Many of the 100 species are from South America with some from Malaysia.
Australia has 18 native species.

They are annual or perennial herbs to 35 cm high or subshrubs up to 1.5 m.
Stems can be erect, prostrate or prostrate with erect tips.
Stems may have vertical grooves and be thickened at the nodes.
They branch the whole way up.
Young stems and branches have soft white hairs that lie flat along the surface.
Hairs are often dense, woolly and tangled.

The opposite leaves have no petiole or one up to 1 cm long.
Blades are 2 to 6.5 cm long and up to around 1.5 cm wide.
They can be ovate, obovate, elliptic to oblong or lance-shaped.
The edges are smooth, the tip pointed and the base may run down the petiole.
The upper surface may have no, or a few hairs and the lower surface is usually sparsely to densely hairy.
The long white hairs can be simple or branched (dendritic).

Inflorescences are almost all terminal with occasional axillary ones.
Directly attached to the hairy receptacle (top of the stem) they are almost spherical heads or spikes.
Heads are around 1.25 cm across and the oblong spikes are 2 to 4 cm long and up to around 1 cm wide.
The 2 leaves (involucral bracts) below the head have no petiole.

Flowers, around 5 mm long have 1 triangular bract and 2 bracteoles.
The bracteoles fold around the flower with each covering one side.

Flowers have 5 often unequal tepals around 5 mm long in 2 whorls.
Oblong or lance-shaped with a mucro at the tip their bases are free or fused for a short distance.
The outer 3 are flattish with dense woolly hairs at the base of the outer surface.
The inner 2, with a thickened base have woolly hairs all over the outer surface except the tip.
Tepals can be colourless, white or brightly coloured.

The 5 stamen filaments are fused into a tube with 5 bilobed teeth on the rim.
The anthers are attached to the top of the tube between the teeth.
The superior ovary has 1 locule with one pendulous ovule.
The 1 to 4 mm long style has 2 linear stigmas.

The fruit is a compressed obovoid, oblong or ovoid capsule known as a utricle.
They rupture irregularly or not at all.
The shiny brown compressed round to ovoid seed is around 1.5 mm across.