Amanita hyperborea - Amanitaceae.org - Taxonomy and Morphology of Amanita and Limacella
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name Amanita hyperborea
name status nomen acceptum
author (Karst.) Fayod
english name "White Flour Amanita"
intro The description that follows is based upon the treatment of this species by Bas (1982).
cap The cap of A. hyperborea is up to 60 mm wide, convex to plano-convex, probably originally umbonate, dull to somewhat shiny, thin-fleshed, with a rather strong and dense sulcate margin (20 - 50% of the radius).  The cap is white in the center.  The volva is present as small, subconical white warts or felted patches in the center of the cap.
gills The gills are free, crowded, probably rather narrow, probably with a minutely flocculose edge, and white.  Short gills are present.
stem The stem is relatively short, up to 40 mm long, moderately thick, white, without a ring, slightly fibrillose, with a narrowly clavate to subbulbous base.  When dried, the base is 75% wider than the stem.  Volval warts or patches are small, vague, white, felted subflocculose, and present on the lower quarter of the stem.  In Bas' drawing, he shows the volva rather low on the stem.
spores The spores measure 11.2 - 13.3 (-13.8) × 9.4 - 10.8 (-11.3) µm and are inamyloid and subglobose to broadly ellipsoid, rarely ellipsoid, sometimes broadened subapically so that they appear egg-shaped.  Clamps are absent at bases of basidia.
discussion It was originally described by Karsten in Russian Lapland.  Earlier Karsten had found what he believed was the same species in the bank of the river Tuloma in Russian Lapland among grasses in the sandy bank of the Tuloma River.

In 1982, Bas stated that this species was known only from the type.  Bas points out that this species has often been mistakenly placed in section Vaginatae however it appears to be more closely related to A. friabilis (Karst.) Bas and A. farinosa Schwein.—R. E. Tulloss and L. Possiel
brief editors RET

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