THAI FOR. BULL. (BOT.) 40: 102–104. 2012. A new species of Rhachidosorus (Rhachidosoraceae), a genus new to Thailand STUART LINDSAY*, DAVID J. MIDDLETON* & PIYAKASET SUKSATHAN** ABSTRACT. The genus Rhachidosorus is newly recorded for Thailand and the species Rhachidosorus siamensis S.Linds. is described. KEY WORDS: Rhachidosorus, Rhachidosoraceae, fern, Thailand. Rhachidosorus is a genus of about seven anadromic. Veins free, forked or pinnate. Sori species from East and Southeast Asia, from Japan oblong, narrowly elliptic or elongate, mostly on to Sumatra and the Philippines (Christenhusz et al., acroscopic veins in ultimate segments; indusia 2011). The genus has been variously placed in membranous, oblong or elongate, attached on one Athyriaceae (e.g., Chu et al., 1999), Woodsiaceae side along veins. Spore surface muriform or with (e.g., Smith et al., 2006, 2008) and, most recently, warty projections. in Rhachidosoraceae (Christenhusz et al., 2011; About seven species from East and Southeast Rothfels et al., 2012). On a joint expedition of the Asia, from Japan to Sumatra and the Philippines. Royal Botanic Garden Edinburgh and the Queen Sirikit Botanic Garden in 2009 a fern was collected in Doi Pha Hom Pok National Park in Chiang Mai RhachidosorussiamensisS.Linds., sp. nov. Similar Province which proved not only to be a new record toRhachidosorusblotianus Ching but differing in of the genus Rhachidosorus for Thailand but a new darker stipe and rachis, lamina much less divided species in the genus. and sori more remote from costule/costulet. Typus: Thailand, Chiang Mai, Fang District, Doi Pha Hom Descriptions of the genus and the new species Pok National Park, trail from Kew Lom Ranger are given below. Substation to Pang Mong Kon, 1750 m altitude, 20º3’56’’ N, 99º8’6’’ E, in shady gully of small RHACHIDOSORUS stream in lower montane forest on granite bedrock, 2 October 2009, D.JJJ. Middleton, S. Lindsay & P. Ching, Acta Phytotax. Sin. 9: 73. 1964; Chu et al., Suksathan5051 (holotype QBG; isotypesBKF,E, Fl. Reipubl. Popularis Sin. 3(2): 267. 1999. P). Fig. 1. Terrestrial or lithophytic, medium-sized to Terrestrial. Rhizome ascending, 2–3 cm di- large ferns. Rhizome creeping, ascending or erect, ameter (when fresh), producing a mass of fi brous scaly; scales brown, clathrate or only weakly so, roots; scales on rhizome and stipe very variable in sometimes of quite disparate shapes and sizes but shape and size, brown or golden brown, weakly generally narrowly triangular to linear, margin clathrate with elongate cells, narrowly triangular to entire, basally attached. Frondd with distinct stipe linear, often rather crisped, 2–14 x 0.1–2.3 mm. and lamina.Stipes not thickened at base, not winged. Fronds to 113 cm long. Stipe and rachis mid to Laminae bipinnate to tripinnate or quadripinnati- dark green above, very dark green to black beneath fi d, rarely pinnate; pinnae usually not opposite, * Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR, Scotland, U.K. Email: [email protected] ** Herbarium, Queen Sirikit Botanic Garden, P.O. Box 7, Mae Rim, Chiang Mai 50180, Thailand. A NEW SPECIES OF RHACHIDOSORUS (RHACHIDOSORACEAE), A GENUS NEW TO THAILAND (S. LINDSAY , D.J. MIDDLETON1 & P. SUKSATHAN)103 (distinction less obvious when dry), stipe 20–36 previously included. See Rothfels et. al (2012) for cm long, densely scaly at base, becoming sparser the differences that are now recognised between towards rachis and into rachis. Lamina mid to dark Rhachidosoraceae, Athyriaceae and Woodsiaceae. green and slightly shiny above, much paler beneath, 47–78 x 18–36 cm, bipinnate to tripinnate, ovate in ACKNOWLEDGEMENTS outline, apex acuminate, formed from progressively smaller and closer pinnae without a distinct terminal We thank the Leverhulme Trust and Queen pinna; rachis ± terete but with a narrow wing on Sirikit Botanic Garden for the funding for this either side visible from above, each with a thickened work; the director and staff of Doi Pha Hom Pok margin, with linear scales and short glandular National Park for their logistical support in the hairs; 18–22 pairs of free pinnae, 3.5–12 cm apart fi eld; and Dr Harald Schneider for helpful near base, triangular, apex acuminate, largest pinnae discussions. towards base but not basal, 9.8–20 x 2.9–8.7 cm, stalked for 4–8 mm; axes winged, wings with REFERENCES thickened margins which are sometimes also slightly Christenhusz, M.J.M., Zhang, X-C. & Schneider, inrolled, lowest pinnae refl exed or not; ultimate H. (2011). A linear sequence of extant families segments ovate to elliptic, dentate, apex obtuse to and genera of lycophytes and ferns. Phytotaxa acute, glabrous above, with many scattered short 19: 7–54. glandular hairs on veins and lamina beneath; vena- tion clearly visible, veinlets not reaching margin Chu Wei-ming, Wang Zhong-ren, Hsieh Yin-tang and with enlarged endings visible above. Sori & He Zhao-rong (1999). Athyriaceae. In: Chu oblong or narrowly elliptic, mostly on acroscopic Wei-ming, ed., Fl. Reipubl. Popularis Sin. 3(2): veins, one per pinnule lobe, basal lobes often larger 32–504. Science Press, Beijing and then with sori on both acroscopic and basiscopic Rothfels, C.J., Sundue, M.A., Kuo, L.-Y., Larsson, veins and opening towards each other, 2–4 mm A., Kato, M., Schuettpelz, E. & Pryer, K.M. long, more or less equidistant from costule/costulet (2012). A revised family-level classifi cation (depending on whether frond is bipinnate or tripin- for eupolypod II ferns (Polypodiidae: nate) and segment margin; indusia pale green, often Polypodiales). Taxon 61: 515–533. translucent, margin slightly darker and minutely Smith, A.R., Pryer, K.M., Schuettpelz, E., Korall, irregular to fi mbriate.Spore surface muriform. P., Schneider, H. & Wolf, P.G. (2006). A clas- Distribution.— Only known from the type sifi cation of extant ferns. Taxon 55: 705–731. locality. Smith, A.R., Pryer, K.M., Schuettpelz, E., Korall, Ecology.— Terrestrial on clay bank in shady P., Schneider, H. & Wolf, P.G. (2008). Fern gully of small stream in lower montane forest on Classifi cation. Pp. 417–467 In: Ranker, T.A. & granite bedrock at 1750 m. Haufl er, C.H. (eds), Biology and Evolution of Ferns and Lycophytes, CUP, Cambridge. Note.— In the key to fern families in the Tagawa, M. & Iwatsuki, K. (1979). In: Smitinand, Flora of Thailand (Tagawa & Iwatsuki, 1979) T. & Larsen, K. (eds), Flora of Thailand 3 (1). Rhachidosorus siamensis would key out to Royal Forest Department, Bangkok. Athyriaceae, a family in which the genus was 104 THAI FOREST BULLETIN (BOTANY) 40 A B C D E F Figure 1.Rhachidosorus siamensis S.Linds. A. Habit; B. Whole frond from above; C. Rachis and pinna above; D. The same rachis and pinna beneath; E. Pinnule with sori; F. Scales on crozier. All photos from Middleton et al. 5051. A by Piyakaset Suksathan, B–F by David J. Middleton.