Lactarius argillaceifolius

Appearance

The cap is 4–18 cm wide, and initially convex to broadly convex before flattening out with a depressed center. The cap margin is curved inward, and often remains that way into maturity. The cap surface is covered with fine soft hairs when young, but later becomes smooth; it is slimy and sticky when wet. The color of the cap ranges from lilac-brown when young, fading to lilac-tan or pale lilac-gray and eventually to pale tan or pinkish-buff at the center. The gills are attached to slightly decurrent , broad, and packed together closely. They are cream-colored when young, and later develop pinkish tones near the margin. In maturity, they become flushed with brownish-orange. The color stains buff to olive-brown to dark brown when bruised.

The stem is 6–9 cm long by 1.5–3.5 cm thick, and nearly equal in width throughout or tapering downward. Its surface may be slimy or dry, depending on the moisture in the environment. It is whitish, but in age becomes spotted with brownish stains. The flesh is firm, and white to buff. Its odor is not distinctive, while its taste is mild or slowly becomes slightly acrid. The latex is creamy-white on initial exposure, and stains the gills grayish-brown to dark brown or olive-brown; its taste is mild or slowly becomes slightly acrid. Older fruit bodies tend to have less abundant and weaker-tasting latex. The spore print is pinkish-buff. The edibility of ''L. argillaceifolius'' is unknown. The cap surface will turn yellow to orange when a drop of dilute potassium hydroxide is applied.The spores are roughly spherical to broadly elliptical, and measure 7–11 by 7–8 µm. They are ornamented with warts and ridges that sometimes form a partial reticulum , with prominences up to 1 µm high. The spore are hyaline and amyloid, meaning that they will absorb iodine when stained with Melzer's reagent. The cap cuticle of young specimens is made of a tissue type known an ixotrichoderm, which contains gelatinized hyphae of different lengths arranged in roughly parallel fashion. As the mushroom matures, the cap cuticle gradually becomes an ixolattice—characterized by branching, entangled, gelatinous hyphae. The basidia are four-spored, and measure 45–52 by 9–10.5 µm. The pleurocystidia are abundant, and relatively long—between 60–140 µm long by 6–14 µm thick. The cheilocystidia measure 32–67 by 6–9 µm.

Naming

''Lactarius trivialis'' is a European species that is similar in appearance to ''L. argillaceifolius'', and they are often confused for each other. ''L. trivialis'' can be distinguished by gills that stain brown when exposed to the latex, and a preference for growing in conifer- and birch-rich boreal and subalpine forests. Variety ''megacarpus'' may be confused with ''L. pallescens'', a smaller paler-colored species with latex that stains gills lilac rather than brown.

Distribution

Like all ''Lactarius'' species, ''L. argillaceifolius'' is mycorrhizal. The fruit bodies of ''Lactarius argillaceifolius'' grow scattered or in groups on the ground under hardwoods, especially oak, from July to October. It is often one of the first mycorrhizal mushrooms to fruit in forests dominated by oak and hickory. The fruit bodies are slow to develop and are long-lasting. The species is found from eastern Canada south to Florida, and west to Minnesota and Texas. It is common in northeast Mexico. The mushroom has also been reported from southern Brazil growing in association with pine plantations, where it has probably been introduced with pine seedlings brought by settlers. ''L. argillaceifolius'' var. ''megacarpus'' has been collected from Baja California, California, Oregon, and Washington, where it grows in association with coast live oak and tanoak.

Habitat

Like all ''Lactarius'' species, ''L. argillaceifolius'' is mycorrhizal. The fruit bodies of ''Lactarius argillaceifolius'' grow scattered or in groups on the ground under hardwoods, especially oak, from July to October. It is often one of the first mycorrhizal mushrooms to fruit in forests dominated by oak and hickory. The fruit bodies are slow to develop and are long-lasting. The species is found from eastern Canada south to Florida, and west to Minnesota and Texas. It is common in northeast Mexico. The mushroom has also been reported from southern Brazil growing in association with pine plantations, where it has probably been introduced with pine seedlings brought by settlers. ''L. argillaceifolius'' var. ''megacarpus'' has been collected from Baja California, California, Oregon, and Washington, where it grows in association with coast live oak and tanoak.