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Species Information
Summary: This fungus sometimes grows with a lateral or no stem on pine and other conifers, or sometimes on the ground with a central stem (likely on buried roots). It has light buff to reddish brown, tomentose to bald, two-layered flesh, and a buff to yellowish brown pore surface. Microscopically it has hooked setae projecting from spore bearing surface. For many years this fungus has been known as Inonotus circinatus (Fr.) Gilb. which has been found to be a synonym of Onnia tomentosa. The name used by Ginns(28) for British Columbia is Onnia leporina (Fr.) H. Jahn, which in the online Species Fungorum, accessed April 3, 2018, is a synonym of Inonotus leporinus (Fr.) Gilb. & Ryvarden, Syn. Fung. (Oslo) 6: 328 (1993). Siegel(2) use the name Onnia triquetra (Pers.) Imazeki for California and say that O. leporina appears to be a misapplied name in their area. The description is derived from Gilbertson(1).
Onnia triquetra has been found (as Inonotus circinatus) in BC, WA, OR, ID, AB, AZ, CA, CO, CT, LA, MT, NM, NY, PA, SC, TN, UT, and WY, (Gilbertson).
Cap: up to 18cm wide and 11cm thick, usually with a lateral stem-like attachment or attached without a stem on the butt of dead or living trees, but sometimes on the ground near the base with a central stem, annual; upper surface light buff to reddish brown; tomentose to bald
Flesh: up to 1cm thick, with two layers, an upper spongy layer and a firm corky layer next to the tubes
Pores: 3-4 per mm, angular; buff to yellowish brown; tube layer up to 1cm thick, decurrent, colored as lower layer of flesh, but tubes often whitish inside
Stem: up to 2cm thick, tomentose
Microscopic: spores 5-6.5 x 3-4 microns, elliptic to oval, smooth, inamyloid, acyanophilous, colorless; basidia 4-spored, 18-27 x 6-7 microns, clavate; setae scattered but frequent, 50-80 x 12-20 microns, subulate, mostly hooked, projecting 40-50 microns; context hyphae in upper spongy layer 3-6 microns wide, thin-walled, pale yellowish to colorless in KOH, septate, rarely branched, also some gloeoplerous hyphae 5-7 microns wide, with rounded to slightly clavate tips, filled with a strongly refractive material, context hyphae of lower solid layer 3-5 microns wide, pale yellowish, septate, rarely branched, mostly not incrusted but in some areas with a gummy granular incrustation, trama hyphae 2.5-6 microns, thin-walled, pale yellowish to colorless, septate, with occasional branching, [illustrated septa shown as simple-septate]
Habitat / Range
annual, found on conifers, most commonly Pinus (pine), causing white pocket rot of the heartwood in the roots and butts of living conifers, the rot "characterized by sharply defined empty pockets separated by wood that is firm and apparently undecayed"
Similar Species
Onnia tomentosa fruitbodies are typically found in large numbers (whereas those of ''Inonotus circinatus'' are typically found singly), are generally smaller and thinner and occur on the ground, and microscopically they have straight setae, (Gilbertson), O. tomentosa typically grows under spruce, with cap up to 11cm across, and the setae have straight apices, whereas O. triquetra (as O. leporina) typically grows under pine, with cap up to 18cm across, and the setae have hooked apices, (Ginns(28)).
