Felt-ringed Agaricus Identification Guide

The setting and the first impression

Agaricus hondensis is a fungus of coastal and near-coastal woodland in western North America, and the classic encounter is in deep duff under coast live oak, Monterey pine or Monterey cypress during the autumn and winter rains. It also appears in shaded landscaped ground, under planted conifers in parks, and along the mulched edges of paths. Fruit bodies come up singly, in scattered troops or in loose arcs, often half buried so that only a domed pale cap breaks the litter.

The first impression is of a solid, clean-looking white mushroom that turns out on closer inspection to be finely dressed in dull pinkish-brown fibres. It is a heavy fungus for its size, with a thick stipe, an obviously swollen base and a ring so substantial that it is visible from several paces. That ring is the reason for the English name and it is where the identification really starts.

Reading the cap

The cap is 5 to 15 cm across, occasionally larger, convex at first with the margin curved in, then broadly convex and finally almost flat with a low central flattening. The ground colour is white to dingy cream, and over it lies a coat of appressed fibrils and small flattened scales in vinaceous-brown, drab pinkish-brown or greyish-brown. These fibrils are densest at the centre, where they may form an almost solid disc, and thin out towards the margin so that the edge stays whitish.

Feel the surface. It is dry, silky, and never viscid. The margin usually carries hanging remnants of the partial veil in young specimens. Rub the cap firmly with a thumb and wait a few minutes: a slow, dull yellowish flush may appear, but it is far less dramatic than on some relatives, and it fades to brownish.

Gills, veil and the felted ring

The gills are free from the stipe, narrow, very crowded, and rounded at both ends. Colour is the standard Agaricus sequence but with a distinctive slow start: whitish to pale greyish-pink in the button, then a clean pink, then chocolate brown and finally dark brown-black as the spores mature. The pale grey-pink stage lasts noticeably longer here than in the pink-gilled field species, so a young specimen can look almost white-gilled.

The ring is the diagnostic structure. It is superior, sitting in the upper third of the stipe, thick, membranous and pendant like a skirt. Turn it over with a fingertip and examine the underside with a lens: it is felted and carries irregular cottony patches or a ragged wheel of flocci. This double-layered, patchy, felty ring separates the species instantly from the thin, smooth, single rings of many other white Agaricus.

Stipe, base and colour change

The stipe is 5 to 12 cm long and 1 to 2.5 cm thick, white, smooth and often shining above the ring and slightly fibrillose below. It is stuffed then hollow, and it ends in an abrupt, marginate bulb which is usually wider than the stipe is thick and may be flattened underneath. White mycelial cords bind the bulb into the duff, so lever it out whole rather than snapping the stipe.

Now cut the fruit body vertically. The flesh is white and thick in the cap. Watch the base of the stipe: within seconds to a minute the tissue inside the bulb flushes bright chrome yellow, sometimes intensely, before fading over half an hour to dull brownish or ochre. Rubbing rather than cutting produces the same yellow. The flesh higher in the stipe and in the cap changes very little.

Odour is a genuine field character here. Crush a fragment of the bulb between finger and thumb and smell it immediately: the scent is sharp, chemical, ink-like or phenolic rather than sweet and aromatic. Warming a small piece in a closed palm for a minute makes it much easier to detect.

Taking a spore print

Pick a cap in which the gills have gone chocolate brown but have not yet started to collapse. Cut the stipe off flush, lay the cap gills down on white paper, cover it with a bowl and leave it two to four hours. Because the deposit is very dark, white paper reads best, and there is no need for black card.

The print is a rich dark chocolate brown, occasionally with a purplish cast. That dark print, combined with free gills and a ring, places the fungus in Agaricus and its immediate allies and rules out white-spored, pink-spored and rusty-spored groups. Under a microscope the spores are small, smooth, thick-walled and ellipsoid, roughly 5 to 6.5 by 3.5 to 4.5 microns, without an obvious germ pore.

Substrate and season

The species is saprotrophic, living on woodland litter and buried plant debris rather than partnering a tree, but it is strongly associated with oak, pine and cypress duff along the Pacific coast. It favours deep, undisturbed litter in shade, and it responds to sustained rain rather than a single shower. Fruiting is essentially an autumn to midwinter event in its core range, running from the first serious rains until frost.

Separating it from look-alikes

Agaricus xanthodermus has a whiter cap that is smooth or only faintly fibrillose and often appears squared off or flat topped when young. Its yellow reaction is instant and brilliant, appearing on the cap margin as well as the bulb, and its ring is thinner and smoother beneath. The cap fibrils of Agaricus hondensis and the thick patchy ring are the separators.

Agaricus moelleri carries a much darker, denser mat of grey to blackish fibrillose scales, giving an overall grey cap rather than a pinkish-brown one, and its bulb yellows just as sharply.

Agaricus californicus is close and shares the habitat. It is usually smaller, its cap fibrils are greyer and sparser, and its ring is thinner with fewer cottony patches on the underside.

Agaricus augustus is much larger, with distinct tawny-brown scales on a ground that yellows readily, a shaggy stipe below the ring and a sweet aromatic rather than chemical odour.

Agaricus campestris has no bulb, a thin evanescent ring, bright pink young gills and no yellow reaction at all.

Finally, always confirm the print. Any white-spored fungus with free gills, a ring and a swollen base belongs to a completely different group, and the dark chocolate deposit settles the question in a few hours.