short dorsifixed ones.
The superior ovary has 1 locule, a curved style with hairs near the tip and a small stigma.
Fruit pods, up to 4.5 cm long may be smooth or hairy.
The beak, from the retained style may be long or short.
The kidney-shaped seeds become loose and rattle in the pod.