Yellow Patches Identification Guide

The first impression

You are in eastern North American woodland in high summer or early autumn, somewhere with hemlock, oak, beech or birch overhead and a deep, damp litter layer underfoot. A patch of bright orange-yellow catches your eye at ground level, and as you crouch, the colour resolves into a small to medium Amanita with a scattering of vivid yellow crumbs on the cap, white free gills, and a slender white stem rising from a rounded bulb. Amanita flavoconia is one of the more visually distinctive small Amanitas of the region, and once you have learned its colour combination, orange cap plus chrome-yellow powdery warts plus yellow crumbs at the base, most finds are named in seconds. The care goes into ruling out the several other yellow-warted Amanitas that overlap with it.

Working the cap

Size and shape. Three to eight, occasionally ten centimetres across. Egg-shaped to bluntly conical when young, expanding through convex to broadly convex and finally almost flat, often with a low central hump.

Colour. Bright orange-yellow to yellow-orange, usually strongest at the centre and fading outward toward a paler yellow rim. The pigment sits in the cuticle, not in a separate layer, so it does not wash away.

Surface and veil remnants. This is the diagnostic feature. Scattered across the cap are bright chrome-yellow to golden warts, remnants of the universal veil, which are powdery, floccose and extremely friable. Rub one with a fingertip and it crumbles to dust rather than peeling off as a leathery patch. A single heavy rainstorm will strip most of them, so a bare cap does not rule the species out, but a fresh specimen nearby will usually still be decorated. The cap surface is slightly tacky in wet weather and dry and slightly shining when dry.

Margin. Even and not, or only faintly, striate. A strongly grooved, tyre-tread margin should make you look harder at the alternatives.

Gills, stem and base

Gills. Free from the stem, or barely reaching it, crowded, moderately broad, white to pale cream, sometimes with a faint yellow tint along the edge. Short gills are truncate. The gill edges are minutely fringed when viewed with a lens.

Stem. Five to twelve centimetres tall and slender, white to pale yellow, often finely floccose or dusted with yellowish flecks, hollow or loosely stuffed in age, tapering slightly upward.

Ring. A skirt-like membranous ring hangs from the upper stem, usually pale yellow at least on its underside or margin, sometimes yellow throughout. It is thin and often collapses against the stem or tears away entirely in older or weather-battered material.

Base. Dig, do not pull. The full base is essential and easily left in the ground. Amanita flavoconia has an oval to rounded basal bulb that is not sheathed in a membranous sac and not sharply rimmed. Instead, the universal veil persists as bright yellow powdery patches, flecks and crumbs adhering to the bulb and to the soil immediately around it. Those yellow crumbs in the excavated hole are as diagnostic as anything on the cap.

Flesh. White throughout, sometimes yellowish immediately under the cap cuticle. Crucially, the flesh does not change colour on cutting or bruising. No reddening, no blueing, no slow browning beyond the ordinary drying discolouration.

Spore print and micro characters

Set a mature cap gills-down on split black and white card under a cup for two to four hours. The print is white. That, plus free gills and a universal veil, places the fungus in Amanita and eliminates a great many brown-, pink- or rust-spored genera at a stroke.

Under the microscope the spores are ellipsoid and smooth, roughly 7 to 9 by 5 to 6 micrometres, and importantly they are amyloid, turning blue-grey to blackish in Melzer's iodine. That amyloid reaction places the species in section Validae rather than in the inamyloid-spored groups, and it is the cleanest way to separate it from several superficially similar orange Amanitas. Clamp connections are present at the bases of the basidia.

Habitat, partners and season

Amanita flavoconia is ectomycorrhizal, forming root partnerships with both conifers and hardwoods. Eastern hemlock is a strongly associated partner, but oak, beech, birch and pine all support it. It fruits from early summer through to mid autumn, singly or scattered rather than in tight clusters, on soil and in litter in mixed and coniferous forest across eastern North America. Its abundance in a given season tracks summer rainfall closely, and it is one of the more frequently encountered small Amanitas in that range.

Separating the look-alikes on structure alone

• Amanita muscaria var. guessowii shares a yellow to orange cap but is far larger and stouter, its warts are whitish to cream rather than chrome yellow, and its bulb carries several concentric rings or bands of veil tissue like shoulders rather than loose yellow crumbs.
• Amanita frostii is smaller, with a distinctly striate cap margin, a bulb topped by a narrow collar or rim, and, under the microscope, globose to subglobose spores rather than ellipsoid ones.
• Amanita flavorubens (flavorubescens) also has yellow warts on a yellowish cap, but its flesh and stem stain reddish where cut, handled or insect-damaged. Cut one lengthwise and wait: reddening rules out flavoconia.
• Amanita gemmata is pale straw to pale yellow rather than orange, its warts are whitish and often larger and flatter, the ring is flimsy, the cap margin is distinctly striate, and the bulb has a small collared rim.
• Amanita banningiana is a clearer, purer yellow with a strongly striate margin and a very different veil expression.
• Cystoderma and Pholiota species may look granular and yellowish from a distance but have attached gills, no free-gill construction and no true bulb with universal veil remnants.

Recording a find well

Photograph the cap from above to show warts, the underside to show free gills and ring, and the excavated base against a dark background so the yellow flecks read clearly. Note the trees within ten metres, whether the margin was striate, and above all whether any cut surface changed colour. Those four notes will resolve nearly every Amanita flavoconia record without recourse to a microscope.