Leptochilus luangprabangensis Liang Zhang, Khamphanh Thepkaysone & Zhuo Zhou

Zhang, Liang, Lu, Ngan Thi, Zhou, Xin-Mao, Zhou, Zhuo, Thepkayson, Khamphanh, Luong, Thien Tam & Zhang, Li-Bing, 2024, Exploring the diversity of the Java fern genus Leptochilus (Polypodiaceae) in the Indo-Burma Biodiversity Hotspot, Phytotaxa 659 (3), pp. 213-235 : 224

6. Leptochilus luangprabangensis Liang Zhang, Khamphanh Thepkaysone & Zhuo Zhou , sp. nov. ( Fig. 8 ).

Type: LAOS. Luang Prabang: near Luang Prabang City , elev. 586 m, 19.83°N / 102.15°E, on a small tree trunk in limestone mountain, 13 May 2019, Zhuo Zhou & Liang Zhang LZ 415 (holotype KUN-1576324!; isotypes KUN!) .

Diagnosis: Leptochilus luangprabangensis is characterized by its climbing habit, the length of fertile and sterile fronds nearly identical, thin lamina texture, and sterile fronds shortly petiolated.

Plants perennial, evergreen, epiphytic. Rhizome long creeping, ca. 2.5–3.0 mm in diam., dorsiventrally flattened, scaled, with a few short phyllopodia and roots. Apex of rhizome and basal petiole densely scaly, scales subulatelanceolate, 1.4–2.4 × 0.3–0.7 mm, brown, basifixed, concolorous, clathrate, margin entire or sparely denticulate, apex acuminate. Fronds dimorphic, sterile fronds larger than fertile fronds. Sterile fronds 12–18 cm tall, laminae much longer than petioles; laminae ribbon-lanceolate, base cuneate, apex acuminate, 10–16 cm long, 2.0– 3.1 cm wide at middle, chartaceous, glabrous; petioles stramineous, grooved adaxially, glabrous, 0.6–0.8 mm in diam., 0.6–1.7 cm long. Fertile fronds 14–17 cm tall, petioles shorter than laminae; laminae elliptic-lanceolate, margins entire, base cuneate, apex long acuminate, 11–13 cm long, 1.3–1.5 cm wide at middle, thinly chartaceous, glabrous; petioles stramineous, grooved adaxially, glabrous, 0.5–0.7 mm in diam., 3–4 cm long. Veins anastomosing, lateral veins visible, veinlets invisible. Sori linear, reach lamina margins, ca. 0.5 mm from margins and 0.4 mm from midrib, 25–28 on each side of midrib, 0.7–0.9 cm long, 0.4–0.6 mm wide when mature, at angles of 36–45 degree with midribs, centers ca. (1–) 3–4 mm apart from one another. Paraphyses absent.

Distribution and habitat: Leptochilus luangprabangensis is known from a single collection made in the limestone forest near the capital city of Luang Prabang Province, Laos. The species was observed growing as a hemiepiphyte on a small tree trunk. It was anchored to the tree with rhizomes and roots, and the roots extended into the soil below.

Etymology: The species is named after Luang Prabang Province, Laos, where it was discovered.

Note: Morphologically, Leptochilus luangprabangensis is most similar to L. chingii Liang Zhang & Li Bing Zhang (2018: 173) due to their simple and slightly dimorphic fronds, lanceolate laminae, and laminae gradually narrowed towards base. However, they differ in the lamina texture (thinly chartaceous vs. chartaceous or thickly chartaceous in L. chingii and petiole length of sterile fronds (0.6–1.7 cm vs. (0.5–) 2–5 cm). Additionally, L. luangprabangensis has only been observed growing as a hemiepiphyte on tree trunks, while L. chingii was found on moist rocks. Though L. luangprabangensis is phylogenetically the closest to L. vietnamensis , they have 12 bp differences in 3074 bps of aligned three plastid markers ( Zhang et al. 2024). Morphologically, L. luangprabangensis has fertile fronds nearly the same length as sterile fronds that are 12–18 cm long, while L. vietnamensis has fertile fronds much shorter than the sterile fronds that are 30–40 cm.

Figures

FIGURE 8. Leptochilus luangprabangensis Liang Zhang & Zhuo Zhou,—A. Habitat.—B & C. Habit.—D. Abaxial view of portion of fertile lamina.—E. Abaxial view of fertile frond and sterile frond.—F. Rhizome. Photo credit: Liang Zhang.