The following information is almost entirely based on the original description of Beeli. Gilbert (1940) provides one spore drawing and an hypothesis concerning the present species' possible being based on an old specimen of A. strobilaceovolvata (see discussion, below).
The viscid, bell-shaped or broadly bell-shaped cap of A. fibrillosa is about 70 mm wide, brown-sepia, and darker over the marginal striations and over a central umbo. The soft flesh becomes slightly pinkish upon exposure to air. The cap's margin is striate. It bears rather easily crumbling warts in the shape of pyramids.
The free gills are white with a brown edge and about 6 mm broad. Beeli states that the gills number 9 per cm [possibly as measured along the cap's circumference]; and the short gills, 3 per cm.
The solid, ringless stipe is 120 - 130 × 6 - 8 mm, whitish, cylindric, and covered with grayish fibrils. The flesh becomes slightly pinkih on exposure to air. The volva is saccate, membranous, and ochraceous and has its surface divided into slightly bulbous regions.
The odor of this species is said to be agreeable; and the taste, sweet with a sharp aftertaste.
Two authors [Beeli (1935) and Gilbert (1940)] have reported on the spores of this species. Their data is incompatible. The data drived from Gilbert' spore drawings has been shown to be more reliable in other cases; hence, the spores are about 9.6 - 11.7 × 8.1 - 9.6 μm, broadly ellipsoid, and inamyloid.
This species was originally described from the Democratic Republic of Congo. It was described as occurring singly in dry forest.
Gilbert proposed that the present species is based on an old specimen of A. strobilaceovolvata that had lost is ring and (presumably) become decolored. This seems unlikely. It would be unusual for a post-mature specimen of an Amanita to have larger spores than are found in a younger specimen of the same species.
["fibrilosa" (sic)] Beeli. 1935. Fl. Iconogr. Champ. Congo 1: 22, tab. 4 (fig. 1). [Note: Correct spelling of the epithet appears in the caption to the figure.—ed.]
fibrillosus "covered with fine (thread-like) fibers"
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The following material is derived from the protolog of the present taxon and (Gilbert 1940 & 1941).
from protolog: 70 mm wide, brown-sepia darker over striations and umbo, expanded-campanulate, umbonate, slightly viscous; context soft fleshy, fibrillose, becoming slightly pink on exposure to air; margin striate (ca. 0.2-0.3R per figure); universal veil as several warts, pyramidal, flocculent.
from protolog: free, 9 per cm, white, with brown edge, 6 mm broad, acute at both ends, thin; lamellulae 3 per cm.
from protolog: 120 - 130 × 6 - 8 mm, whitish, cylindric, covered with grayish fibrils; context solid, soft, fibrillose, becoming slightly pink on exposure to air; exannulate; universal veil as saccate volva, membranous, ochraceous, with surface divided into slightly bulbous regions.
from protolog: Odor agreeable. Taste of walnuts with a sharp aftertaste.
from protolog: 6 - 7 μm, hyaline, smooth, "globose"; apiculus present (per figure); contents guttulate; white in deposit. [Note: According to the drawing by Mme. Goossens, the spores are subglobose or broadly ellipsoid; however, they are not presented in lateral view. Data is insufficient for generation of a sporograph.—ed.]
Gilbert (1940): [2/1/1] 9.6 - 11.7 × 8.1 - 9.6 μm, (Q = 1.19 - 1.21), broadly ellipsoid, inamyloid. [Note: Spore measurements are taken from the two drawings of (Gilbert 1940: tab. VI (fig. 2)) that are even close to being presented in lateral view. As it is, the spore's widths are probably exaggerated and the length of the larger one reduced by the apparent orientation of the spore; consequently, the Q values are suppressed.—ed.]
from protolog: Solitary. Terrestrial in dry forest.
from protolog: CONGO, DEMOCRATIC REPUBLIC OF: PROV. EQUATEUR—Territoire Lisala - Binga [2°23'41" N/ 20°25'25" E, 361 m], ii.1932 M. Goossens-Fontana 960 (holotype, BR, watercolor).
Gilbert (1941) treated this species as based on an old specimen of A. strobilaceovolvata Beeli. However, it would be very odd for the spores of an old speciment to be larger and narrower than those of a young one; and this is the case if one compares the few spores drawn by Gilbert from the implicit holotypes of the two species in question [Gilbert 1941: 93, tab. VI (figs. 1 and 2)]. The sample size is minimal; however, the following figure provides comparisons of the sporographs of the present species and A. strobilaceovolvata.
there are pyramidal warts on the cap of the present species while the cap of A. strobilaceovolvata is glabrous;
the marginal striations of the present species are proportionately half the length of those in A. strobilaceovolvata
the volva at the stipe base of A. fibrillosa is thin and clings to an irregularly formed stipe base, while the thick and fleshy volva of A. strobilaceovolata has a substantial orangish-brownish cross-section (per figure) that encloses the base of a totally elongating stipe
the cap of the present species has a low, broad umbo, while the umbo in A. strobilaceovolvata is proportionately narrower and more pronounced.
—R. E. Tulloss
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Spore data for collections provisionally identified as: Amanita fibrillosa Beeli
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