Pelargonium Webcap Identification Guide

First Impression and Setting

This is a small, dark, unassuming mushroom that is easy to walk past and surprisingly easy to name once you know the routine. The setting is damp autumn woodland: birch on wet acid ground, mossy conifer edges, Sphagnum lawns and boggy hollows, often among Polytrichum or Sphagnum with the fruitbodies pushing up through the moss on long thin stems.

What catches the eye is contrast. The cap is dark date- or umber-brown when moist, and it is dusted or frosted with whitish veil fibrils and small scales, so it looks as if it has been lightly powdered with frost. The stem is slender, wavy and banded with white girdles on a brown ground. Small dark Cortinarius species are a notoriously hard group, but this one has a chemical shortcut, described below, that removes most of the doubt.

Reading the Cap

The cap is 1.5-4 cm across, conical to bell-shaped at first, expanding to convex with a sharp persistent umbo. The margin is often ragged with veil remnants and may be faintly translucent-striate when very wet.

The surface is dry and matt, dark umber, date brown or blackish brown when moist, and it is strongly hygrophanous: as it dries out the ground colour pales through mid-brown to ochre-tan, usually from the margin inwards, leaving the umbo darkest. Over this ground lie the white to silvery veil fibrils, sometimes flattened as radial silky streaks, sometimes raised as tiny woolly scales, and densest towards the margin. On old, weathered caps the white coating can wash off almost completely, which is why age and moisture state should be recorded when you collect.

The Odour Test

Crush a fragment of cap or stem flesh between finger and thumb and sniff immediately. Cortinarius flexipes carries a strong, sharply green, resinous scent exactly like the crushed leaves of a scented pelargonium, the plant most people call a geranium. It is one of the most reliable scents in the entire genus, and in a small dark webcap it is close to decisive.

The scent is strongest in fresh, moist material and in the stem base. If a candidate has no smell at all, or smells earthy or spermatic, work through the alternatives instead of forcing the name.

Gills, Cortina, Stem and Flesh

The gills are adnate to slightly notched, moderately distant, fairly broad, and pale greyish clay or beige with a faint violaceous tinge in the very youngest specimens. They darken steadily through cinnamon to deep rust-brown as the spores ripen, and the edge stays paler and slightly uneven.

Across the young gills runs the cortina, the cobwebby partial veil that names the genus, a sparse white web from cap margin to stem. It collapses onto the upper stem and, once spores begin to fall, marks it with a rust-coloured fibrillose zone.

The stem is 3-8 cm long but only 2-5 mm thick, cylindrical, often distinctly flexuous or curved, hollow when mature, and fragile. Its ground colour is pale brown to greyish, and over it the white universal veil is arranged in irregular transverse bands, girdles or a woolly sock, usually strongest below the ring zone and often reaching a small white-downy base. Those white bands on a slender wavy stem are a strong supporting character.

Slice it lengthwise. The flesh is thin, brown and watery in the cap, paler in the stem, with no marked colour change on exposure, no latex and no bruising reaction. What you get instead is a fresh release of the pelargonium scent.

Spore Print and Microscopy

Detach the cap, place it gill-side down on white paper, cover it and leave it three to six hours. Small hygrophanous caps dry out fast, so keep a damp scrap of tissue nearby. The print is rust-brown.

Microscopically the spores are ellipsoid to broadly almond-shaped, about 7-9.5 x 4.5-6 microns, and finely warted. Smooth spores or a print in any other colour take you out of Cortinarius entirely, most often into Inocybe or Galerina territory.

Substrate, Season and Ecology

Cortinarius flexipes is ectomycorrhizal, forming root sheaths with birch above all, and also with spruce and pine in mixed and boreal woodland. It favours damp, acid, mossy ground: bog margins, Sphagnum carpets, wet birch scrub, moss-carpeted conifer plantations and heathy woodland edges.

It fruits from late summer through autumn, often singly or in small scattered groups rather than dense troops, and often half-hidden with only the umbo showing above the moss. Because the fruitbodies are small and dark, the practical search technique is to look for the pale stems rather than the caps: the white banding stands out against green moss more than the umber cap does.

Separating the Look-Alikes on Morphology

Cortinarius paleaceus is the nearest relative and is treated by some authors as a variety of the same species. It carries the same pelargonium scent but has a shaggier, more coarsely scaly white veil covering on the cap and typically occurs with conifers and in Sphagnum. Separation rests on veil texture and habitat, and intermediate collections are common; recording the veil carefully is the best you can do in the field.

Cortinarius hemitrichus is the classic birch confusion. It is larger, with a more campanulate cap covered in white fibrils, but the odour is insignificant or faintly earthy rather than pelargonium-like, and the veil bands on the stem are usually less crisp.

Cortinarius bivelus and other telamonias are altogether stouter, with thicker stems and a clubbed base.

Inocybe species overlap in size, colour and damp mossy habitat, and this is the genus to rule out deliberately. Inocybe caps are radially fibrillose and frequently split at the margin, they lack a true cobwebby cortina and the white transverse veil bands, their prints are dull clay-brown rather than warm rust, and many have a distinctly spermatic odour.

Galerina species in Sphagnum are more ochre, translucent-striate, smooth-capped, and lack the white flocculose covering; their spores are ornamented differently and the caps are glossier when wet.

Field Checklist

Small dark umber hygrophanous cap with a pointed umbo and white frosting; slender flexuous stem with white transverse veil bands and a rusty cortina zone; gills clay then rust; strong crushed-geranium scent; rust-brown spore print; damp mossy birch or conifer ground in autumn.