Oleandra

Hovenkamp, Peter H. & Ho, Boon-Chuan, 2012, A revision of the fern genus Oleandra (Oleandraceae) in Asia, PhytoKeys 11, pp. 1-37 : 6-7

Oleandra

Oleandra Cav., Anales Hist. Nat. 2: 115. 1799; Descr. Pl. (Cavanilles): 252. 1802. Lumbreras, Flora Montiber. 28: 19. 2004. Aspidium subg. Oleandra Splitg., Tijdschr. Natuurl. Gesch. Physiol. 7: 411. 1840. Type: Oleandra neriiformis Cav. (as “neriformis”).

Ophiopteris Reinw., Syll. Pl. Nov. 2: 3. 1825. Type: Ophiopteris verticillata Reinw., = Oleandra neriiformis .

Neuronia D.Don, Prodr. Fl. Nepal.: 6. 1825. Type: Neuronia asplenioides D.Don, = Oleandra wallichii .

Description.

Terrestrial, epilithic or epiphytic, creeping or scrambling ferns. Rhizome scaly, roots scattered, often with long rhizophore-like proximal parts, fronds scattered or in whorls, on stipe-like phyllopodia, dehiscing at a slightly thickened articulation point. Fronds stipitate, lamina simple, margin entire, veins distinct, somewhat raised on both sides, 1-2 ' forked at or near the costa, costa often with narrow scales, lamina and veins often with acicular or capitate hairs. Sori in one, often irregular row on each side of the costa, with a more or less reniform, glabrous or hairy indusium. Sporangia stalked, stalk often with a number of sessile or stalked glands below the sporangium, sporangium body glabrous, spores monolete, perispore with broad wings, sometimes highly perforate, or echinate, massive.

Key to the 9 Asian species

1	Rhizome with stiff, erect to pendent rootless aerial branches	2
-	Rhizome creeping	4
2	Fronds strongly dimorphic, scattered on the rhizome or somewhat clustered on short side branches	9 Oleandra werneri
-	Fronds monomorphic or slightly dimorphic, often in whorls of 5-10 fronds	3
3	Lamina thick, coriaceous, costa with copious, conspicuous, 3-4 mm long pale to brown scales on the abaxial surface	1 Oleandra coriacea
-	Lamina thin, papyraceous when dry, costa mostly with few or inconspicuous scales on the abaxial surface	4 Oleandra neriiformis
4	Rhizome in older parts not entirely covered with scales; scales with squarrose acumen and entire or distinctly glandular margin	5
-	Rhizome entirely covered with overlapping scales; scales with appressed or spreading apex, usually with non-glandular cilia	6
5	Rhizome scales with gradually narrowed apex, stipes 0.5-4.5 cm long, costa and stipe often with distinct dark colouration on the abaxial surface	5 Oleandra sibbaldii
-	Rhizome scales with abruptly narrowed apex, stipe to 2-3 mm long, costa and stipe without dark colouration on the abaxial surface	7 Oleandra vulpina
6	Phyllopodia, inconspicuous, 2-5 mm, rarely 1 cm long, much shorter than the stipe, sori mostly in a closely costal single row	7
-	Phyllopodia, conspicuous, 2-10 cm long, often as long as or longer than the stipe, position of sori costal to medial	8
7	Rhizome scales squarrose, costa and stipe usually with dark colouration, frond apex distinctly apiculate	8 Oleandra wallichii
-	Rhizome scales appressed, costa and stipe without dark colouration, frond apex acute to acuminate	3 Oleandra musifolia
8	Rhizome scales spreading, long triangular with a wide acumen, brown, central part not conspicuously thickened, roots branching with root hairs over their entire length; lamina glabrous on upper surface and margin	6 Oleandra undulata
-	Rhizome scales appressed to spreading, narrowly ovate-lanceolate with long narrow acumen, central part dark, thickened, roots often with glabrous, unbranched part ( “rhizophore”), lamina hairy or glabrous	2 Oleandra cumingii