Yellow-veiled Amanita

Amanita augusta is the yellow-veiled amanita of western North America, a handsome, medium to large species whose dark brown to olive-brown cap is set off by bright golden-yellow flecks of universal veil. Yellow reappears on the ring margin and in belts around the swollen stem base, making the colour scheme diagnostic once seen.

For most of the twentieth century western collections of this fungus were filed under the European name Amanita franchetii. Modern work separated them, and the western taxon was described as Amanita augusta, so older Pacific coast literature and photographs labelled A. franchetii generally refer to this species.

It belongs to the group of amanitas with amyloid spores and a bulbous, non-sac-forming base, sharing that architecture with Amanita rubescens and Amanita excelsa. Within western forests it is one of the more frequently encountered brown-capped amanitas of the rainy season.

Cap

5-14 cm across, convex then broadly flat, coloured dark brown, olive-brown, or yellow-brown, usually darkest at the centre and paler towards the margin. The surface bears numerous soft, floccose warts that are a striking golden or chrome yellow when fresh, fading to buff with age or rain. The margin is smooth to only faintly lined.

Gills

Free or very narrowly attached, crowded, white to cream, occasionally with a faint yellow tint on the edges. Short gills are numerous and truncate.

Stipe

7-15 cm long, whitish to pale yellow, often finely fibrillose and dusted yellow below the ring. The ring is membranous and skirt-like, characteristically yellow along its edge or on its underside. The base swells into an oval to club-shaped bulb encircled by belts and flecks of yellow veil material, without a sharp rim and without a free sac.

Flesh and spore print

Flesh white, sometimes tinted yellow just beneath the cap skin, essentially unchanging or only slowly and faintly discolouring where cut. Odour mild. Spore print white; spores ellipsoid and amyloid.

Amanita augusta occurs along the Pacific coast and interior west, from British Columbia through Washington and Oregon into California, with records extending into the Rocky Mountain states. It is mycorrhizal with conifers such as Douglas-fir, pine, and spruce, and also with oaks and other broadleaf trees in mixed woodland.

Fruiting follows the rains, chiefly from autumn into winter in the lowlands, and in spring at higher elevations after snowmelt. Fruit bodies appear singly or in scattered groups in needle duff, mossy litter, and along woodland trails.

This species is an ectomycorrhizal symbiont, forming a fungal mantle and Hartig net on the fine roots of conifers and oaks. That partnership supplies host trees with water and mineral nutrients drawn from a large soil volume in exchange for photosynthetic sugars, and it lets the fungus thrive in the acidic, needle-rich soils of western forests.

Its yellow pigment is deposited in the universal veil during the button stage, so the golden warts are present from the moment the cap breaks through and gradually wash pale over the life of the fruit body. Because both the cap warts and the basal belts derive from the same veil, a rain-stripped cap can still be identified by digging out the yellow-flecked bulb.

Amanita franchetii is the European counterpart and is functionally identical in structure but has a duller, more greyish-brown cap with paler mustard veil, and is not part of the western North American flora. Amanita gemmata reverses the colour pattern, with a pale yellow to buff cap carrying whitish warts, a grooved margin, and a bulb finished with a collar-like rim.

Amanita pantherina has a darker brown cap with pure white warts, a strongly grooved margin, and a sharply collared bulb. Amanita muscaria has a red to orange cap with white to cream warts and concentric rings of veil at the top of the bulb. The pairing of a brown cap with genuinely golden-yellow warts and a yellow-edged ring is what identifies Amanita augusta.