What is Physcomitrella?
Green plants first expanded their habitat onto land by the early Silurian (430 million years ago), and subsequently diverged into various lineages with different morphologies. The bryophytes and the ancestor of vascular plans diverged early in land plant evolution. Mosses are bryophytes, and their morphologies and life cycles differ significantly from those of flowering plants, to the fascination of plant evolutionary biologists. Furthermore, many of their physiological and developmental traits are probably shared with flowering plants, such as regulation by phytohormones (e.g., auxin and cytokinin) and intracellular messengers (e.g., Ca2+). Therefore, Physcomitrella provides an opportunity to analyze the actions of these substances in a simple system.