BRIEF DESCRIPTION: The cap is 24 - 102 mm wide, hemispheric at first becoming broadly convex to plano-convex, occasionally slightly depressed in center; white, pallid grayish-brown or grayish buff over disk in age, surface dull and tacky at first and becoming shiny; pileipellis peeling; context white, one specimen slightly browning where damaged, larva tunnels not discolored, 3 - 10 mm thick at center; margin nonstriate, incurved at first, then decurved, appendiculate; universal veil dense, finely pulverulent-flocculose, sometimes largely disappearing in age, especially over disk, white or at times grayish or brownish over disk where it infrequently comprises irregular, floccose warts sometimes darkening on tips.

The gills are narrowly adnate to adnate, sometimes with a decurrent line, close, whitish, becoming grayish-cream on drying, with white, floccose remnants of partial veil on edges, narrow, 4.5 - 11 mm broad, sometimes anastomosing; the short gills are truncate to rounded truncate to attenuate to attenuate in steps, plentiful, of diverse lengths, unevenly distributed.

The stipe is 25 - 142 × 5 - 20 mm, white, tapering upwards slightly with flaring apex, floccose especially in upper portion, material easily removed, with no bruising of flesh noted except in one specimen in which handling seemed to leave a faintly pinkish bruise; bulb subradicate or radicate, rarely narrowly oblong or subclavate, 22 - 72 × 8.5 - 27 mm, sometimes with brick red or rusty stains or spots, frequently flattened or doglegged; context white, occasionally graying in damaged areas, no discoloration in larvae tunnels or slightly brownish, easily breaking up into fibers, solid or with firmly stuffed central cylinder, up to 7 mm wide; partial veil fibrous-floccose and rapidly evanescent; universal veil absent from bulb and stipe base or difficult to distinguish.

The odor is indistinct or faintly of a tidal pool, rarely, faintly of disinfectant or cleansing powder, not unpleasant.

The spores measure (7.2-) 9.8 - 14.0 (-20.3) x (3.9-) 4.6 - 6.0 (-9.8) µm and are ellipsoid to elongate to cylindric (rarely bacilliform) and amyloid.  Clamps are absent from the bases of basidia.

In the field, A. longipes differs from A. chlorinosma (Peck in Austin) Lloyd macroscopically by its smaller habit, greater degree of radicating in the frequently curved or doglegged stipe, and the absence of the odor of decaying protein.  The densely floccose A. longipes appears to be much more common than A. chlorinosma in the sandy oak-pine woods of Long Island and the New Jersey Pine Barrens.  Very small, deeply radicating specimens of A. longipes might be confused with A. onusta (Howe) Sacc. in the field.  However, the volval material of A. longipes is always much paler than that of A. onusta and usually much more floccose.

This species is predominantly associated with oak and pine, but sometimes occurs in forests that also include beech, hickory, or birch.  The range of A. longipes extends from Long Island, New York to Alabama and Mississippi.

Elongate bulbs, narrow spores, and fruiting bodies deeply inserted in the soil are often associated with "leaky" ecosystems (Tulloss 2005).

Bas based his stirps Longipes on A. longipes. This stirps also includes A. amanitoides (Beeli) Bas of central Africa. -- R. E. Tulloss