Weeping milk cap

Appearance

The fruit body of "Lactifluus volemus" has a fleshy and firm cap with a velvety or smooth surface and a shape that changes with maturity: it starts off convex, with edges curved inwards, then later grows flat with a depression in the middle. With a typical diameter of 5 to 11 cm, its colour ranges from apricot to tawny.

The cap colouration, however, is somewhat variable, as has been noted in Asian, European, and North American specimens. The stem, whose height varies between 4 and 12 cm, and which is typically between 1 and 1.5 cm thick, has a slightly lighter colouration than the cap.

It is firm, with a velvety or smooth surface that sometimes has depressions running longitudinally up and down its length. The gills are adnate to slightly decurrent, brittle, narrow, quite closely spaced and sometimes forked. Normally a pale golden yellow colour, the gills turn brown when bruised. Interspersed between the gills are lamellulae, short gills that do not extend to the stem. The flesh is whitish and firm. The mushroom smells somewhat fishy; one source suggests the odour is "like a dead shad, which anglers will tell you is probably the most malodorous freshwater fish".

The odour is concentrated when the fruit bodies are dried. One of the mushroom's most distinctive features is the abundant latex, so plentiful that a small nick on the gills will cause it to "weep" the milky substance. The latex tends to impart brown stains on whatever it contacts.The spore print is whitish. The spores are roughly spherical, translucent, and typically measure 7.5–10.0 by 7.5–9.0 µm. The spore surface is reticulate—covered with ridges that form a complete network. The ridges are up to 0.8 µm high and have conspicuous projections up to 1.2 µm high. The spore-bearing cells of the hymenium, the basidia, are club-shaped, hyaline, four-spored, and have dimensions of 40–62 by 7.2–10.4 µm. Interspersed among the basidia are sterile cells called cystidia. The pleurocystidia are roughly spindle- to club-shaped, and measure 48–145 by 5–13 µm. The cheilocystidia may be spindle-, club-, or awl-shaped, or intermediate in between these forms, and measure 27–60 by 5–7 µm. Additionally, there are cystidia present on both the surface of the cap and the stem. If a drop of ferric sulphate is applied to the mushroom flesh, it will immediately stain dark bluish-green.

Distribution

"Lactifluus volemus" is found in warm temperate regions and as well as some subtropical and tropical regions of the Northern Hemisphere. The fungus is widely distributed throughout Europe, although it is in decline in some countries, and has become rare enough in the Netherlands to be considered locally extinct. In the Americas, the northern limit of its distribution reaches southern Canada east of the Great Plains, and the species extends south to the East Coast of the United States and Mexico, and beyond into Central America. It is also known from Asia, including China, Japan, India, Korea, Nepal, and Vietnam. Collections have also been made from the Middle East, including Iran and Turkey.

Habitat

Like all milk caps, "L. volemus" forms ectomycorrhizae, mutually beneficial symbiotic associations with various tree species. In this association, the fungal hyphae grow around the root of the plant and between its cortical cells, but do not actually penetrate them. The hyphae extend outward into the soil, increasing the surface area for absorption to help the plant absorb nutrients from the soil. It is found growing at the base of both coniferous and broad-leaved trees, although it is more common in deciduous woods. It may also sometimes be found in peat moss beds. The fruit bodies, which appear between summer and autumn, are common. They can be found growing solitarily or in groups, and are more abundant in weather that is warm and humid.

Fruit bodies can be inhabited by species of limoniid flies, such as "Discobola marginata" or "Limonia yakushimensis", as well as several species of fungi-dwelling mites. The flies are hosts for the mites in a symbiotic association known as "phoresis", whereby the mites are mechanically carried by its host. Mites are small and unable to migrate the relatively long distances between mushrooms without assistance; the insect hosts, in comparison, are large and can transfer the mites between their preferred feeding habitats.