Lactifluus volemus, formerly known as Lactarius volemus, and commonly known as the weeping milk cap or bradley, is a species of fungus in the family Russulaceae. Phylogenetic analysis suggests that L. volemus represents several species or subspecies, rather than a single taxon. The colour of the mushroom varies from apricot to tawny, and the cap may be up to 11 cm (4+1⁄2 in) wide. The pale golden yellow gills on the underside of the cap are closely spaced and sometimes forked. One of the mushroom's most distinctive features is the large amount of latex it exudes when the gills are damaged, leading to some of its common names, e.g. voluminous-latex milky. It also has a distinctive fishy smell, which does not affect the taste. The fruit bodies have been chemically analysed and found to contain several sterols related to ergosterol, some of which are unique to this species. The mushroom also contains a natural rubber that has been chemically characterized. L. volemus produces a white spore print and has roughly spherical spores about 7–8 μm in diameter. Several other Lactifluus species resemble L. volemus, such as L. corrugis, but can be distinguished by differences in distribution, visible morphology, and microscopic characteristics. L. volemus is widely distributed in the Northern Hemisphere, in temperate regions of Eurasia and North America, as well as some subtropical and tropical regions of Asia. A mycorrhizal fungus, its fruit bodies grow on the ground at the base of various species of trees from summer to autumn, either individually or in groups. It is valued as an edible mushroom and is sold in some Asian markets.
Taxonomy The first mention of Lactifluus volemus in the scientific literature was in Carl Linnaeus's 1753 Species Plantarum, under the name Agaricus lactifluus. In 1821, Swedish mycologist Elias Magnus Fries called it Agaricus volemus in his Systema Mycologicum. In this work he proposed a grouping of related species (called a tribus, or tribe) within the genus Agaricus, which he named Galorrheus. Fries later recognised Lactarius as a distinct genus in his 1838 Epicrisis Systematis Mycologici, citing Galorrheus as a synonym. Although Linnaeus had published the species before Fries, Fries's name is sanctioned and thus has nomenclatural priority. In 1871, Paul Kummer raised most of Fries's tribes to generic rank, and so renamed the species Galorrheus volemus. The variety L. volemus var. subrugosus was identified by Charles Horton Peck in 1879, but is now classified as a separate species, L. corrugis. In 1891, Otto Kuntze moved the species into Lactifluus, which was afterwards long considered a synonym of Lactarius but confirmed as a separate genus through molecular phylogenetics in 2008 and subsequent taxonomical rearrangements within the family Russulaceae. Another historical synonym is Lactarius lactifluus, used by Lucien Quélet in 1886, a renaming based on Linnaeus's Agaricus lactifluus. Lactarius wangii, reported by Hua-An Wen and Jian-Zhe Ying to be a new species from China in 2005, was synonymised two years later with L. volemus. The specific epithet "volemus" is derived from the Latin vola, meaning "the hollow of the hand", suggestive of Fries's reference to the large amount of latex "flowing enough to fill the hand". Common names for L. volemus include the weeping milk cap, the tawny milkcap, the orange-brown milky, the voluminous-latex milky, the lactarius orange, the fishy milkcap, and the apricot milk cap. In the West Virginian mountains of the United States, the mushroom is called a "leatherback" or a "bradley". The latter name may originate from its German name Brätling.
Phylogeny
Lactifluus volemus was the type species of the section Dulces in subgenus Lactarius, and is currently classified in Lactifluus section Lactifluus. The group around this L. volemus includes species with a dry cap, abundant latex, and a white or pale cream spore print. Because the closely related L. corrugis has overlapping morphological characters, including similar colouration in the cap and stem, it has been difficult to reliably distinguish between the two species. The difficulty in discerning the two is exacerbated by the fact that both species have several colour forms: Japanese specimens of L. volemus may have a red cap, a yellow cap with a long stem, or a velvet-like surface texture; the caps of L. corrugis may be either red, commonly rust-coloured. In 2005, Japanese researchers clarified the relationships between these two species and others in section Dulces using molecular phylogenetics, and by comparing differences in fatty acid composition, morphology, and taste. The colour variants group phylogenetically into different subclades, suggesting that they might better be considered as "different species, subspecies, or varieties". A 2010 molecular study of L. volemus of northern Thailand found that 79 tested specimens could be divided into 18 distinct phylogenetic species; six of these were described as new species: Lactifluus acicularis, L. crocatus, L. distantifolius, L. longipilus, L. pinguis and L. vitellinus.
Description The fruit body of L. 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 (2–4+1⁄2 in), 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 (1+1⁄2 and 5 in), and which is typically between 1 and 1.5 cm (3⁄8 and 5⁄8 in) 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.
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