Ann. Bot. Fennici 46: 381–388 ISSN 0003-3847 (print) ISSN 1797-2442 (online) Helsinki 30 October 2009 © Finnish Zoological and Botanical Publishing Board 2009 Hainan tree ferns (Cyatheaceae): morphological, ecological and phytogeographical observations Shi-Yong Dong South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China (e-mail: [email protected]) Received 27 Aug. 2007, revised version received 4 June 2008, accepted 6 June 2008 Dong, S. Y. 2009: Hainan tree ferns (Cyatheaceae): morphological, ecological and phytogeo- graphical observations. — Ann. Bot. Fennici 46: 381–388. Based on extensive field surveys and studies of numerous herbarium collections, a taxonomic revision on the tree ferns (Cyatheaceae) from Hainan Island, South China is made. Some formerly used diagnostic characters are critically reassessed, while others with taxonomic value are introduced for the first time. As a result, two genera and six species are recognized for the island. Alsophila denticulata is a new record for Hainan. Alsophila gigantea var. polynervata and Cyathea hainanensis are reduced to synonymy. A lectotype is designated for Alsophila podophylla. The habitat and geo- graphical distribution of the Hainan tree ferns are briefly discussed. Their distribution patterns indicate affinities either to the fern flora of Malesia, the eastern Himalayas, or southern Japan. Key words: Cyatheaceae, distribution, floristics, lectotype, taxonomy Introduction ferns by having trunk-like, erect stems. World- wide there are about 500 extant species in the Hainan, an island in the South China Sea, lies tropics and subtropics (Tryon & Gastony 1975). between 18°9´–20°11´N and 108°36´–111°4´E, In Asia, tree ferns are concentrated in Malesia; and has an area of 33 600 km2 (R. Z. Zhang 14 species are known in China (X. C. Zhang 2004). It is the second largest island in China, 2004), of which six occur in Hainan Island. and abounds in pteridophytes. However, the Originally, Ching and his students (Ching & pteridophyte flora is not well documented Wang 1959, 1964, Ching et al. 1964) recognized because there is no modern revision since Flora six locally endemic and three widely distributed Hainanica vol. 1 (Ching et al. 1964). In order tree ferns. Except for Sphaeropteris hainanensis, to revise the fern flora of Hainan, we made Xia (1989) reduced five of these Hainan endem- intensive explorations throughout the island, and ics to synonyms of very common tropical Asian checked all Hainan fern specimens in the major taxa. More recently, X. C. Zhang (2004) treated Chinese herbaria. The present paper is a study S. hainanensis as conspecific with S. brunoni- contributing to this revised flora. ana, but Wu (2006) kept it as a separate species. Plants of the family Cyatheaceae, usually Besides S. hainanensis, another taxon, Alsophila called tree ferns, are distinct from most other gigantea var. polynervata is also controversial 382 Dong • ANN. BOT. FeNNICI Vol. 46 because this variety, represented only by a single STipe pneumaThodeS. Pneumathodes occur herbarium sheet, was thought to be distinct by along each side of the stipe and rachis and often having more veins in its lobes than the name provide distinctive characters in Cyathea, unfor- variety (Miau 1980, Xia 1989). tunately they are usually not seen in herbarium Due to their very large lamina, which cannot specimens (Holttum 1963). The presence of be pressed as a single herbarium specimen, and either discontinuous or nearly continuous pneu- insufficient field observations, the taxonomy of mathodes was used as a key character to separate Hainan Cyatheaceae is not yet clear. Many mor- Sphaeropteris from Alsophila by Xia (1989). phological characters, especially those seen in Our observations show that the shape of pneu- the living state, as well as habitat and distribu- mathodes is useful in the classification of species tional data are hitherto not well documented. but cannot be used to divide groups at the level of genus. Actually, nearly continuous pneumath- odes occur not only in Sphaeropteris but also in Morphological and taxonomical some species of Alsophila, e.g., A. latebrosa. treatment lamina ouTline. In most Hainan tree ferns the outline of the lamina is broadly lanceolate, As mentioned by Holttum (1965) and Xia (1989), i.e., broadest in the middle and gradually nar- some characters such as structure of stipe scales, rowing towards the base and the apex. Alsophila the presence and shape of indusia, and the number denticulata is the notable and only exception, of spores in a sporangium are stable and useful and has a triangular lanceolate lamina with the in the taxonomy down to the subgeneric level. base broadest. Besides the overall shape of the Below we list some other characters that we con- lamina, its distal part also differs among species. sider useful for species delimitation, but which A pinnate and gradually narrowing apex is the were either neglected or not well understood in common pattern for the majority of taxa, though previous taxonomical works on Cyatheaceae. in A. podophylla, the distal part is usually a Trunk heighT. The height of the trunk sepa- pinna that is conform to the lateral pinnae. rates Hainan tree ferns in two distinct groups. pinna arrangemenT along The rachiS. The Sphaeropteris brunoniana, A. spinulosa, and A. arrangement of the pinnae along the rachis is latebrosa are arborescent with trunks that can useful to distinguishing different tree ferns in reach over 5 m high (for S. brunoniana, we the field.Alsophila latebrosa and A. gigantea are recorded an extreme of 16 m). The other three characterized by mostly opposite lateral pinnae species, A. podophylla, A. denticulata and A. (except those near the apex). In the other species, gigantea are shrub-like, with trunks usually less the pinnae are generally alternate but the lower than 3 m high. 1–3 pairs of pinnae are sometimes subopposite. STipe color. This is a valuable character for This character helps to distinguish two shrub- the classification of Hainan tree ferns. Basically, like and very common species, A. gigantea and three colors i.e., black, dark red and green, are A. podophylla, from a distance. found in this group. The stipe of A. gigantea is peTiolule lengTh of baSal pinna. This char- black, that of A. podophylla, A. spinulosa, and A. acter usually cannot be seen in herbarium collec- denticulata is dark red, and the stipe of A. lateb- tions and its taxonomical value has seldom been rosa and S. brunoniana is green when young and noticed. In Hainan tree ferns it shows three char- turns brown when very old. acter states. The basal pinna has either a long STipe SpineS. Though spines are not always petiolule, from 2 to 8 cm, in A. podophylla and present on the stipe in every tree fern, we found S. brunoniana, a short stalk less than 2 cm, in A. it a useful character. Among the Hainan tree denticulata and A. spinulosa, or is not petiolulate ferns, A. spinulosa is the only species with at all in A. gigantea and A. latebrosa. obvious, long and sharp spines on the stipe and VeinS. Veins single or 2-forked was one of the rachis. In the other species, stipes are usually characters used to distinguish subgenus Alsophila spineless though occasionally there are some from subgenus Gymnosphaera by X. C. Zhang short spines at the base of the stipes. (2004). In Zhang’s opinion, veins are single in ANN. BOT. FeNNICI Vol. 46 • Hainan tree ferns (Cyatheaceae) 383 subgenus Gymnosphaera but usually 2-forked in Cyathea hainanensis Ching, Acta Phytotax. Sin. 8: 147, subgenus Alsophila. Our observations show that 168, pl. 21. fig. 23. 1959. — Sphaeropteris hainanensis (Ching) R. M. Tryon, Contr. Gray Herb. 200: 21. 1970. — this character cannot be used at the subgeneric Type: China. Hainan, Sanya, H.-Y. Liang 62675 (holotype level. For instance, the veins are single or more PE!; isotype IBSC!). often 2-forked in A. denticulata, which belongs to Cyathea contaminans auct. non Copel.: Chun et al., Fl. subgenus Gymnosphaera. Hainan. 1: 139. 1964. SoruS poSiTion and number. The position and the number of sori in a lobe are generally habiTaT. On road sides in forest areas or in stable and distinctive in a given species. Sori valley forest, alt. 270–1250 m. are medial in A. denticulata and S. brunoniana, diSTribuTion. China (Hainan, Xizang, or close to the costule as in A. spinulosa. An Yunnan), India, Bhutan, Sikkim, Bangladesh, interesting case of soral arrangement is found in Myanmar, Vietnam (Fig. 1). A. gigantea, where sori are medial on the basal Trunk 5–10(16) m high; stipe-scales light veinlets but become gradually closer to the cos- brown to nearly white, with regular black setae tule on distal veinlets, consequently sori in a lobe along the margins; stipes green or brown, with- form a V shape. The number of sori in a lobe out spines or rarely with few and short spines at varies from 2 to 11 in different species. the base; pneumathodes on either side of stipe nearly continuous; lamina broadly lanceolate, Key to Hainan tree ferns the middle part broadest, 2-pinnate and gradu- ally narrowed towards apex; pinnae 18–24 pairs, 1. Scales at base of stipe light brown, almost transparent, alternate or sometimes lower 3–4 pairs suboppo- consisting of uniform cells with minute dark spines site; petiolules of basal pinnae 2–7 cm long; pin- along the margin (genus Sphaeropteris) ......................... .................................................................. S. brunoniana nules deeply lobed, some needle-like hairs abax- 1. Scales at base of stipe brown to dark brown, not trans- ially on pinnule-costule; veinlets 3-branched parent, median cells more compact and darker brown or 2-branched in two times; sori exindusiate, than marginal cells (light brown), scale margin usually medial, often 6 pairs per lobe.