Amanita bweyeyensis Fraiture, Raspe & Degreef

Fraiture, Andre, Amalfi, Mario, Raspe, Olivier, Kaya, Ertugrul, Akata, Ilgaz & Degreef, Jerome, 2019, Two new species of Amanitasect. Phalloideae from Africa, one of which is devoid of amatoxins and phallotoxins, MycoKeys 53, pp. 93-125 : 102-103

Amanita bweyeyensis Fraiture, Raspe & Degreef sp. nov. Figs 3, 4

Diagnosis.

Amanita bweyeyensis differs from the closest Amanita species by: pileus first pale brownish-grey then entirely whitish or with a faintly yellowish or pale beige shade, basal bulb of the stipe globose, neither pointed nor rooting, basidiospores subglobose to widely ellipsoid (Q = 1.10 –1.17– 1.28), absence of α- and β-amanitin, phalloidin and phallacidin in its basidiomata, connection with the genus Eucalyptus and distribution in Burundi, Rwanda and Tanzania.

Holotypus.

RWANDA. Western Prov.: buffer zone Nyungwe forest, Bweyeye (02°36.62'S; 29°14.04'E), ca. 2050 m alt., 16 Apr. 2015, J.Degreef 1304 (BR!).

Description.

Primordium subglobose, smooth, whitish or with a weak olive tint. Pileus 40 –73– 120 mm diam., first hemispherical then expanding to regularly convex or applanate, without umbo; margin even, not striate nor appendiculate, in some mature specimens the pileipellis does not reach the edge of the pileus, leaving free the extreme tip of the lamellae; first pale brownish-grey (close to 6B2 or 6C2-3), then often entirely whitish or with a faintly yellowish or pale beige shade (between 4A2 and 5B2); somewhat viscid, smooth, devoid of veil remnants. Lamellae free, white, becoming slightly yellowish when old and ochraceous, pinkish-beige to pale pinkish-brown on the exsiccates with a narrow white and fluffy edge; mixed with an equal number of lamellulae which are very variable in length and are usually truncated; sub-distant, 8-9 lamellae and lamellulae per cm at 1 cm from the edge of the pileus, about 120-160 lamellae and lamellulae in total (counts on 5 basidiomata), 3-14 mm broad, serrate when seen with a magnifying glass. Stipe 65 –95– 152 × 7-25 mm, ratio length of the stipe/diam. of pileus = 1.04 –1.25– 1.38; sub-cylindrical, slightly wider just under lamellae, gradually and slightly widened from top to bottom, white, with finely fibrillose surface, hollow (at least on exsiccates). Ring white, hanging, membranous but thin and fragile, finely fibrillose, smooth to somewhat plicate longitudinally, upper part adhering to the stipe and often more or less striate. Basal bulb of the stipe globose, sometimes a bit elongated but neither pointed nor rooting, up to 45 mm wide, surrounded by a white volva (also white inside), membranous, up to 30-35 mm high. Context white, soft; smell sweetish, conspicuous; taste not recorded.

Basidiospores hyaline, with thin, amyloid wall, (globose-) subglobose to widely ellipsoid (-ellipsoid), rather often with a mangiform or amygdaliform profile, (7.5-) 8.0 –8.81– 9.5 (-11.0) × (6.0-) 7.0 –7.54– 8.5 (-9.0) µm, Q = (1.00-) 1.10 –1.17– 1.28 (-1.58) [112/4/2]. Basidia 4-spored, without clamp, thin-walled, clavate, often rather abruptly swollen, 36 –42.3– 50 × (8.0-) 10.5 –12.0– 14 (-15) µm, l/w = 2.6 –3.59– 4.2 (-5.5) [66/4/2]. Lamellar edge sterile, composed of sphaeropedunculate marginal cells which are widely clavate to pyriform, hyaline, thin-walled, smooth, without clamp, 18 –26.3– 32 (-37) × 12 –17.0– 20 (-33) µm, l/w = (1.00-) 1.33 –1.57– 1.83 (-2.33) [40/4/2]. General veil (volva) mostly composed of cylindrical hyphae, with very different diameters, (15-) 35-80 (-110) × 2 –8.5– 15 (-26) µm, hyaline, with smooth and thin wall, septate, with rather frequent anastomoses between parallel hyphae, without clamps, branched, mixed with very few sphaerocysts, thin-walled, smooth, globose to ovoid, 33 –76– 125 × (25-) 32 –56– 95 µm, l/w = 1.00 –1.52– 2.25 [20/2/2].

Distribution.

At present, the species is only known from Burundi, Rwanda and Tanzania but, according to its ecology, it could probably be observed in all Eucalyptus plantations in tropical Africa and possibly in South Africa as well. Consequently, if the species is collected for consumption, care should be taken to avoid confusion with A. marmorata , a species growing in the same biotopes and suspected to be highly toxic.

Ecology.

On the ground, under Eucalyptus . The label of Saarimäki 591 indicates "in Acacia and Eucalyptus forest" whereas the legend of the associated picture ( Härkönen et al. 2003: 62) indicates "growing in an Acacia mearnsii plantation". However, the litter visible on that picture does not correspond to the latter species but looks like Eucalyptus leaves.

Etymology.

This species is named after the collection locality of the type specimen in Rwanda.

Specimens examined.

BURUNDI. Muravya Prov.: Bugarama, 9 Jan. 2011, J.Degreef 653 (BR). - RWANDA. Western Prov.: buffer zone Nyungwe forest, Bweyeye (02°36.79'S; 29°14.01'E), ca. 2040 m alt., 20 Oct. 2014, J.Degreef 1257 (BR); Ibidem (02°36.62'S; 29°14.04'E), ca. 2050 m alt., 16 Apr. 2015, J.Degreef 1304 (holotype: BR!). - TANZANIA. Pare District: South Pare Mts., Mpepera, ca. 1600 m alt., 5 Dec. 1990, T. Saarimäki et al. 591 (H).

Notes.

During collecting field trips in Rwanda, one of us (JD) was confused by observing local people (Abasangwabutaka) picking huge quantities of this mushroom in old Eucalyptus plantations and eating them (after removal of the cuticle) without experiencing any trouble. The species was not observed to be eaten in Burundi and is probably not used in Tanzania either.

It is quite likely that the specimen shown in a picture by van der Westhuizen and Eicker (1994: 38) under Amanita phalloides var. alba is Amanita bweyeyensis . This specimen was observed at Sabie (South Africa), growing in the leaf-litter under Eucalyptus cloeziana in early December and again in March. The pileus surface is described as "white and occasionally faintly yellowish over the central part" and the pileus margin as "very finely denticulate". Härkönen et al. (2003: 62) already drew attention to that picture.

A comparison with the closely related species is given in the chapter “discussion” below.