langii Fanning et al. (1990)[1] Caia is a genus of small fossil plants of Late Silurian age (around 430 to 420 million years ago).

The diagnostic characters are naked parallel-sided axes branching isotomously, terminating in vertically elongate sporangia (spore-forming organs) which bear spinous emergences particularly at the distal ends.

[1] The only known species is from Hereford, England.

Cladistic analysis suggests that the genus may belong to the Horneophytopsida, a class of the polysporangiophytes, as it lacks vascular tissue and has branched stems bearing sporangia.

This article related to a Silurian plant is a stub.