Physcomitrella patens has, like most mosses, a much simpler morphology then vascular plants, therefore this is an excellent model for studying developmental & physiological processes. It ’s genome is a great asset in comparative genomics as it can be used as an outgroup for the Angiosperms.

Further reading:

Rensing, S.A. et al. The Physcomitrella genome reveals evolutionary insights into the conquest of land by plants. Science 319, 64-9 (2008). [pubmed]