Figure 2. The life cycle of P. patens.

A haploid (n) spore germinates to form chloronemal cells. A chloronemal apical stem cell transitions into a caulonemal apical stem cell (shown by change in division angle), which forms filaments of caulonemal cells (1D). Side branch initials form that can give rise to either filaments (2D) or gametophores (3D). A characteristic oblique division distinguishes a filament initial from a gametophore initial. A regimented series of cell divisions leads to the formation of a gametophore with leaf-like phyllids arranged in a spiral phyllotaxy. Fertilization of an egg by motile sperm leads to the formation of the diploid sporophyte, which undergoes meiosis to produce haploid spores to restart the life cycle.