Family Amaranthaceae > Subfamily Gomphrenoideae.
Plants of the World Online (Kew) accepts 34 species with other sources ranging from 20 to 45.
Almost all are from the tropical areas of N. and S. America.

Most are annual or perennial herbs, sub-shrubs, shrubs or vines.
Stems can be prostrate, prostrate with erect tips, trailing or climbing by scrambling.
Branches are opposite and stems are flattened at the nodes.
Stems may have no hairs (trichomes) up to dense simple or branched ones .

The opposite to sub-opposite leaves are on a petiole.
The ovate, elliptic, oblong or lance-shaped blade has a smooth or finely toothed edge.
The lower surface may have no hairs or dense straight or crooked, simple or branched ones.

Inflorescences are terminal on the main stems and the branches.
Many are panicles that branch up to 4 times with the branches being in whorls, opposite or alternate.
The small flowers along each branch or spike are, or almost, directly attached with no pedicel.
At each branch is a bract and the flowers have 2 bracteoles under them.
The membranous bracts persist on the fruit.

The unisexual flowers have 5 free or basally fused tepals.
They often have tufts of hairs on the outer surface.
Female flowers have a ring of long hairs around their base between the sepals and bracteoles.

Male flowers have 5 (1 to 5) fertile stamens with anthers opening inwards.
The filament bases are shortly fused and there may be infertile staminodes between them.
There may be a rudimentary ovary.
Female flowers have a superior ovary with 1 pendulous ovule.
There is a very short (0.2 mm) or no style and 2 or 3 mostly linear stigma lobes.

The membranous compressed spherical capsules (utricles) have 1 dark red-brown seed.