(A,B) Schematic diagrams of the transition division leading to the formation of a gametophore apical cell (A) or a filament apical cell (B). (C) A gametophore apical cell (left) versus a filament apical cell (right). A filament apical cell divides parallel to the parental caulonemal cell from which it is derived, and tip growth is directed from apical cells (green asterisk). The first division of the gametophore apical cell is always oblique and leads to the formation of an apical cell (blue asterisk) and a basal cell. Subsequent divisions of both the apical cell and the basal cell occur obliquely to the first division (D). Additional rotating divisions establish a tetrahedral apical cell (blue dot) that divides to both self-renew and produce phyllid apical cells (red asterisks) that direct growth of phyllids (E). Scale bars represent 20 µm. Images adapted from [12,14].