Haplopteris yakushimensis C. W. Chen & Ebihara

Haplopteris yakushimensis C. W. Chen & Ebihara, Phytotaxa 156 (4): 232. 2014. Fig. 1 Type. Japan. • Kagoshima Pref., Yakushima Island, Nakabase River, 20 Aug 1982, Nakaike s. n. (holotype TNS [VS-456666!]). Distribution and ecology. This species was previously recorded only in Japan and Taiwan (Chen et al. 2014, TPG 2019). In Vietnam, H. yakushimensis is found in damp evergreen broadleaf forests at elevations of 1200–1360 m, where it grows on rocks with thick compost near streams. Specimens examined. Vietnam. • Cao Bang Province: Phia-Oac Phia-Den National Park, 6 Dec 2013, Zhang et al. 6755 (MO, TAIF [499240!], VNMN). Phia-Oac Phia-Den National Park, Nguyen Binh District, Thanh Cong Ward, 22.589539°N, 105.880403°E, 1353 m, 8 Nov 2023, Chen Wade 6952 (TAIF!, VNMN!). • Ha Giang Province: Vi Xuyen District, Cao Bo Ward, 22.767500°N, 104.880394°E, 1200–1360 m, 12 Sep 2000, Harder et al. 5514 (UC [1763099!]). Note. Haplopteris, a fern genus comprising approximately 40 species, is primarily found in tropical Africa, Asia, and the Pacific Islands (Schuettpelz et al. 2016). In Vietnam, eight Haplopteris species were previously recorded: H. angustifolia (Blume) E. H. Crane, H. doniana (Mett. ex Hieron.) E. H. Crane, H. elongata (Sw.) E. H. Crane, H. ensata (Christ) C. W. Chen & S. Linds., H. ensiformis (Sw.) E. H. Crane, H. flexuosa (Fée) E. H. Crane, H. hainanensis (C. Chr. ex Ching) E. H. Crane, and H. sikkimensis (Kuhn) E. H. Crane (Chen et al. 2023). Haplopteris yakushimensis can be distinguished from these species by having fronds broader than 1 cm wide, costae that are grooved on the adaxial side and raised on the abaxial side, and the submarginal (ca. 1–2 mm away from the margins) sori lines. Recent studies have identified two genetically distinct yet morphologically indistinguishable lineages in H. yakushimensis (Kuo et al. 2017; TPG 2019). With the discovery of new populations in Vietnam, we are currently working to clarify these lineages using an integrated approach that includes reproductive biology, genome size estimation, and nuclear markers. The results of this research will be published in a separate paper.