The orange to brownish orange then reddish yellow cap of Amanita rubromarginata measures up to 80 mm wide and has a long sulcate-striate margin. The cap is at first cylindric-campanulate then expands to nearly plane to slightly concave and subumbonate. It is glabrous and subviscid when wet. The flesh is soft, 3 - 7 mm thick in the center, yellowish white, and deeper yellow below the cap skin.
The gills are free, very close (55 - 70 reach the stipe), pale yellow and have reddish orange edges. Short gills are of diverse lengths.
The stem is 60 - 120 × 5 - 16 mm, yellow, and has a thin, membranous, reddish orange annulus and and a thick, white, saccate volva. The stem is subcylindrical or slightly tapering upward, hollow, silky fibrillose, and appressed with indefinite, orange-red squamules forming irregular transverse zones.
The spores measure 8 - 9 × 5.5 - 7 μm and are broadly ellipsoid to ellipsoid and inamyloid. [Note: RET spore measurements from an isotype specimen are 7.5 - 9.5 (-10.5) × (5.8-) 5.9 - 6.9 (-7.6) μm, with spores dominantly ellipsoid, sometimes broadly ellipsoid, and rarely elongate.] Clamps are present at bases of basidia.
Amanita rubromarginata is easily distinguished from Amanita hemibapha (Berk. & Broome) Sacc. var. hemibapha [Ed. Note: In the present article, this must be taken sensu auct. japon.], Amanita hemibapha var.ochracea Zhu L.Yang, and Amanita javanica (Corner & Bas) T. Oda, C. Tanaka, & Tsuda by its smaller fruiting body, and its reddish orange annulus and reddish marginate gills. [Ed. Note: Amanita rubromarginata is assignable to Amanita stirps Hemibapha, in the small-spored group (see key). The spores of the present species are more narrrow than those of A. hemibapha sensu auct. japon. (=A. caesareoides Lyu. N. Vassilieva), the cap of which is brilliant red. While A. hemibapha var. ochracea and A. javanica are similar to the present species in cap color, they both have larger spores and can be easily distinguished using the key on this site.]
Amanita rubromarginata was described from Oak-Chinkapin forests on Ishigaki Island (Okinawa, southwestern Japan).—Dr. H. Takahashi
S. Sanchez et al., (direct deposit), Roy. Ontario Mus., Toronto
KPM [Kanagawa Prefectural Museum of Natural History]; isotype, RET
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The following material is from the protolog and from original research of R. E. Tulloss.
from protolog: 40 - 80 mm wide, at first orange (6B7-8) to brownish orange (6-7C7-8) overall, then reddish-yellow (4B7-8) toward margin, in age grayish yellow (4C7) over disc, at first cylindric-campanulate, expanding to nearly planar to slightly concave and subumbonate. glabrous, subviscid when wet; context soft, yellowish white except deeper yellow just below pileipellis, 3-7 mm thick over stipe; margin long sulcate-striate; universal veil absent.
from protolog: free, very close (55 - 70), pale yellow, up to 10 mm broad, with edges fimbriate and reddish orange (7B7-8); lamellulae in 1-3 "series."
from protolog: 60 - 120 × 5 - 16 μm, pale yellow, usually covered with reddish orange (7B7-8) appressed "indefinite squamules forming irregular transverse zones," subcylindric or slightly narrowing upward, silky fibrillose; context hollow; partial veil subapical, thin, membranous, 10-15 mm wide, reddish orange (7B7-8), striate [above]; universal veil as saccate volva, 20 - 40 × 10 - 25 mm, thick, bilobate, white, sometimes stained dingy brown.
from protolog: Odor and taste indistinct.
from protolog: filamentous hyphae 4 - 8 μm wide, with orange (5A6) to deep orange (5A8) intracellular pigment, thin-walled; clamps occasional.
from protolog: [20/2/2] 8 - 9 × 5.5 - 7 μm, (Q = 1.28 - 1.45), colorless, smooth, thin-walled, inamyloid, broadly ellipsoid to ellipsoid; apiculus sublateral and truncate-conic (both per figure); contents as large refractive guttule; color in deposit not recorded.
from isotype in RET: [21/1/1] 7.5 - 9.5 (-10.5) × (5.8-) 5.9 - 6.9 (-7.6) μm, (L = 8.5 μm; W = 6.3 μm; Q = (1.21-) 1.22 - 1.43 (-1.69); Q = 1.34), hyaline, colorless, smooth, thin-walled, broadly ellipsoid to ellipsoid (infrequently elongate), often adaxially flattened; apiculus ??; content dominantly monoguttulate with occasional small granules; color in deposit not recorded.
from protolog: Scattered. In broad-leaved forest dominated by Quercus miyagii Koidz. and Castanopsis cuspidata (Thunb. ex Murray) Schottky var. sieboldii (Mak.) Nakai..
from protolog: JAPAN: OKINAWA-KEN—Ishigaki Isl., Ishigaki-shi, Banna-dake, 8.vi.2001 H. Takahashi s.n. (paratype, KPM NC0010087), 15.ix.2003 H. Takahashi s.n. (holotype, KPM NC0011979; isotype, RET 383-1).
RET: JAPAN: OKINAWA-KEN—Ishigaki Isl., Ishigaki-shi, Banna-dake, 15.ix.2003 H. Takahashi s.n. (holotype, KPM NC0011979; isotype, RET 383-1).
The author gives the Japanese name for this species as "fuchidori-tamagotake."
—R. E. Tulloss
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