1a	Annual, rhizome absent	2
1b	Perennial, rhizome present	5
2a	Glumes beset with long, patent hairs; disc shallowly lobed	S. rugosa
2b	Glumes glabrous; disc obsolete or tri-lobed	3
3a	Inflorescence spiciform, unbranched, lacking leafy bracts; disc obsolete	S. pergracilis
3b	Inflorescence paniculate, having a terminal and lateral panicles, leaf bracts present; disc tri-lobed	4
4a	Achene spherical with dark purplish beak, deeply pitted; disc lobe acuminate at apex	S. biflora
4b	Achene ellipsoid or subglobose with white beak, not deeply pitted; disc lobe acute at apex	S. parvula
5a	Plant much robust; achene cancellate; disc lobe obtuse or rounded at apex	S. terrestris
5b	Plant smaller; achene smooth or slightly rugulose; disc lobe acute at apex, often bidentate	S. levis