1	Rhizome with stiff, erect or suberect lateral branches, bearing spreading whorls of 5-10 fronds, forming thickets.		1 O. neriiformis
+	Rhizome creeping; fronds erect, scattered or in small clusters of 3-5		(2)
2 (1)	Rhizome not entirely covered with scales; scales with recurved apex; stipes dark brown.		2 O. wallichii
+	Rhizome entirely covered with overlapping scales; stipes stramineous		(3)
3 (2)	Rhizome scales spreading, narrowly triangular with a relatively wide apex, brown, central part of acumen not thickened; roots branching and with root hairs along their entire length; lamina glabrous on adaxial surface and margin.		3 O. undulata
+	Rhizome scales appressed to spreading, narrowly ovate-lanceolate with long narrow acumen with thickened central part; roots usually with glabrous, unbranched part ("rhizophore"); lamina hairy or glabrous		(4)
4 (3)	Phyllopodia very short, 1-2(-5) mm, mostly immersed in scales.		4 O. musifolia
+	Phyllopodia 2-6 cm.		5 O. cumingii