Amanita arkansana

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by Michael Kuo

Amanita arkansana is a large member of the Amanita caesarea species complex, associated with oaks east of the Great Plains, generally south of a line between Kansas City and Washington DC (roughly Interstate 70). When young its cap is yelow-orange, but as the mushrooms mature the orange hues can diminish, resulting in yellow or even brownish caps, usually with a somewhat darker center. The cap regularly reaches 15 cm in width, and the stem is often 2 cm thick or more. Under the microscope, Amanita arkansana has spores that are mostly 8–10 µm in length.

Similar species include Amanita jacksonii, which is red when young, becoming reddish orange, and Amanita species 04, which is much smaller, lacks orange shades when young, has longer spores, and is distributed from Interstate 70 northward. There is overlap between Amanita arkansana and Amanita species 04 in physical features and in range, but typical specimens of each species are fairly easily separated.

Description:

Ecology: Mycorrhizal with oaks; summer; distributed east of the Great Plains from roughly I-70 southward. The illustrated and described collections are from Illinois and Indiana.

Cap: 8–16 cm across; oval at first, expanding to convex and, later, planoconvex; bald; sticky when fresh, but soon dry; when young yellowish orange with or without a yellow marginal area, becoming yellowish orange to yellow overall, with a brownish orange to brownish yellow center; without warts or patches; the margin grooved for several centimeters.

Gills: Free from the stem or slightly attached to it; whitish to pale yellow; close; not discoloring; short-gills present.

Stem: 10–20 cm long; 1–2.5 cm thick; tapering slightly to apex; base even, or with a slight bulb; dry; bald or finely silky; whitish to yellowish; with a white to pale yellow, skirtlike ring and a white, sacklike volva.

Flesh: White; not staining on exposure.

Odor: Not distinctive.

Spore Print: White.

Microscopic Features: Spores 8–10 x 5–7 µm; broadly ellipsoid to subamygdaliform; smooth; hyaline in KOH; inamyloid. Basidia 4-sterigmate. Hymenial cystidia not found. Subhymenium cellular. Pileipellis an ixocutis of elements 2–4 µm wide, hyaline to yellowish in KOH.

REFERENCES: Rosen, 1926. (Jenkins, 1986; Tulloss, continuously updated.) Herb. Kuo 07080707, 06220803, 06271001, 07181615.

This site contains no information about the edibility or toxicity of mushrooms.

Spores

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Kuo, M. (2020, February). Amanita arkansana. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/amanita_arkansana.html