Summary:
Much confusion has surrounded this species: Arora(1), Lincoff(2), Bessette(2), and Barron(1) all give Pleurotus ulmarius as a synonym of this species, but the synonymy is incorrect. Redhead in 1986 (Redhead(25)) says Hypsizygus tessellatus is a species 1) that often grows cespitosely, 2) in North America grows on poplar and sugar maple, occasionally on Betula, Ulmus, Abies, and Fagus, 3) has a guttate-marmorate cap when fresh, (Bulliard''s ''tessellatus'' emphasizes the spots, Peck''s ''marmoreus'' the lines between, but the cap is not cracked in a tessellated manner), and 4) has small round to nearly round spores 4-5(6) x 4-5 microns. |Redhead continues that in contrast the species H. ulmarius (Bull.: Fr.) Redhead 1) usually grows solitarily, 2) in North America grows frequently on elm and box elder (Acer negundo), occasionally on Populus and other Acer species, 3) has a smooth not guttate cap when fresh which often becomes areolate-cracked [cracked like dried mud] with age and 4) has larger nearly round to broadly elliptic spores (5)5.5-6(7) x 5-5.5(6) microns. Both species are found in Eurasia. |According to Redhead(1984) in Redhead(39), H. ulmarius is found in North America in areas east of the continental divide and generally central latitudes; H. tessulatus (Bull. ex Fr.) Singer is found from coast to coast and north to the Yukon. |Bessette(2) incorrectly reported Redhead (1986) as saying that Hypsizygus tessulatus (Bulliard: Fr.) Singer is the same fungus as H. ulmarius. |The following description is derived from the Miller(16) field guide (1979) description of Pleurotus elongatipes, except the habitat and microstructures which are from Redhead. The Miller(14) field guide (2006) description of Hypsizygus tessulatus is very close to this one and appears to be based on it. |(Note that Hypsizygus tessellatus refers to the same species - MycoBank, accessed May 19, 2020 give as a synonym Agaricus tessellatus Bull., Histoire des champignons de la France. I: pl. 513 (1791) and gives as the sanctioning name Agaricus tessulatus Bull., Histoire des champignons de la France. I: pl. 513 (1791). Redhead(25) used the name Hypsizygus tessellatus in his 1986 discussion of the species, but the name is little used in recent years.)

Gills:
"adnexed (notched)", with a thin line on the upper stem, "subdistant, broad, veined"; "buff to pinkish buff"

Stem:
4-22cm x 0.4-2cm, nearly equal or gradually narrowing toward base, often curved or bent; white; smooth except near the top where there is white down, and the base, which has white stiff hairs

Veil:
absent

Microscopic spores:
spores 4-5(6) x 4-4.5 um, round to nearly round, smooth

Notes:
Collections of Hypsizygus tessulatus from BC are deposited at University of British Columbia, and collections from WA and AK are deposited at the University of Washington.

EDIBILITY

yes

Synonyms and Alternate Names:
Hypsizygus marmoreus (Peck) H.E. Bigelow