Pilularia ethiopica Eb.Fisch., Killmann, Mark.Ackermann & Kumelachew Yeshitela, 2023

Fischer, Eberhard, Killmann, Dorothee, Ackermann, Markus & Yeshitela, Kumelachew, 2023, Pilularia ethiopica (Pteridophyta, Marsileaceae), a new species of pillwort from the tropical African mountains of Ethiopia, Phytotaxa 612 (1), pp. 77-86 : 78-85

Pilularia ethiopica Eb.Fisch., Killmann, Mark.Ackermann & Kumelachew Yeshitela , sp. nov. ( Figs 1–5 )

Type: — ETHIOPIA. Bale Mountains National Park , growing on sand and partly covered by water in small Afroalpine pond, open Helichrysum heath with many tufted grasses, around the numerous small lakes of the area, 6 November 1988, I . Friis, A. Michelsen & Sebsebe Demissew 5727 (holotype ETH; isotype C) .

Diagnosis: — Pilularia ethiopica is similar to P. americana , P. bokkeveldensis , and P. dracomontana . It differs from both P. americana and P. bokkeveldensis in the smaller sporocarp, shorter pedicel and sporocarps that are subterranean at maturity, and from both P. bokkeveldensis and P. dracomontana in the obvious circinate vernation. It also differs from P. americana in the shorter fronds and from P. dracomontana in the longer fronds, longer pedicel, and permanently submerged habit of that species. Pilularia ethiopica is found in Afroalpine tarns above 3 460 m, while P. bokkeveldensis occurs in seasonal pans at 800 m and P. dracomontana in perennial sandstone tarns at 2 130–2 160 m. Additionally P. americana may have more than one leaf per node ( Correll 1956), while P. ethiopica , P. bokkeveldensis , and P. dracomontana always bear only one leaf per node.

Description: —Plants aquatic, partly submerged, mat-forming. Rhizome filiform, creeping, irregularly branched, up to 0.4–0.5 mm in diam., with 2(–3) roots at nodes, internodes 2.5–5.0(–11.0) mm long. Fronds borne singly at nodes, erect, simple, setiform, flexuose, 13–30(–45) mm long, 0.4–0.5 mm in diam., circinate vernation obvious. Sporocarp subterranean, globose, 1.8–2.1 mm in diam., yellowish to cream-coloured, sparsely hairy, hairs up to 3–4 cells and c. 100 µm long, appressed; sporocarps 4–locular, each locule with single sorus containing micro- and megasporangia, sporocarp pedicel arising from node on rhizome, up to 0.5–1.0 × 0.2–0.3 mm, produced laterally, bent downwards. Microsporangia clavate, several per sorus. Microspores 46–51 µm in diam. Megasporangia ellipsoid, 0.6–0.8 mm in diam. Megaspores 170–171 µm in diam.

Distribution: — Pilularia ethiopica is endemic to the southern highlands of Ethiopia within the Bale Mountains and one record about 150 km west of Bale.

Habitat: —The new species occurs at the margin of perennial tarns in Afroalpine grassland above 3 460 m. It is probably completely submerged in the rainy season and becomes partly exposed in the dry season. Mature sporocarps were observed in March and November. Of all genus members P. ethiopica probably occurs at the highest altitude (except the Southern American P. americana that was recorded in Peru between 4 530 and 4 593 m; Léon et al. 2018).

Discussion: — Pilularia ethiopica has been misidentified as P. americana with which it shares the 4-locular sporocarps. It differs, however, in the shorter fronds [13–30(–45) mm vs. 20–90 mm], the smaller sporocarp (1.8– 2.1 mm in diam. vs. 2.0– 2.5 mm in diam.), the shorter pedicel (0.5–1.0 mm vs. 2.0– 3.7 mm), and the subterranean sporocarps at maturity. The latter feature is almost unique, only recorded hitherto in P. dracomontana . Pilularia ethiopica differs from the two other African species, P. bokkeveldensis and P. dracomontana , in the obvious circinate vernation that is usually not observable in the latter taxa ( Table 1 ). It differs from P. bokkeveldensis in the smaller sporocarps, the shorter pedicel, and the subterranean sporocarps at maturity. Pilularia bokkeveldensis has sporocarps that grow downwards but that are epigeal at maturity. It differs from P. dracomontana in the longer fronds, the longer pedicel, and the only partly submerged habit. Pilularia ethiopica is found in Afroalpine tarns above 3 460 m, while P. bokkeveldensis is an annual that occurs in seasonal pans at 800 m, and probably survives the dry season with its sporocarps, and P. dracomontana grows in perennial sandstone tarns at 2 130–2 160 m as a permanently submerged perennial (or perhaps annual as it is not yet known whether the plants persist through the freezing winter months). For descriptions of P. bokkeveldensi s and P. dracomontana see Crouch et al. (2011) and Crouch & Wesley-Smith (2011).

Additional specimens examined (paratypes):— ETHIOPIA. Bale Mountains National Park , pond below Fincha Habera Waterfalls SW of Dinsho, N07°00’58.77” E39°43’18.80” 3 462 m, 2 March 2005, Kumelachew Yeshitela s.n, ( ETH); 64 km along road to Hosanna (= Hosaena), 4 November 1972, J. W . Ash 1753 ( K) .

Figures

FIGURE 1. Pilularia ethiopica. Photograph of the isotype at C. Reproduced with permission.

FIGURE 2. Pilularia ethiopica. A. Habitat, Bale Mountains, pond below Fincha Habera Waterfalls SW of Dinsho. B & C. Habit (Photographs E. Fischer). Scale bars: B. 5 mm, C. 1 mm.

FIGURE 3. Pilularia ethiopica. A–C. Habit (Photographs E. Fischer). Scale bars: A. 5 mm, B. 1 mm, C. 5 mm, arrow showing circinate vernation of frond.

FIGURE 4. Pilularia ethiopica. A & B. Detail of habit showing immature sporocarps. C. Sporocarp, tangential section of an immature sporocarp (Photographs E. Fischer).

FIGURE 5. Distribution map of Pilularia globulifera, P. minuta, P. ethiopica, P. bokkeveldensis, and P. dracomontana. After Fomin (1934), Bobrov (1974), Dostál & Reichstein (1984), Dubina & Czorna (2009), Crouch et al. (2011), Christenhusz et al. (2017), and Minissale et al. (2017).