Milky Mushroom Identification Guide

The Setting and the First Impression

Calocybe indica is a fungus of warm, humid, lowland tropics, described from India and best known across South Asia. The setting is a monsoon one: humus-rich soil in gardens and plantations, roadside banks, grassy ground with plenty of incorporated plant debris, decaying straw and leaf accumulations, appearing during and just after the rains when the ground is saturated and daytime temperatures stay high.

The first impression is of an unusually clean, solid, entirely white mushroom. It stands well clear of the ground on a thick stem, the cap is fleshy and smooth, and the whole fruit body has a firmness that distinguishes it immediately from the soft, fast-collapsing agarics that dominate tropical grassland after rain. Fruit bodies occur singly, scattered, or in small groups, and they persist for days rather than hours.

An all-white, heavy-bodied agaric on soil is exactly the shape that demands the most careful routine, because several very different genera converge on it. The discipline that matters here is not the cap but the base and the spore print, so plan to excavate every specimen fully and to print at least one.

Reading the Cap

Caps are large, typically 5 to 14 cm across and occasionally more on well-fed specimens. Young caps are hemispherical to convex with a strongly inrolled margin, then broadly convex, and finally flattened or very shallowly depressed with a wavy, uplifted margin in age.

The surface is dry, smooth to very finely silky, and matt rather than shiny. It is not viscid, not scaly, and not fibrillose in any obvious way, though the disc can become minutely cracked or areolate in specimens exposed to hot sun after rain, and the margin sometimes splits.

Colour is white to milky white throughout, sometimes ageing to ivory or the faintest cream at the centre. There are no scales, no patches of adhering veil tissue, no warts and no coloured zoning. Absence of veil patches is itself worth recording, because a scatter of removable white flakes on a white cap points elsewhere.

The flesh beneath the cap surface is thick, especially over the disc, and this thickness is part of the species' character: the cap does not feel papery or thin at any stage.

Reading the Gills

Turn the cap and inspect the attachment carefully with a knife-cut through the stipe apex if needed. Gills are sinuate to adnexed, notched where they meet the stipe, and in some specimens they appear almost free. They are crowded, narrow to moderately broad, thin, with several tiers of shorter intermediate gills and occasional forking near the margin.

Colour is white and, importantly, it stays white. Even in fully mature specimens with a well-developed cap the gills remain white to the palest cream, never going pink, never going grey, never going brown or chocolate. Watching a mature specimen and confirming that the gills have not darkened is a decisive step, because the pink-gilled and brown-gilled white agarics are the commonest confusions.

Gill edges are even and concolorous. Damaged gills do not stain or discolour appreciably.

Stipe, Base and Flesh

The stipe is stout, central, and solid, usually 4 to 9 cm tall and 1 to 3 cm thick, cylindrical or tapering slightly upward, sometimes swollen toward the base. It is white, dry, smooth or finely fibrillose-striate lengthwise, and firm enough to resist bending.

Now the most important step in the whole routine: excavate the base completely. Use a knife or trowel and lift the fruit body with the soil around it intact, then wash or brush the base clean.

What you should find is a simple, tapering or slightly bulbous base with white mycelial threads binding soil and plant debris, and nothing else. Specifically confirm all of the following absences.

No volva. There must be no membranous sac, cup, collar, or free rim of tissue around the base, and no soft bag left in the ground when the fruit body is lifted.

No ring. There must be no membranous skirt, no collapsed collar, and no fibrous ring zone anywhere on the stipe.

No pseudorhiza. There must be no long, tapering, root-like extension diving deep into the ground.

Flesh is white, thick, firm and compact throughout cap and stipe, and it tears fibrously rather than snapping like chalk. Cut a fruit body in half lengthwise and leave the surfaces exposed for ten minutes: there should be no colour change at all, no yellowing, no reddening, no browning and no blueing.

Taking and Reading the Spore Print

The print is what closes the identification, and on an all-white mushroom it must be read carefully rather than glanced at.

Cut the stipe flush with the gills, set the cap gills-down on white paper with a slip of glass, foil or dark card under one half, cover it with a bowl to keep the humidity up in the warm air, and leave it for six to twelve hours. In hot conditions keep the covered cap somewhere cool so it does not dry before depositing.

The print is white. Judge it against both backgrounds and scrape the deposit into a small heap with a blade before deciding, because a thin white scatter on white paper can be almost invisible while a heaped deposit is obvious. Under the microscope the spores are small, smooth, hyaline, thin-walled and ellipsoid to broadly ellipsoid, roughly 5 to 7 by 3 to 4.5 micrometres, with no reaction in iodine-based mountants. The basidia carry siderophilous granules, a technical genus-level character.

Substrate, Season and Ecology

This is a saprotroph of rich soil. It fruits from humus, decaying plant litter, incorporated straw and organic debris rather than from living roots or standing deadwood, so it turns up in gardens, plantation floors, banks, waste ground and grassy areas where organic matter has accumulated and been worked into the soil.

Its requirements are strongly thermophilic. Fruiting depends on sustained warmth combined with high humidity, which in South Asia means the monsoon and the weeks that follow it. In seasonally dry climates the mycelium persists in the soil through the dry period and fruits again when rain returns.

Because the fruit bodies are firm and thick-fleshed, they last several days in the field, and mature specimens frequently become insect-tunnelled through the stipe before they decay.

Separating It from the Look-alikes

White Amanita species are the most important morphological confusion anywhere in the tropics, and they share the white cap, white gills and white spore print. The separation is at the base and the stipe: Amanita fruit bodies emerge from a universal veil and therefore show a volva as a sac, rim, collar or ring of loose tissue at the base, and most also carry a membranous ring on the stipe. Their gills are truly free, not sinuate. Never identify a large white agaric without lifting the base intact.

Volvariella volvacea and its relatives also have a conspicuous sac-like volva, but they additionally give a pink to salmon spore print and their mature gills turn pink. Both characters exclude the Milky Mushroom outright.

Agaricus species have a membranous ring, free gills that darken through pink to chocolate brown, and a dark brown spore print.

Leucoagaricus and Chlorophyllum species have free gills, a ring on the stipe, and frequently a scaly or fibrillose cap; some give a green print.

Termitomyces species share white gills and a pale print but grow from termite comb, and the base tapers into a long, tough, root-like pseudorhiza running deep into the ground toward the nest. Many also have a pointed apex on the cap.

Pleurotus species have decurrent gills, an eccentric or lateral stipe or none at all, and grow on wood, with a lilac-tinted print in some species.

White Clitocybe and Leucopaxillus species have decurrent gills and a funnel-shaped cap, and are thinner-fleshed.

Quick Field Checklist

• Large, entirely white, firm-fleshed agaric on humus-rich soil in warm humid conditions
• Dry, smooth, matt cap without scales or adhering veil patches
• Crowded sinuate to adnexed gills that stay white at every age
• Stout solid white stipe with no ring, no volva at the base, and no deep root-like extension
• White flesh with no colour change on cutting; white spore print with small smooth spores