Hymenasplenium phamhoanghoi Li Bing Zhang, K.W. Xu & T.T. Luong, 2018

Hymenasplenium phamhoanghoi Li Bing Zhang, K.W. Xu & T.T. Luong View in CoL , sp. nov. Figs. 8 View FIGURE 8 , 9 View FIGURE 9 .

Type:— VIETNAM. Khánh Hòa: Hòn Bà Nature Reserve , trail at 32nd km of main road toward Yersin’s house, 12°01’45”– 12°12’00”N, 102°53’45”– 109°02’34”E, elev. 1100 m, 26 October 2015, Li Bing Zhang, Xinmao Zhou, Thien Tam Luong, Minh Tri Dang, Bich Ha Duong 8819 (holotype CDBI! GoogleMaps , isotypes MO! GoogleMaps , PHH! GoogleMaps ).

Diagnosis:— Hymenasplenium phamhoanghoi is most similar to H. unilaterale (Lamark 1786: 305; Hayata 1927: 712) in having pinna teeth entire, veins terminating in the marginal teeth and reaching nearly apex of teeth, but the former has pinnae rectangular or trapeziform, pinna apex obtuse or acute, and bases of acroscopic pinnae with auricles, while the latter has pinnae falcate or trapeziform, pinna apex acute or acuminate, and bases of acroscopic pinnae without auricles.

Plants perennial, evergreen, up to 40 cm tall. Rhizomes long creeping, ca. 4 mm in diam., apex scaly, scales dark brown, narrowly triangular or lanceolate, margins nearly entire, 1–3 × 0.3–0.5 mm; root dark brown when dried, slender, up to 9 cm long, ca. 0.2 mm in diam, rhizome and root often glabrous, rarely with sparsely brown woolly indument. Fronds remote, up to 20 mm apart, herbaceous; petioles shiny, dark brown, base near rhizome sparsely covered with scales, scales small, 0.1 × 0.4 mm, lanceolate, brown, margins nearly entire. Laminae narrowly ovate, 1- pinnate, 15–25 × 4–6 cm, base slightly reduced, widest near base, gradually narrowing toward apex, apex acuminate; rachises 1 mm in diam., glabrous, shiny, dark brown, adaxial side grooved and with 2 green narrow wings. Pinnae shortly stalked to almost sessile at apex, 20–30 pairs, alternate, rectangular or trapeziform, (middle pairs) 2.5–3 × 0.5–0.8 cm, about 2–4 mm apart, base asymmetrical, acroscopic side truncate and subparallel or forming an angle less than 15° with rachis, basiscopic side cuneate, with 15–20 mm absent (calculated from the base to the first tooth appearing in the margin of basiscopic side), acroscopic margins serrate, teeth not retuse, acute or obtuse, basiscopic margins entire at base, serrate in the middle and apex; pinna apex acute or obtuse. Veins visible on both sides of pinnae, green, rarely brown near pinnae petioles, lateral veins visible on both sides of pinnae, green, forking and terminating in marginal teeth, 3–4 basal basiscopic veins lacking. Sori linear, 2–3 mm long, medial to supramedial, (1–)5–7 on acroscopic side and 1–3 on distal basiscopic side of the pinnae in the middle part of the laminae, centers 2–4 mm apart from one another; indusia brown, linear, membranous, entire, opening toward costa.

Geographical distribution:— Hymenasplenium phamhoanghoi is currently only known from Hòn Bà Nature Reserve, Khánh Hòa Province, southern Vietnam. It is likely endemic to Vietnam.

Ecology:— Hymenasplenium phamhoanghoi was observed to grow in acidic soils under evergreen forest.

Etymology:—The species epithet is in honor of Prof. Phạm Hoàng Hộ for his great contributions to the fern flora of Vietnam (e.g., Pham 1991, 1999).

Vernacular name:— ħflůďäffǎ (nan yue mo ye tie jiao jue).

Taxonomic notes:—Morphologically, Hymenasplenium phamhoanghoi is different from any members of Hymenasplenium from Southeast Asia in having pinna apex obtuse, bases of acroscopic pinnae with auricles, pinna teeth entire, and veins terminating in the marginal teeth and reaching nearly apex of teeth. In our molecular analysis, H. phamhoanghoi formed a well supported clade with H. unilaterale and some unidentified material from Australia and Pacific islands. These relationships are supported by their similar characters of pinna teeth and veins.