1	"Erect black branches present or absent; internode showing 4–12 cortical vascular bundles in cross-section; leaf sheath open; bracts enclosing anthers narrowly triangular"	Heterozostera
1	"Branches never erect; internode showing 2 cortical vascular bundles; leaf sheath open or closed; bracts enclosing anthers broadly triangular"	Zostera