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Albatrellus subrubescens is a terrestrial polypore fungus. The fruit bodies of the fungus have whitish to pale buff-colored caps that can reach up to 14.5 cm (5.7 in) in diameter, and stems up to 7 cm (2.8 in) long and 2 cm (0.8 in) thick. On the underside of the caps are light yellow to pale greenish yellow tiny pores, the site of spore production. When the fruit bodies are fresh, the cap and pores stain yellow where exposed, handled, or bruised. The mushroom is found in North America, Europe and China, where it grows on the ground in deciduous or mixed woods, usually in association with pine trees. It is closely related, and physically similar, to the more common Albatrellus ovinus, from which it may be distinguished macroscopically by differences in bruising colors, and microscopically by the amyloid (staining bluish-black to black with Melzer's reagent) walls of the spores. The fruit bodies contain a chemical named scutigeral that has antibiotic and pharmacological activity. The fungus is inedible.
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| Phylogeny and relationships of A. subrubescens and selected related species based on ribosomal DNA sequences.[2] |
The species was first described by American mycologist William Murrill, who found it in Florida in 1940 and named it Scutiger subrubescens;[3] in 1947 he transferred it to the genus Polyporus.[4] Josiah Lincoln Lowe later identified the species as Albatrellus confluens.[5] In 1965, Zdeněk Pouzar collected samples from Czechoslovakia, and described it as a new species (Albatrellus similis), not aware of the similarity to Murrill's Florida specimens.[6] Further study revealed that A. similis was identical to Murrill's Scutiger subrubescens, and the epithet was transferred to Albatrellus.[7] In 1974, Pouzar recognized that Lowe's Albatrellus confluens was a species distinct from A. subrubescens.[8] The specific epithet subrubescens is derived from the Latin words sub ("under") and rubescens ("to grow red").[9]
Four Albatrellus species were included in a large-scale phylogenetic analysis of the Russulales order published in 2003. Based on their ribosomal DNA sequences, the four form a clade, or monophyletic group (that is, they derived from a single ancestor). Of the four tested species, A. ovinus was most closely related to A. subrubescens. The polypore Wrightoporia lenta (type species of the genus Wrightoporia) occurred on a single branch basal to the albatrellus clade, implying that it was an earlier ancestor from which the Albatrellus species were derived.[2]
The cap of A. subrubescens is between 6 to 14.5 cm (2.4 to 5.7 in) in diameter, with a central, eccentric, or rarely lateral stem. Initially, the cap is convex with an involute margin, flattening out with age. The cap margin may be folded or flat. The cap surface in young specimens is smooth but soon forms appressed scale-like spots, which may transform into scales in age.In young specimens the cap margin is white, and brownish violet in the center and on the scale-like spots, later becoming orange-brownish or ochraceous brown. Some specimens may be covered with blackish-gray to purple-gray fibrils.[10] The cap discolors yellow to orange when bruised. The stem is 1.6 to 7 cm (0.6 to 2.8 in) long and 1 to 2 cm (0.4 to 0.8 in) thick, cylindrical, irregular, and the base of the stem may be somewhat pointed, or bulbous. Initially white, the stem develops orange/violet spots and later brownish orange spots; in old specimens the stem may be brownish brick red. The tubes on the pore surface (underside of the cap) are about 2.5–3 mm long and decurrent in attachment; the pores are small (about 2–3 per millimeter), initially greenish-white, but later dark brown. Dried specimens can have pores that are tinted green.[11] The fruit bodies have a "faintly fragrant, pleasant" odor, and lack a distinctive taste.[10] They are considered inedible.[12]
In deposit, the spores are white.[12] The spores are 3.4–4.7 by 2.2–3.4 µm, ellipsoid to ovoid in shape, and amyloid. Most have a single large oil drop. The spore-bearing cells (the basidia) are club-shaped, 12–16 µm long by 5.7–7.7 µm thick, with four thin, slightly curved sterigmata that are 3.4–4.3 µm long.[11] The hyphal system is monomitic, meaning that there are only thin-walled skeletal hyphae present. These hyphae are typically 6–17 µm, with thin walls (up to 1 µm thick), and hyaline (translucent). Although they are nonamyloid (not absorbing iodine when stained with Melzer's reagent), some hyphae have internal masses that are colored pale bluish-gray to black, which makes them appear collectively grayish-black under the microscope.[10]
Albatrellus ovinus is similar in appearance, however, A. subrubescens often has a violet color. Microscopically, the spores of A. subrubescens are amyloid, while the ones of A. ovinus are not,[13] and A. ovinus has smaller spores, typically 3.8–4.6 by 3.3–3.5 µm.[7] In general, A. subrubescens can be distinguished from other Albatrellus species by its white cap that becomes orange when bruised, its simple-septate hyphae, small amyloid spores, and habitat under Pinus.[14] Other closely related species include A. cantharellus and A. tianschanicus, which differ from A. subrubescens by the hairy scales on the cap surface, and because the scales of A. subrubescens are not much darker then the area between the scales.[7] A. confluens has caps that are colored pinkish-buff to pale orange, and white flesh that dries to a pinkish-buff; it has a taste that is bitter, or like cabbage. The spores of A. confluens are weakly amyloid.[12]
Specimens of A. subrubescens are usually solitary, but sometimes several (usually between two and eight) fruit bodies are stuck together by the stem bases or on the sides of their caps.[10] It is strictly terrestrial, not found on wood. The species has been reported from a variety of locations in central Europe, North America,[15][16] In western North America, its distribution includes Arizona, Alberta, California, Northwest Territories, and Washington;[10] The distribution extends south to Mexico (Chiapas).[17][18] It is also found in the Gulf Coast region, from Florida to Texas.[12] In Asia, it has been collected from China (Yunnan and Tibet),[14] and Japan (as A. cantharellus).[11] It prefers to grow in pine woods, but has occasionally been associated with silver fir. Ginns, relating a personal communication with David Arora, writes that Arora "found many clumps of basidiomes in a half hectare area covered mainly by a mixture of Pinus attenuata, manzanita, huckleberry, and a few scattered mandrones."[10]
Albatrellus subrubescens contains the bioactive compound scutigeral, which has antibiotic activity. This chemical is also found in the related species A. ovinus.[19] Scutigeral interacts selectively to the dopamine receptor D1 subfamily (the most abundant dopamine receptor in the central nervous system, regulating neuronal growth and development, mediating some behavioral responses).[20] A 1999 publication suggested that scutigeral had agonistic activity at vanilloid receptors (a receptor found on sensory nerves throughout the human body), specifically, that it influenced the uptake of calcium in rat dorsal root ganglion neurons.[21] However, a 2003 study failed to find any such pharmacological activity.[22]