It has narrow clover-like leaves, and cream-coloured, frilly flowers with a yellowish centre, looking a bit like a small butterfly or a set of elk antlers.

[1] The American botanist Thomas Nuttall was the first to describe large clammyweed in 1834, which he placed in a new genus and named Cristatella erosa.

In 1842, Stephan Endlicher, an Austrian botanist who was the director of the Vienna Botanical Garden moved the species to a new genus and renamed it to Cyrbasium erosum, which is an illegitimate name.

In 1958 Hugh Iltis concluded the species could better be assigned to the genus Polanisia, a name that has priority over Cristatella, since it was already erected by Constantine Samuel Rafinesque in 1819, and made the new combination P. erosa.

Each capsule contains twelve to forty, globular to ovate, dark reddish brown seeds of 1½–1¾ mm (0.06–0.07 in), with a nobbly surface.

[2] Large clammyweed naturally occurs in Texas and adjacent parts of Arkansas, Louisiana and Oklahoma, where it can be found in fields, prairies, sandy hillsides and open woodland.