Isoetes pichisermollii Eb. Fisch. & Lobin, 2022

Fischer, Eberhard & Lobin, Wolfram, 2022, The genus Isoetes (Isoetaceae) in Central Africa (Democratic Republic of the Congo, Rwanda, Burundi) with the description of three new species, Willdenowia 52 (3), pp. 315-334 : 330-331

Isoetes pichisermollii Eb. Fisch. & Lobin , sp. nov. – Fig. 10–11, 14B.

Holotype: Burundi, Bubanza district, Rusizi plain, km 14, 800 m, temporary swamp, 16 Mar 1975, Reekmans 4400 ( K001291890 ).

Diagnosis — The new species differs from Isoetes abyssinica in the much longer leaves (240–460 mm vs 114– 188 mm) and in the megaspore micromorphology. The megaspores are smaller (c. 400 × 400 µm vs c. 480 × proximal face trilete, bearing spaced tubercles 7–11 per areole, 11.25–22.5 µm in diam., with dense threads in between, only a small apex free of waxes, ridges c. 50 µm wide and c. 20 µm high, almost free of waxes; distal face with spaced larger and smaller pustules, 30–45 µm in diam., partly anastomosing, c. 26.25 × 15 µm, with dense threads between pustules, large apex of pustules free of waxes. Microspores not seen.

Distribution — Known only from the type locality in the Rusizi plain of W Burundi (Fig. 14 B). The above cited collections were already mentioned as Isoetes abyssinica Chiov. by Pichi Sermolli (1983, 1985).

Habitat — Amphibious, in seasonally waterlogged depressions in palm savanna, 780–850 m.

IUCN conservation assessment (preliminary) — Critically Endangered: CR

B2ab(iii). Isoetes pichisermollii is known only from the type locality and its immediate surroundings. The last collections were made c. 50 years ago. The estimated AOO is

4 km ² (assuming a 4 km ² grid cell size). The habitat, a seasonally waterlogged depres-

sion in palm savanna, is under high pressure by agriculture (see Ntore & al. 2018). Because a part of the Rusizi plain is situated in eastern D. R. Congo, the species may well also occur in that country. Fig. 14. A: distribution map of Isoetes hallei (black circle). – B: distribution map of I. rwandensis (yellow circles) and I. pichisermollii (red circles). – Red

Etymology — Named after Rodolfo Emilio lines indicate country borders, blue lines and surfaces rivers and lakes. – Scale bars: A = 1500 km; B = 100 km. Guiseppe Pichi Sermolli (1912–2005), a famous Italian pteridologist, who first mentioned the taxon from Burundi. 460–480 µm in I. abyssinica ). The distal face in the new species has spaced larger and smaller pustules, where- Taxonomic notes — Verdcourt (2005: 3) stated, withas in I. abyssinica the distal face is clavate with distant out having seen the spores, that “these Burundi speciprojections and small tubercles in between. The new mens [of Isoetes abyssinica ] seem too robust”. Isoetes species also differs from I. schweinfurthii , which has a abyssinica s.str. was placed into synonymy of I. welsimilar leaf length, in the megaspore micromorphology. witschii by Verdcourt (2005), but there are sufficient dif- The megaspores are smaller (c. 400 × 400 µm vs (360–) ferences, e.g. in megaspore micromorphology, to keep 440–520 × (360–)440–525 µm in I. schweinfurthii ). The both taxa as separate species. The specimen Reekmans proximal face bears spaced tubercles 7–11 per trilete sur- 4400, which we have chosen as the holotype, bears a face, whereas in I. schweinfurthii it is laevigate or bears pencil annotation by Henk Beentje who identified it as 3 tubercles at most. I. schweinfurthii .

Description — Corm 3-lobed, 10–20 mm wide, bud scales c. 9 × 4 mm, cuspidate, blackish. Leaves (6–)10 or 11, 240–400(–460) mm long, 4–5 mm wide at base, c. 1 mm wide at apex, tapering gradually to a slender apex. Ligule not seen. Velum absent. Megasporangia c. 5 × 3 mm, sporangial wall pale. Megaspores c. 400 × 400 µm;

Additional specimens studied — BURUNDI: BUJUM- BURA: vallée Mugegi , km 14, 13 Mar 1971, Reekmans 91 ( BR0000015460400 ) . — BUBANZA: plaine de la Rusizi, 19 Feb 1971, Lewalle 5192 ( BR0000013164775 ) ; plaine Rusizi km 14, 18 May 1974, Reekmans 3451 ( BR0000015460424 , K001291891 ) .