thumb|Diphasiastrum complanatum

Diphasiastrum is a genus of clubmosses in the plant family Lycopodiaceae. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is placed in the subfamily Lycopodioideae. The genus was first proposed by Josef Holub in 1975, who characterized the species by their dorsiventral structure of branchlets, their chromosome number, and their special type of prothallium. Some species superficially resemble diminutive gymnosperms and have been given common names such as ground-pine or ground-cedar.

Features which Holub found to be distinct in most Diphasiastrum species inclulde distinct differences between dorsal and ventral surfaces of leaves, leaves arranged in 3 parallel planes (dorsal, lateral and ventral), leaves coming in 2 or 3 distinct forms, leaves arranged opposite and decussate on the stem, pairs of lateral leaves alternating with pairs consisting of one dorsal and one ventral leaf, complex prothallia, and typically 23 basal chromosomes. Diphasium, in turn, derives its name from "di-" meaning "two," and "phasis," meaning "appearance" or "phase," referring to the leaf arrangement in two parallel (dorsal and ventral) planes.

Species

, the Checklist of Ferns and Lycophytes of the World recognized the following species:

  • Holub, J. 1975. Diphasiastrum, a new genus in Lycopodiaceae. Preslia 14: 97-100.
  • Flora of North America - Diphasiastrum
  • Photo of D. complanatum
  • Picture and information
  • Pictures