Pinecone mushroom

Appearance

The fruit body of "A. vulgare" is fibrous when fresh and becomes stiff when dry. It is small species rarely exceeding 55 mm in height, with a cap usually smaller than an adult's fingernails: 0.5 to 2 cm —although it has been known to reach up to 4 cm.

"Auriscalpium vulgare" usually has a single stem, but occasionally several stems arise from a thick common base. It attaches to the side of the cap and is cylindrical or slightly flattened with a bulbous base. Its surface is covered with hairy fibers, and its mature color is a dark chestnut brown. The cap is semicircular or kidney-shaped, flat on the lower surface and rounded on the top. The surface is at first much like the stem: covered with bristles and dark chestnut brown. However, it becomes smooth with maturity and can darken to the point of being almost black. The cap margin is usually buff to light brown–roughly the same color as the spines and lighter in color than the center. It becomes rolled inward and often wavy in maturity. The spines on the underside of the cap are a few millimeters long and cylindrical down to their sharp tips. White to light brown when young, they later become covered with a white spore mass and then turn an ashy gray. Occasionally, fruit bodies are produced that lack a cap entirel

The cap flesh is composed of two distinct layers: a thin, compact, black-brown and hairy upper layer, and a thick, soft, white to light brown lower layer that is made of thin, thread-like filaments arranged in a roughly parallel fashion. The stem is similarly divided, with a thin, dark and hairy cortical layer covered by hairs, which encircles inner ochre-colored flesh. A drop of potassium hydroxide applied to the surface of the mushroom will cause it to instantly stain black.

The hyphae of basidiomycetous fungi are partitioned by cross-walls called septa, and these septa have pores that permit the passage of cytoplasm or protoplasm between adjacent hyphal compartments. In an effort to determine ultrastructural characters useful for systematic and phylogenetic analyses of the Agaricomycotina, Gail Celio and colleagues used electron microscopy to examine both the structure of the septal pore, and nuclear division in "A. vulgare". They determined that septa found in hyphae of the hymenium have bell-shaped pore "caps" with multiple perforations. Each cap extends along the length of the septum, along with a zone surrounding the pore that is free of organelles. Due to the scarcity of similar data from other Agaricomycotina species, it is unknown whether the extended septal pore cap margins of "A. vulgare" are phylogenetically informative. Regarding nuclear division, the process of metaphase I of meiosis is similar to the metaphase of mitosis. Spherical spindle pole bodies containing electron-opaque inclusions are set within gaps on opposite ends of the nuclear membrane. This membrane has occasional gaps but is largely continuous. Fragments of endoplasmic reticulum occur near the spindle pole bodies, but do not form a cap.

Distribution

"Auriscalpium vulgare" is a saprobic species. Its mushrooms grow solitary or clustered on fallen pine cones, especially those that are fully or partially buried. It typically favors Scots Pine, but has also been reported on spruce cones, and in California grows primarily on Douglas-fir cones. One author noted finding the mushroom on spruce needles on top of squirrel dens where cone bracts were present in the forest floor. In a study conducted in the Laojun Mountain region of Yunnan Province, China, "A. vulgare" was found to be one of the most dominant species collected from mixed forest at an altitude of 2,600–3,000 m. A study on the effect of slash and burn practices in northeast India showed that the fungus prefers to fruit on burned cones of the Khasi Pine, and that the number of fruit bodies on unburned cones increases with cone girth.

Habitat

"Auriscalpium vulgare" is a saprobic species. Its mushrooms grow solitary or clustered on fallen pine cones, especially those that are fully or partially buried. It typically favors Scots Pine, but has also been reported on spruce cones, and in California grows primarily on Douglas-fir cones. One author noted finding the mushroom on spruce needles on top of squirrel dens where cone bracts were present in the forest floor. In a study conducted in the Laojun Mountain region of Yunnan Province, China, "A. vulgare" was found to be one of the most dominant species collected from mixed forest at an altitude of 2,600–3,000 m. A study on the effect of slash and burn practices in northeast India showed that the fungus prefers to fruit on burned cones of the Khasi Pine, and that the number of fruit bodies on unburned cones increases with cone girth.

The fungus is widely distributed in Europe, Central and North America, temperate Asia, and Turkey. In North America, its range extends from Canada to the Trans-Mexican Volcanic Belt south of Mexico City. The mushroom is common, appearing in the summer and autumn, although it is easily overlooked because of its small size and nondescript coloration. "A. vulgare" is the only representative of its genus in temperate areas of the Northern Hemisphere.

Evolution

The species was first described in the scientific literature by Carl Linnaeus under the name "Hydnum auriscalpium" in his 1753 "Species Plantarum". Linnaeus placed three other tooth fungi in the genus "Hydnum": "H. imbricatum", "H. repandum", and "H. tomentosum". In 1821 Samuel Frederick Gray considered "H. auriscalpium" to be sufficiently distinct from the other "Hydnum" species to warrant the creation of a new genus, "Auriscalpium", to contain it. In the process, its name was changed to "Auriscalpium vulgare".

Otto Kuntze and Howard James Banker later independently sought to restore Linnaeus' species name, but the resulting combination is a tautonym and disallowed under the rules for botanical nomenclature, and these combinations are therefore no longer validly published. Other names given to the fungus and now considered synonyms include "Hydnum fechtneri", named by Josef Velenovský in 1922, and later combinations based on this name. "A. vulgare" is the type species of the widely distributed genus of eight species that it belongs to.
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| style="text-align: left; font-size: 88%; width: 248px; border: 0; padding: 0;" | Cladogram showing the phylogeny of "A. vulgare" and other Russulales species based on rDNA sequences.
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Despite vast differences in appearance and morphology, "A. vulgare" is related to such varied taxa as the gilled fungi of "Lentinus", the poroid genus "Albatrellus", the coral-like "Clavicorona", and fellow tooth fungus "Hericium". The relationship of all of these taxa—members of the Auriscalpiaceae family of the order Russulales—has been demonstrated through molecular phylogenetics.

"Auriscalpium vulgare" is commonly known as the "pinecone mushroom", the "cone tooth", "pine cone tooth", or the "ear-pick fungus". Gray called it the "common earpick-stool"; it was also referred to as the "fir-cone Hydnum", when it was still considered to be a member of that genus. The specific epithet "vulgare" means "common". The generic name "Auriscalpium" is Latin for "ear pick" and refers to a small, scoop-shaped instrument used to remove foreign matter from the ear.

Uses

The mushroom, which has no distinct taste or odor, is generally considered inedible because of its toughness and diminutive size. An 1887 textbook noted, however, that it was "commonly eaten in France and Italy".Spore deposits are white. Viewed under a light microscope, the spores appear hyaline, covered with minute wart-like bumps, and are spherical or nearly so, with dimensions of 4.6–5.5 by 4–5 µm. They are amyloid and cyanophilous. The basidia are four-spored with basal clamps, and measure 15–24 by 3–4 µm, and sterigmata are swollen at the base and roughly 3 µm long. The hyphal system is dimitic, comprising both generative and skeletal hyphae. The thin-walled generative hyphae are hyaline, and have clamp connections; the thick-walled skeletal hyphae are thicker overall and lack such connections. The cortex is made of parallel unbranched generative hyphae that are brown, thick-walled, clumped together, and frequently clamped. The internal flesh is made of interwoven generative and skeletal hyphae. Gloeoplerous hyphae are also present, protruding into the hymenium as club-like or sharp-pointed gloeocystidia.

Cultural

"Auriscalpium vulgare" can be grown in pure culture on agar-containing plates supplemented with nutrients. The colonies that grow are white to pale cream, and cover the agar surface within six weeks from the initial inoculation. The mycelium is made of bent-over hyphae, without any aerial hyphae. Typically, two indistinct zones develop at about 6 mm and 15 mm from the initial inoculum spot, with each zone roughly 4 mm wide. The zones appear somewhat lighter in color because the hyphae are more closely packed and form crystalline substances that deposit into the agar.

The mature mycelium consists of thin-walled, densely packed hyphae that are 1.5–3.2 µm in diameter. They are often gnarled or somewhat spiral, and frequently branched at an angle of about 45°, with a clamp at the base of the branch. They contain amorphous granules that appear refractive when viewed under phase contrast microscopy, and their walls are often encrusted with tiny granules. Gloeocystidia are common; they measure 50–85 by 6.5–8.5 µm, and are club-shaped, thin-walled, and often have one or two lobes with rounded tips. Containing foamy and pale yellow contents, they are a refractive yellow color under phase contrast. Initially they are erect but they soon fall under their own weight to lie on the agar surface. Crystalline deposits are abundant as small, randomly scattered plate-like or star-like crystals.

Fruiting begins about six weeks after the initial inoculation on the agar plate, but only when portions of fruit bodies are used as the inoculum to initiate growth; the use of mycelium as the inoculum precludes subsequent fruiting. Mature fruit bodies grow very close to the initial site of inoculation—within 3 mm—and take about 60 days to mature after they first start to form.