Appearance
The fruit bodies of ''Amanita onusta'' have caps that are initially broadly convex but flatten out as they mature, reaching diameters of 5 to 10 cm. The cap surface, grayish-white in color, is ornamented with conical or pyramidal raised warts, or flattened, symmetrically arranged gray to brownish gray, grayish brown or grayish-orange small scales that are densely arranged over the surface.The squamules are less crowded near the edge of the cap. The margin does not have striations, and is typically fringed with remnants of the veil. The gills on the underside of the cap are spaced closely together, and either free or narrowly attached to the stipe. They are white to cream color, and are interspersed with short lamellulae. The gills may look as if they are waterlogged.
The stipe is 5.5 to 12 cm long, 0.6 to 1.5 cm thick, and tapers slightly upwards. It is solid gray to brownish-gray near base, paler towards the top, and appears cottony or hairy. The bulb at the base of the stipe is roughly spindle- to turnip-shaped, and may root deeply into the soil, especially if the soil is loose.
The short-lived partial veil is white, and attached just below the top of the stipe. It is sticky and in maturity often clings to the upper part of the stipe, or may have some meagre remnants hanging from the cap margin. The universal veil remains are arranged in rows of warts and patches of gray to brownish-gray small scales over the upper portion of the bulb; below this, the color is a dirty white.
The flesh is firm and white. Fruit bodies can range in smell from mild to "slightly unpleasant". The odor has been described as resembling "chloride of lime", a smell similar to some bathroom disinfectants containing bleach.Viewed in deposit, such as with a spore print, the spores are white.
Viewed with a microscope, the spores are broadly ellipsoid to elongate, translucent, thin-walled, amyloid, and have dimensions of 8.3–11.6 by 4.9–6.6 μm. The basidia are 38–46 by 9–11 μm, club-shaped, mostly 4-spored but some are 2- or 3- spored, with clamps. The cheilocystidia are 23.3–31.5 by 11.6–15.7 μm, ellipsoid, club- to pear-shaped cells, partly in short rows. The cap cuticle is up to 168 μm thick, and consists of thin-walled interwoven hyphae that are 2–5.3 μm diameter, and gelatinized. Clamp connections are present in the hyphae of this species—these are short branches connecting one cell to the previous cell to allow passage of the products of nuclear division.
Naming
''Amanita onusta'' may be confused with ''A. cinereoconia'' because of the similar gray powdery veil remnants on the cap surface. ''A. cinereoconia'' is distinguished from ''A. onusta'' by the absence of clamps, its powdery-wooly to powdery-warty cap, as well as the absence of warts or scales at the base of the stipe. ''A. cinereoconia'' also smells distinctly of chloride of lime. Another similar species is ''A. costaricensis'', found only in Costa Rica. ''A. atkinsoniana'', another North American species, has shorter warts that are spaced further apart than those of ''A. onusta'', and the warts on the basal bulb are arranged in parallel rows.Distribution
''Amanita onusta'' grows solitary or scattered on the ground in mixed oak, hickory and chestnut forests from southern New England to Texas.Habitat
The species has a preference for sandy or loose soils. Its range extends north to Nova Scotia, Canada, and south to Mexico.References:
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