Ripartitella degreefii Rizinde, Desjardin, Amalfi, & Decock 2023, sp. nov.
Creators: name: Hakizimana, Jean-Claude Rizinde
name: Amalfi, Mario
name: Degreef, Jérôme
name: Desjardin, Dennis
name: Decock, Cony
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Fungi
Basidiomycota
Agaricomycetes
Agaricales
Agaricaceae
Ripartitella
Ripartitella degreefii

description: Ripartitella degreefii Rizinde, Desjardin, Amalfi, & Decock, sp. nov. Figs. 2, 3
[Mycobank: MB842786]
Diagnosis:—The species is similar to R. brasiliensis in the basidioma habit, but differs in the paucity of pleurocystidia, a pileipellis as a cutis, and its habitat in mountain areas of tropical Africa.
Description:— Basidiomata cespitose, small to medium-sized (Fig. 2A, B). Pileus 25–70 mm diam., convex to planoconvex, becoming applanate and depressed, with (or without) a small obtuse umbo; surface dull, dry, pure white to off-white, disc with (or without) tiny, brownish orange (ferruginous 7C6–7]) scales when young, wearing off with age. Margin decurved to sometimes uplifted in age, centrally pure white to cream (4A3) with white appendiculate veil remnants. Context 1–2 mm thick, soft, white. Lamellae shallowly adnexed to adnate, crowded to very crowded, unequal, (24 (L+l) / cm), with 2–4 series of lamellulae, narrow (2–3 mm deep), with smooth edge, pale yellowish white (4A2). Stipe central to slightly eccentric, terete, subclavate to bulbous, 15–70 (–100) mm long, 3–10 mm broad, solid, annulate, concolorous with pileus, squarrose, with superficial, scattered white velar remnants toward base, glabrous above the annulus. Annulus evanescent, single, membranous, felted, often incomplete, attached to the upper quarter of the stipe. Odor fungoid, taste not tested. Spore print white Hyphal system monomitic, composed of generative hyphae with clamp connections in all tissues. Pileipellis a cutis, made up of repent, subparallel, radially oriented, cylindric hyphae, 3.5 – 7 µm diam, smooth, thin-walled. Pileus squamules composed of subcatenulate, rarely encrusted hyphae, 5 – 10 µm diam. Pileitrama made up of interwoven hyaline, smooth, thin- to slightly thick-walled, hyphae, 2.5–7 µm diam. Lamellar trama similar to pileitrama. Stipitipellis a layer of ±parallel, longitudinally oriented hyphae, with scattered clusters of subcatenulate elements similar to those of pileipellis (Fig. 3C), individual cells 3.5 – 7 µm diam, smooth, thin-walled.
Basidiospores hyaline (Fig. 3G, H), broadly ellipsoid to subglobose, thin-walled, verrucose, inamyloid, acyanophilous, (3.5–) 4–5 × 3–3.8 µm (n = 30, mean = 4.3 × 3.4 µm, Q = 1.13–1.5). Basidia with a basal clamp, clavate, with 4 sterigmata (Fig. 3F), not siderophilous, 14–24 × 6–8 µm. Pleurocystidia absent or present (Fig. 3D), then scarce, difficult to observe, with a basal clamp, lageniform, thin- to thick-walled, apically smooth or slightly, finely or coarsely incrusted (Fig. 3E), 32–40 × 5.0–7.5 µm, the apical digitate part 2–2.5 µm diam (mean =36 × 6.5 µm, 2.3 µm in the apical section). Cheilocystidia not observed.
Distribution:—AFRICA. Known from the Eastern Democratic Republic of the Congo and S„o Tomé.
Ecology (substrate, host, habitat):— On fallen trunks of angiosperms, including, in DRC, Xymalos monospora (Harv.) Baill. (Monimiaceae, locally named “Cinyalubombo”), mountain forests, at 1100 and 2139 m a.s.l.
Etymology:—The species name is a tribute to Jérôme Degreef, scientific director at Meise Botanic Garden for his devotion to African mycology and his efforts for promoting the training of students from tropical Africa.
Material examined:—AFRICA. Democratic Republic of the Congo, South Kivu: Kahuzi Biega mountain range, Kahuzi Biega National Park, 2.331733°S, 28.74848°W, 2139 m a.s.l., on fallen trunk of Xymalos monospora (Harv.) Baill. (Monimiaceae), November 2018, J.C. Rizinde leg., RHJ 305 (BR #5020189043549, Holotype), culture exholotype MUCL 57374; SÃO TOMÉ: Macambrara radio antenna area; 0.27595°N, 6.608767°E, 1100 m elev., 25 April 2008, D. E. Desjardin leg. DED 8323; SÃO TOMÉ; Macambrara radio antenna area; 0.27595°N, 6.608767°E; 1100 m elev., April 2006, D. E. Desjardin leg., DED 7937 (but material lost in transit to the USA).
Notes:— Ripartitella degreefii is phylogenetically distant from all other Ripartitella known to date (Fig. 1). Morphologically, R. degreefii is similar in many respects to R. brasiliensis (Capelari & Asai 2009, Desjardin & Perry 2017), but differs in having a pileipellis as a cutis (Fig. 3C) as opposed to a trichoderm (Capelari & Asai 2009), scarce (Fig. 3D–E) in contrast to abundant pleurocystidia (Capelari & Asai 2009), and a distribution in Afromontane forests in contrast to lowland neotropics. Ripartitella brasiliensis also has dense, brown to reddish brown squamules, covering the whole cap when young (Capelari & Asai 2009, Battistin et al. 2016). Squamules are variably present in young specimens of R. degreefii (Fig. 2), but soon wear off with age.
Ripartitella degreefii is known so far from two collections originating from two spots of medium elevation forests, in the continental and insular Afromontane range, in the Albertine rift (DRC) and S„o Tomé. It is the first Ripartitella described from Tropical Africa. Pegler (1977) reported R. brasiliensis from Eastern Africa, in Kenya, Tanzania, and Uganda. He described the eastern African collections as lacking cystidia (Pegler 1977). Pleurocystidia were observed in R. degreefii, in both specimens available. However, they are scarce and difficult to see. Desjardin and Perry (2017) reported R. degreefii under R. brasiliensis from S„o Tomé, stating that it matched “nicely the description of African material provided by Pegler (1977) ”. A closer examination of the S„o Tomé specimen revealed the presence of scarce pleurocystidia. The identity of the specimens cited by Pegler (1977) remains to be ascertained but they could represent R. degreefii.
description: Published as part of Hakizimana, Jean-Claude Rizinde, Amalfi, Mario, Degreef, Jérôme, Desjardin, Dennis & Decock, Cony, 2023, Ripartitella degreefii (Tricholomataceae), a new species from tropical Africa, pp. 195-207 in Phytotaxa 597 (3) on pages 202-204, DOI: 10.11646/phytotaxa.597.3.1, http://zenodo.org/record/7958574