Revision of the fern genus Orthiopteris (Saccolomataceae) in Malesia and adjacent regions Author Luong, Thien Tam Department of Ecology - Evolutionary Biology, Viet Nam National University Ho Chi Minh city (VNUHCM) - University of Science. 227 Nguyen Van Cu, Ho Chi Minh City, Vietnam & Naturalis Biodiversity Center, section Botany. PO Box 9517, 2300 RA Leiden, The Netherlands Author Hovenkamp, Peter H. Naturalis Biodiversity Center, section Botany. PO Box 9517, 2300 RA Leiden, The Netherlands Author Sosef, Marc S. M. Botanic Garden Meise, Nieuwelaan 38, 1860 Meise, Belgium text PhytoKeys 2015 2015-07-21 53 39 71 http://dx.doi.org/10.3897/phytokeys.53.4955 journal article http://dx.doi.org/10.3897/phytokeys.53.4955 1314-2003-53-39 824BD167D1535A15FC27FF98FFD3A404 576284 7. Orthiopteris tenuis (Brack.) Brownlie, Nova Hedwigia 55 (Pterid. Fl. Fiji): 115. 1977. Figs 3e, f, k Microlepia tenuis Brack., U.S. Expl. Exped., Filic. 16: 236. 1854. Microlepia papillosa Brack. U.S. Expl. Exped., Filic. 16: 237, t. 34, fig. 1. 1854. Type. FIJI. U.S South Pacific Exploring Expedition s.n. (number 4 in Brackenridge 1854 ) (Holo: US, 00134882*[http://plants.jstor.org/stable/10.5555/al.ap.specimen.us00134882]; iso: K, 000794859*). Saccoloma tenue (Brack.) Mett., Ann. Sci. Nat., Bot. ser . 4, 15: 80. 1861. Type. Based on Microlepia tenuis Brack. Saccoloma papillosa (Brack.) Mett., Ann. Sci. Nat., Bot. ser . 4, 15: 80. 1861. Type. Based on Microlepia papillosa Brack. Type. FIJI. U.S South Pacific Exploring Expedition s.n. (number 3 in Brackenridge 1854 ) (Holo: US, 00134883* [http://plants.jstor.org/stable/10.5555/al.ap.specimen.us00134883]; iso: K & NY, K000794860*, NY 00127936*). Description. Rhizome erect, rising at 5-60 cm above ground, diameter 1.5-10 cm. Rhizome scales pseudopeltate, 4-8 x 0.7-1 mm, narrow, linear lanceolate, usually falcate and suddenly contracted into a long thin acumen. Fronds 100-170 x 40-50 cm ; stipes slender, 30-70 cm long, 0.3-0.8 cm across (at base), dark brown; lamina deltoid, widest at base, tripinnate, sometimes quadripinnate in large plants, ca. 70 x 40 cm, herbaceous, lively green when dry, glabrous; pinnae at 35-45° to rachis, largest at base, separated or slightly overlapping, stalk 1-2 cm, including stalk up to 26 x 12 cm, lanceolate, first basiscopic pinnules of lowest pinnae enlarged; ultimate segments 1.5-2.0 x 0.7-1.0 cm, sessile or very short stalked, trapezoid to narrowly so near frond apex, apex obtuse to acute or attenuate, margin with weak cartilaginous border; shallowly to deeply incised to 0.2-2.0 mm (see discussion) from veins; lobes acute, veins in lobes with 1-3 forks, bright green, strongly contrasting to the lamina, percurrent, sometimes ending just below apex. Scales on rachis absent, absent. Sori apical on small lobes, lateral on larger lobes, asymmetric, sometimes symmetric, not reflexed, in one plane with lamina wings, ca. 1.5 x 1 mm, funnelform, sometimes ovate, widest at middle to 2/3 from base; inner indusium yellow bright green, contrasting in colour with lamina, firm, 1/2-2/3 as long as outer indusium, apex with obtuse to acute lobe, slightly eroded, ca. 0.25-0.5 the length of inner indusium; outer indusium obtuse, sometimes acute, truncate or emarginate with 1-2 shallow sinuses; sporangia 7-10 per sorus, capsule globose and rounded at apex, gradually narrowed toward base, indurated annulus cells 17-22, +/- equal; spores in polar view 30-35 µm , in lateral view 25-27 µm . Distribution. Endemic to Fiji (Viti Levu, Vanua Levu, Ovalau). Ecology. Terrestrial, dense forest, bank along stream, at 0-1000 m altitude. Discussion. This species is highly variable in terms of frond dissection, and sorus shape. Plants from higher altitudes (above ca. 500 m) have larger fronds and furthermore differ from the lowland plants in ultimate segments being deeply incised (distance of lamina from base of sinuses to costules less than 0.5 mm), and sori with almost equally long inner- and outer indusium. In contrast, the lowland plants have ultimate segments more shallowly incised (distance of lamina from base of sinuses to costules more than 0.5 mm), and sori with a large difference in length between inner and outer indusia. We could not separate the two forms because of the presence of intermediate specimens.