Table 2.

Comparison of stomatal traits in genera of Gnetales (see also Fig. 10)

	Ephedra	Gnetum	Welwitschia
Leaves	Reduced, scale-like	Petiolate; elliptical lamina with a central midrib and reticulate venation	Long-lived, linear, strap-like with parallel venation
Stomatal location	In linear cell files on stem; also sparsely present on leaves	On abaxial leaf surface	On both leaf surfaces
Stomatal origin	(On stems) stomata derived from intercalary meristem above each node	Most stomata derived from expanding intercostal regions throughout lamina	Stomata derived from intercalary meristem at leaf base
Epidermal prepatterning	Linear	Quartet	Linear
Guard mother cell (GMC) formation	GMCs formed directly from meristemoids	Each GMC formed from central cell of a triad formed by two successive mitoses of a meristemoid	Each GMC formed from central cell of a triad formed by two successive mitoses of a meristemoid
Guard cell (GC) orientation	Non-random; long axes of GCs parallel with organ axis	Initially non-random; stomata oriented in regular pattern parallel or perpendicular; later disrupted	Non-random; long axes of GCs parallel with leaf axis
Mature stomata	GCs deeply sunken, overarched by LSCs; GC length ~25–40 µm	GCs flush with surface or slightly raised; GC length ~20 µm	GCs deeply sunken, overarched by LSCs; GC length ~40 µm
Lateral neighbour cells/lateral subsidiary cells (LSCs)	Perigene; derived from oblique divisions in lateral neighbour cells in adjacent cell files	Mesogene; GMC and initial pair of LSCs together form a triad	Mesogene; GMC and pair of LSCs together form a triad