Background info on Physco biology and culture

Physcomitrella patens is a monoecious moss, which requires simple growth conditions for the completion of its life cycle. Moss gametophytes exist in two morphologically distinct forms: the juvenile filamentous tissue called protonema and the adult leafy tissue called gametophore. However, the molecular mechanism for the transition from the juvenile (protonema) to the adult (gametophore) stage is not precisely known.

This is a gametophore, with non-vascular leaflets (source Wikimedia commons).

gametophore [PO:0030018] A shoot system that consists of the shoot axes and non-vascular leaves of a plant in the gametophytic phase.