Diplazium cyamudongoense Eb.Fisch. & Lobin, 2023

Fischer, Eberhard & Lobin, Wolfram, 2023, Synoptic Revision of Diplazium (Athyriaceae) in Rwanda with description of Diplazium cyamudongoense sp. nov., Phytotaxa 600 (3), pp. 169-183 : 170-175

Diplazium cyamudongoense Eb.Fisch. & Lobin sp. nov. ( Figs. 1–3 , 4 A–D , 5 B–C ).

Type: — RWANDA. Western Province: Lacs Edouard et Kivu , Nyungwe National Park , Cyamudongo Forest , forest floor along stream, S2°32`26.89`` E28°59`20.46``, 1941 m, 18 September 2021, E. Fischer s.n. (holotype BR0000015253514V !; isotypes B 20 0220597! , B 20 0220598! , B 20 0220599! [frond on three sheets], KOBL!) .

Diagnosis: —The new species is morphologically similar to Diplazium nemorale ( Fig.5A ). Diplazium cyamudongoense sp. nov. has deeply incised to almost pinnate pinnules, all pinnae up to the terminal pinna are pinnatifid, there are 6–8(11) sori per pinnule lobe that are elongate, 1.98–2.95 mm long, and the base of stipe bears numerous large scales, which are more than 18 mm long. In D. nemorale the pinnules are shallowly to deeply cut, but the lamina does not appear tripinnate and is almost undivided towards pinna apex and on upper pinnae, the sori are 1–6 per pinnule lobe and 3–4(5) mm long, the scales at stipes base are not exceeding 9 mm in length.

Description: —Terrestrial fern. Rhizome erect, scaly; scales very large, dark brown, of two types, long filiform, extremely fragile, thus almost all broken, larger scales with broad base, more than 18.38 mm long, at base 1.95 mm, further upwards 0.97 mm, at the tip 0.54 mm wide, smaller scales linear, more than 15.3 mm long, at base 0.74 mm, further upwards 0.38 mm and at tip 0.08 mm wide. Fronds tufted. Stipes light green, at base dark brown, canaliculate, 40–47(–108) × 0.7 cm, base with scales similar to those from rhizome. Lamina 59–69(–105) × 47.5–64 cm, triangular– ovate, green, shiny on upper surface, 2–pinnate–pinnatifid to nearly 3–pinnate. Rachis greenish–brown to middle– brown, with few scales. Pinnae in ca. 15–18 pairs, alternate, arranged at an angle of ca. 45°, (15.3–)23.7–34 × 14.5–17 cm; pinnae rachis light–brown to greenish, base often darker, with few scales, sometimes minutely hairy. Pinnules in 12–14(–19) pairs in each pinna, opposite, (4.5–)5.1–6.6(–9.2) × 1.6–2.3(–4.5) cm, oblong–lanceolate. Pinnules 3 rd order in 6–10(–12) pairs tapering into the caudate apex, opposite, 0.9–1.1 × 0.4–0.6 cm, decurrent, deeply incised; racheolule mostly winged. Sori elongate, 1.98–2.95 × 0.71–0.98 mm, in basic pinnule lobes up to 6 sori, in all other sori usually in two rows along midrib, 6–8(11), paraphyses present, 237–350 µm long, sometimes with short branches. Indusium elongate, pale, glabrous, same size as sori attached to one side of sorus (asplenioid). Sori 6–11 per pinnule. Spores with alate perispore, 42–50.5 × 25.7–31.46 µm, alae curved and narrow, 4.29–7.15 µm high and 1.14–1.43 µm wide, the remaining perispore smooth with small folds.

Additional specimens seen (Paratype):— RWANDA. Western Province: Lacs Edouard et Kivu , Nyungwe National Park , Cyamudongo Forest , forest floor along stream Nyamabuye , 1877 m, S2°33`17.42`` E28°59`03.56``, 16 March 2022, E. Fischer, P. Ballings & B. Wursten s.n. ( KOBL).

Distribution: — Rwanda ( Cyamudongo Forest ).

Habitat: — Montane forest along streams, elev. 1877–1941 m.

Etymology: — The species name refers to the Cyamudongo Forest, a place of extreme high diversity in animals and plants. Until now, the new species is only known from two localities in this exciting area.

Conservation status: —With only two collecting sites, it is not possible to calculate an Extent of Occurrence (EOO). EOO: not applicable; AOO: 18 km 2. The area of occupancy (AOO) falls within the limits for the Critically Endangered category. However, as the species occurs within a well-protected area, only in protected areas and therefore to experience no threat or decline, it cannot be assessed in any threat category; Therefore, it should be assessed as Least Concern (Protected area dependent).

Figures

FIGURE 1. Diplazium cyamudongoense Eb.Fisch. & Lobin sp. nov.—A, B. Fronds.—C, D. Pinnules. Photographs: E.Fischer, Cyamudongo. Scale bars: A, B. 10 cm; C, D. 1 cm.

FIGURE 2. Diplazium cyamudongoense Eb.Fisch.& Lobin sp. nov.—A, B. Detail of fronds.—C.Base of stipes with scales.—D. Pinnules. Photographs: E.Fischer, Cyamudongo. Scale bars: A. 5 cm; B, D. 2 cm; C. 1 cm.

FIGURE 3. Diplazium cyamudongoense Eb.Fisch. & Lobin sp. nov.—A, B. Base of stipes with scales.—C–E. Fragments of brittle scales.—F, G. Detail of pinnules showing sori. Photographs: E.Fischer & W.Lobin, Cyamudongo. Scale bars; A, B, G. 1 mm; C, D, E. 2 mm; F. 3 mm; G. 1 mm.

FIGURE 4. Diplazium cyamudongoense Eb.Fisch. & Lobin sp. nov.—A–D. Spores.— Diplazium humbertii —E–F. Spores. Photographs: E.Fischer, W.Lobin & Y.Malkowsky, A–D. Cyamudongo; E–F. Cyamudongo. Scale bars: A, B, C, E, F. 10 µm; D. 8 µm.

FIGURE 5. Diplazium nemorale.—A. Pinnules.—Diplazium cyamudongoense Eb.Fisch.&Lobin sp.nov.—B–C.Pinnules.Photographs: E.Fischer, A. Pócs & Chambuko 6223; B–C. E.Fischer s.n. Scale bars: A, C. 3 mm; B. 5 mm.A reproduced with permission from BR.