Cleft-foot Amanita
Amanita brunnescens
Also called cleft-footed amanita, brown american star-footed amanita
An eastern North American amanita recognised by its dark brown, patch-flecked cap and by the abrupt basal bulb that splits into vertical clefts. Cut or bruised tissue slowly darkens to reddish brown.
Overview
Amanita brunnescens is among the most abundant amanitas of eastern North American woodlands, appearing in enormous numbers in warm, wet summers. Its Latin epithet refers to the browning reaction of its flesh, and its common name refers to the extraordinary stem base, which typically cracks into several vertical clefts as it expands, giving a split-hoof or star-footed appearance.
The species belongs to the section of Amanita containing firm-fleshed, amyloid-spored species with a bulbous rather than sac-like stem base, a group that also includes Amanita rubescens, Amanita citrina, and Amanita porphyria. Unlike the grisettes, it has a well-developed ring; unlike the death-cap group, it lacks a loose membranous volva.
A pale form, sometimes treated as var. pallida, has a whitish to very pale grey-brown cap but shares the cleft bulb and the browning flesh, so the base and the discolouration are far more reliable than colour alone.
How to identify it
Cap
5-12 cm across, convex becoming flat, sometimes with a broad low umbo. Colour ranges from dark chocolate or greyish brown at the centre to paler brown or almost whitish towards the margin, with an overall streaky, water-soaked appearance. A few thin, whitish to greyish membranous patches of universal veil usually sit on the disc but often wash away. The margin is smooth, not grooved.
Gills
Free, crowded, white to slightly cream, becoming spotted or edged with brown where handled or where insects have fed. Short gills with abruptly cut ends alternate with the full-length gills.
Stipe
6-14 cm long, white to pale brownish, smooth to slightly fibrillose, often with faint brown streaks. The ring is membranous, white, skirt-like and hangs freely; it can tear away in age. The base forms an abrupt, rounded to turnip-shaped bulb with a distinct rim, and this bulb characteristically splits into two or more vertical clefts, sometimes deep enough to look sliced.
Flesh and spore print
White, firm, slowly staining reddish brown to dull vinaceous brown where cut, bruised, or tunnelled by insect larvae; the discolouration is most obvious in the stem and bulb after twenty minutes or so. Odour faint, sometimes slightly of raw potato. Spore print white, spores globose and amyloid.
Where and when it grows
This species is mycorrhizal with hardwoods and conifers, above all with oaks, but also with beech, birch, hemlock, and pine. It grows singly, scattered, or in loose troops on soil and leaf litter in deciduous and mixed forest, and is equally at home in suburban oak plantings and in mature woodland.
Its range covers eastern North America from southeastern Canada to the Gulf Coast and west to the Great Plains, with similar-looking taxa reported from eastern Asia. Fruiting begins in early summer and continues into autumn, with the heaviest flushes in humid weather following prolonged rain.
Ecological role
Amanita brunnescens is an ectomycorrhizal symbiont. Its hyphae form a dense mantle around fine root tips and a network of hyphae between the root cortical cells, greatly extending the volume of soil a tree can draw water and nutrients from. In return the fungus receives photosynthetic sugars, which it uses to build the large fruit bodies seen above ground.
Because it partners with several common canopy trees and tolerates a range of soil conditions, it is an ecological generalist and often one of the first amanitas to appear in a season. The browning reaction seen in cut flesh comes from oxidation of pigment precursors on exposure to air, the same general process that darkens a cut apple, and is a useful field character rather than an ecological one.
Similar species
Amanita porphyria has a similar dark cap but with a distinct purplish-grey cast, a grey ring, and a rounded, sharply rimmed bulb that does not split into clefts; its flesh does not brown. Amanita citrina is paler lemon-yellow to whitish, has a rounded rimmed bulb, and likewise fails to develop the reddish-brown staining.
Amanita phalloides, the Death Cap, shares a smooth non-grooved cap but is usually greenish to olive with a metallic sheen and radiating dark fibrils, and crucially has a loose, membranous, sac-like volva enclosing the base instead of a cleft bulb. Amanita rubescens develops pink to wine-red rather than brown discolouration and has a grooved ring and a bulb without clefts.