Hymenasplenium distans Li Bing Zhang, K.W. Xu & Liang Zhang, 2018

Xu, Ke-Wang, Zhang, Liang, Lu, Ngan Thi, Zhou, Xin-Mao, He, Hai, Luong, Thien Tam, Knapp, Ralf, Liao, Wen-Bo & Zhang, Li-Bing, 2018, Nine new species of Hymenasplenium (Aspleniaceae) from Asia, Phytotaxa 358 (1), pp. 1-25 : 7-10

Hymenasplenium distans Li Bing Zhang, K.W. Xu & Liang Zhang , sp. nov. Figs. 4 , 5 .

Type:— VIETNAM. Hoa Binh: Ngoc Son Ngo Luong Nature Reserve , 26°25’53”N, 106°2’30”E, elev. 1350 m, 20 November 2013, Li Bing Zhang, Liang Zhang & Lu Thi Ngan 6296 (holotype CDBI! , isotypes MO! , VNMN! ).

Diagnosis:— Hymenasplenium distans is most similar to H. apogamum ( Murakami & Hatanaka 1988: 193; Nakaike 1992: 841) in having pinnae quadrangular-trapeziform in outline, entire on tooth margins, spreading or deflexed at base, obtuse at apex, usually crispate at base auricle, but the former has petioles black, fronds up to 15 mm apart, and the ratio of laminae to petioles near 0.5, while the latter has petioles brown, fronds 2–3 mm apart, and the ratio of laminae to petioles near 1.

Plants perennial, evergreen, 35–40 cm tall. Rhizomes short creeping, ca. 1–2 mm in diam., apex scaly, scales dark brown, narrowly triangular, margins nearly entire, 0.5–1 × 2.5–3.5 mm; root stramineous when dried, up to 8 cm long, ca. 1 mm in diam, with orange-brown woolly indument or subglabrous. Fronds remote, up to 15 mm apart, herbaceous; petioles shiny, black, 15–26 cm long, ca. 1.2 mm in diam., base sparsely covered with scales similar to those on rhizome, or subglabrous. Laminae ovate, 1-pinnate, 14–18 × 4.5–8 cm, widest near base, gradually narrowing toward apex, apex subacute; rachises ca. 1 mm in diam., subglabrous, shiny and black abaxially, adaxial side grooved and with 2 grayish green narrow wings. Pinnae almost sessile to shortly stalked with rachis color extending onto the base of costa abaxially, 15–25 pairs, opposite or subopposite at the base of laminae, alternate in the middle and apex, lower pinnae deflexed toward stipe, quadrangular-trapeziform, (middle pairs) 3–3.5 × 0.7–1 cm, about 0–2 mm apart, base asymmetrical, acroscopic side truncate and subparallel or forming an angle less than 15° with rachis, subauriculate, basiscopic side cuneate, with 5–15 mm absent (calculated from the base to the first tooth appearing in the margin of basiscopic side), acroscopic margins sinuate to serrate, teeth acute, not retuse, basiscopic margins entire at base, sinuate to serrate in the middle and apex; pinna apex obtuse to subacute. Veins visible on both sides of pinnae, dark brown at base of abaxial side of pinnae, lateral veins visible abaxially but obscure adaxially, forking and terminating in marginal teeth, only 1 or 2 basal basiscopic veins lacking. Sori linear, (2–) 4–6 mm long, medial, 8–15 on acroscopic side and 5–10 on distal basiscopic side of the pinnae in the middle part of the laminae, centers 1–3(–5) mm apart from one another; indusia brownish, linear, membranous, entire, the indusium of the second sorus on the acroscopic side of pinnae opening toward rachis or absent, other indusia opening toward costa.

Geographical distribution:— Hymenasplenium distans is currently only known from Hoa Binh and Thanh Hoa, northern Vietnam. It is likely endemic to Vietnam.

Ecology:— Hymenasplenium distans was observed to grow on wet rock in seasonal broad-leaved closed lowland forest.

Etymology:—The species epithet is based on the Latin adjective, distans , distant, referring to the relatively distant space on the rhizome between fronds of the new species.

Vernacular name:— ãďůďäffǎ (yuan ye mo ye tie jiao jue).

Taxonomic notes:— Hymenasplenium distans can be easily distinguished from other members of the H.unilaterale s.l. group by its quadrangular-trapeziform pinnae and long black stipe and 10 mm distance between neighboring fronds. The most similar species H. apogamum is widely distributed in Southeast Asia, while the new species is only found in North Vietnam. In our recent phylogeny H. distans formed a strongly supported clade with H. apogamum and H. ngheanense (described below).

Additional material examined:— VIETNAM. Thanh Hoa: Quan Hoa District, Phu Le Municipality, Hang village, 20°31’33”N, 105°05’06”E, elev. 350–500 m, seasonal broad-leaved closed lowland forest on very steep slopes of rocky ridge composed with crystalline marble-like highly eroded limestone, 30 September 2003, L. Averyanov, P. K. Loc, D. T. Doan & N. T. Vinh 3623 (MO!).

Figures

FIGURE 4. Hymenasplenium distans Li Bing Zhang, K.W. Xu & Liang Zhang.—A. Habitat and plants.—B. Rhizome.—C. Portion of abaxial lamina.—D. Basal pinnae of lamina.—E.Adaxial lamina.

FIGURE 5. Hymenasplenium distans Li Bing Zhang, K.W. Xu & Liang Zhang.—A. Habit.—B. Portion of adaxial lamina.—C. Portion of abaxial lamina.