Hymenasplenium hovenkampii K.W.Xu & Li Bing Zhang, 2023

Xu, Ke-Wang, Liu, Yu-Xuan, Chen, Yi-Fei & Zhang, Li-Bing, 2023, Hymenasplenium hovenkampii (Aspleniaceae), a new bipinnatisect fern species from Lesser Sunda Islands of Indonesia, Phytotaxa 595 (1), pp. 120-124 : 120-122

Hymenasplenium hovenkampii K.W.Xu & Li Bing Zhang , sp. nov. ( Figure 1 ).

Diagnosis:—This new species is morphologically similar to Hymenasplenium cheilosorum (Kunze ex Mettenius 1859: 133) Tagawa (1938: 84) and H. sabahense Li Bing Zhang, K.W.Xu & C.W.Chen in Xu et al. (2019: 38) in having sori terminal on subtending veins and situated in pinna lobes, but the former has laminae bipinnatisect, rachises reddish brown, and the acroscopic margins deeply lobed and usually with 4–5 lobes and each lobe deeply or shallowly crenate to dentate with two teeth, while both the latter two species have laminae 1-pinnate, rachises dark purplish to black, and the acroscopic margins relatively shallowly lobed with more than 5 lobes and each lobe shallowly crenate to dentate with two teeth ( Table 1 ).

Type:— INDONESIA. East Nusa Tenggara: Lesser Sunda Islands, Manggarai, Ruteng, 18 April 1983, Schmutz E 5646 (holotype: L-3507947!) .

Plants perennial, evergreen, 25–35 cm tall. Rhizomes long creeping, ca. 2 mm in diameter, apex scaly, scales brown, those narrowly triangular or lanceolate with entire margins; root yellowish brown when dried, slender, rhizome and root usually covered with yellow brown floccose indument. Fronds remote, membranous-herbaceous; petioles slender, shiny, reddish brown, glabrous, 4–10 cm long, ca. 1 mm in diameter. Laminae narrowly lanceolate, bipinnatisect, 14– 20 × (1.5–)2–2.5(–3) cm, base reduced, widest near base, gradually narrowing toward apex, apex acuminate; rachises 0.5–1 mm in diameter, glabrous, shiny, reddish brown, adaxial side grooved and with 2 green narrow wings. Pinnae shortly stalked to almost sessile at apex, 30–40 pairs, base nearly opposite, middle and apex alternate, rectangular to trapeziform, (middle pairs) (1–)1.2–1.8(–2.5) × 0.4–0.5 cm, 1–4 mm apart, base asymmetrical, acroscopic side truncate and subparallel with rachis, basiscopic side cuneate, acroscopic margins deeply lobed, usually with 4–5 lobes, each lobe usually deeply or shallowly crenate to dentate with two teeth, teeth obtuse or sometimes acute, entire, basiscopic margins entire at base, lobed at the apex; pinna apex obtuse to acute, lower pinnae deflexed or spreading, upper pinnae ascending. Veins visible on both side of pinnae, green, forking and terminating in marginal teeth, 1 vein per marginal tooth and ending below tooth, usually 3–4 or rarely all basal basiscopic veins lacking. Sori elliptic to linear, 1.5–2 mm long, at tip of subtending veins and located in or below marginal teeth; indusia brown, linear, membranous, entire.

Habitat and distribution:— Hymenasplenium hovenkampii was observed to grow in shaded and wet places along streams in forests at an elevation of ca. 1300 m. This species is currently only known from Ruteng of Lesser Sunda Islands. It is likely endemic to Indonesia .

Etymology:—In honor of the late Professor Peter Hovenkamp based at L for his contributions to pteridology and Flora Malesiana in particular.

Notes:— Hymenasplenium hovenkampii is obviously a member of the H. cheilosorum group based on its sori terminal on subtending veins and situated in or below ultimate segments of pinnae ( Figure 2 , Xu et al. 2018, 2019a). This species is the only species with bipinnatisect laminae in Hymenasplenium . Up to now, three species, H. cheilosorum , H. inthanonense N.Murakami & J.Yokoyama in Iwatsuki et al. (1998: 43), and H. sabahense have been recorded in the H. cheilosorum group. The pinnae of the three species are deeply or shallowly lobed. Among them, the pinnae of H. sabahense are deeply lobed to half of the pinna width, H. cheilosorum lobed up to 2/5 of the pinna width, and H. inthanonense only shallowly lobed. However, the pinnae of H. hovenkampii are lobed to the costa, forming a bipinnatisect laminae. This is very different from other members in the genus. In addition, the acroscopic margins of the new species are deeply lobed and usually with 4–5 lobes and each lobe is deeply or shallowly crenate to dentate with two teeth, while the acroscopic margins of the other three species in the H. cheilosorum group are relatively shallowly lobed and with more than 5 lobes and each lobe is usually shallowly crenate to dentate with two teeth ( Table 1 ).

Selected specimen examined (Paratype):— INDONESIA. East Nusa Tenggara: Lesser Sunda Islands, Manggarai, Ruteng , 1300 m, 20 May 1982, Schmutz E 5352 (L-3507945!) .

Figures

FIGURE 1. Hymenasplenium hovenkampii sp. nov.—A. Holotype.—B. Middle portion of lamina (Drawn by Ke-Wang Xu based on the type).

FIGURE 2. Hymenasplenium hovenkampii sp. nov.—A. Enlarged portion of laminae (some sori distributed in the pinnae are indicated by white arrows).—B. Fronds showing that the pinnae are lobed to the costa.