Amanita bisporigera - Amanitaceae.org - Taxonomy and Morphology of Amanita and Limacella
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name Amanita bisporigera
name status nomen acceptum
author G. F. Atk.
english name "North American Two-spored Destroying Angel"
images

  • 1. Amanita bisporigera, Vermont, U.S.A.


  • 2. The bright yellow response to 5% (or more concentrated) KOH (potassium hydroxide), Monmouth Co., New Jersey, U.S.A.



  • 3. Amanita bisporigera, New Jersey, U.S.A.



  • 4. Positive reaction to the Wieland Test indicating the probable presence of amatoxin in a specimen attributed to A. bisporigera, South Carolina, U.S.A.

    • intro Amanita bisporigera is a mushroom that often contains enough amatoxins to kill an adult human.  It extremely important that this species and its look alikes become familiar to anyone planning to collect mushrooms for the table in eastern North America.  This is one of the species that will often turn bright yellow in response to a drop of a strong base (like 5-10%KOH) on the cap.

    Advisory: This page contains a mixture of species that are presently being separated by genetic studies. Of the apparently distinct taxa that have been treated as A. bisporigera, all with the exception of the true A. bisporigera have 4-spored basidia.
    cap The cap of Amanita bisporigera is 25 - 100 mm wide, white, occasionally slightly straw yellow to pale tannish to pale pink to rose pink over the center especially in age or when sunburned or in hot and dry weather, sometimes slightly rusty in old wounds, convex to plano-convex, at times with a low broad umbo, slightly viscid when moist, with a nonappendiculate and nonstriate margin, decurved at first.  The volva is absent or present as a slight white flocculence on the margin in young fruiting bodies.  The flesh is white, unchanging, 5.5 - 6+ mm thick above the stem, thinning evenly for about one-third of the radius (until about 1 mm thick) then thinning more slowly towards the margin.
    gills The gills are free to barely adnate, crowded, white to off-white in mass, white to barely off-white in side view, unchanging when cut or bruised, 6 - 7.5± mm broad, pointed at both ends to subelliptical, with more tapering toward the stem, with minutely fimbriate (10x lens) white edge, with a sometimes slightly "wavy" edge, and with a decurrent tooth on the top of the stem.  The short gills are attenuate to subattenuate to truncate, and numerous.
    stem The stem is 55 - 140 × 5 - 20 mm, white, narrowing upward, expanded at the top, frequently floccose-fibrillose-squamose, may become smoother with age, and finely longitudinally striate.  The bulb is globose to subglobose to irregularly ellipsoid, sometimes subradicating, and 15 - 23 × 13 - 30 mm.  The ring is white, superior to subapical, membranous, thin, delicate, skirt-like, very faintly striate above (10x lens), persistent, may become shredded or slip down the stem.  The volva is limbate, with 2 or 3 lobes, reaching up to 38 mm from the base of the bulb, about 2 mm thick at the point half way between the attachment to the bulb and the uppermost point of the limb, membranous, white, unstained, becoming appressed to the stem, with no evident internal limb.  The flesh is white, unchanging when cut or bruised, solid to firmly stuffed and has whitish or slightly yellowing pith.
    odor/taste The odor is faintly pleasant at first, but becoming sickeningly sweet in age as in Amanita phalloides (Fr. : Fr.) Link.  This species is deadly POISONOUS.
    spores The spores measure (4.9-) 7.2 - 9.9 (-11.2) × (4.2-) 6.4 - 8.8 (-10.0) µm and are globose to subglobose to broadly ellipsoid, occasionally ellipsoid, very rarely elongate and are amyloid to strongly amyloid.  Clamps are absent at bases of basidia.
    discussion The species was originally described from western New York State (U.S.A.) and appears to have an extensive range from boreal forests on the island of Newfoundland to pine-oak (Pinus-Quercus) forests in Texas.  There is a very similar taxon that responds weakly or negatively to KOH solution in southeastern Arizona and central Mexico.  Amanita bisporigera has possibly been exported to pine plantations as far south as Colombia.  It is known from the Americas only.

    Note the yellow reaction to 10% KOH solution on the cap in the background photograph.

    Amanita bisporigera is deadly POISONOUS. The reader may wish to compare this species with an east Asian 2-spored "Destroying Angel"—A. exitialis Zhu L. Yang & T. H. Li—and the 4-spored east Asian taxa A. subjunquillea var. alba Zhu L. Yang and the European A. virosa (Fr.) Bertillon in DeChambre.  We also refer to the recently revised key to the taxa of sect. Phalloideae in North America.—R. E. Tulloss
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