Albatrellus subrubescens

Albatrellus subrubescens is a species of polypore fungus in the family Albatrellaceae. The fruit bodies (mushrooms) 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 tiny light yellow to pale greenish-yellow pores, the site of spore production. When the fruit bodies are fresh, the cap and pores stain yellow where exposed, handled, or bruised.
The species is found in Asia, Europe, and North America, 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 the color when bruised, and microscopically by the amyloid (staining bluish-black to black with Melzer's reagent) walls of the spores. The fruit bodies of A. subrubescens contain scutigeral, a bioactive chemical that has antibiotic activity. A. subrubescens mushrooms are mildly poisonous, and consuming them will result in a short-term gastrointestinal illness.
==Taxonomy and phylogeny==
The species was first described as Scutiger subrubescens by American mycologist William Murrill in 1940, based on collections that he found growing under oak near Gainesville, Florida, in November 1938. In 1947 he transferred it to the genus Polyporus. Josiah Lincoln Lowe examined Murrill's type material and thought that it did not differ from Albatrellus confluens. In 1965, Zdeněk Pouzar made collections from Bohemia (now the Czech Republic), and described it as a new species (Albatrellus similis), unaware of the similarity to Murrill's Florida specimens. Further study revealed that A. similis was identical to Murrill's Scutiger subrubescens, and Pouzar transferred the latter epithet to Albatrellus. In 1974, Pouzar recognized that Lowe's species Albatrellus confluens was distinct from A. subrubescens. The specific epithet subrubescens, "tinted reddish", is derived from the Latin words sub ("less than") and rubescens ("growing red").
Four Albatrellus species were included in a large-scale phylogenetic analysis of the order Russulales 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 shared with the Albatrellus species a common ancestor from which both were descended. In a more recent (2010) molecular analysis by Canadian mycologist Serge Audet aimed at clarifying relationships among species formerly placed in Scutiger, A. subrubescens grouped in a clade with A. ovinus and A. citrinus. According to Audet, these species, in addition to A. avellaneus and A. piceiphilus, are the constituents of an Albatrellus with limits defined by molecular genetics. Other Albatrellus species were transferred to segregate genera: A. fletti and A. confluens to Albatrellopsis; A. caeruleoporus and A. yasudae to Neoalbatrellus; A. pes-caprae and A. ellisii to an amended Scutiger.
==Description==
The cap of A. subrubescens is between in diameter, with a central, eccentric (away from the center), or rarely lateral (attached to the edge of cap) 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. Initially, the cap has white margins and a brownish-violet center with scale-like spots; the center later becomes orange-brownish or ochraceous brown. According to Canadian mycologist James Ginns, who described North American Albatrellus species in 1997, some North American specimens may be covered with blackish-gray to purple-gray fibrils, but this characteristic is not seen in European collections. The cap discolors yellowish 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 its base 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, measuring about 2–3 per millimeter. They are initially greenish-white, but later turn dark brown; dried specimens can have pores that are tinted green. Fruit bodies have a "faintly fragrant, pleasant" odor; in his original report on the species, Murrill noted that specimens left to dry in an oven developed a strong odor of burnt sugar. The taste of the mushroom has been described variously as indistinct, or "distinctly bitter". The type material was noted by Murrill to taste bitter, an observation later corroborated by Pouzar with European collections. A. subrubescens mushrooms are mildly toxic: consumption causes a gastrointestinal illness that usually subsides one to four hours after ingestion.
In deposit, the spores are white.