Summary:
The Pleurotus ostreatus complex is distinguished by smooth whitish to grayish to brownish caps with a shelf-like habit, soft thick flesh, whitish gills, and a whitish to lilac spore deposit. Vilgalys(4) have divided the complex in North America into Pleurotus ostreatus (Fr.) P. Kumm., Pleurotus pulmonarius (Fr.) Quel., and Pleurotus populinus O. Hilber & O.K. Miller, and this description is derived from theirs for Pleurotus ostreatus except where indicated. Other features of Pleurotus ostreatus in particular are relatively large, spathulate, scallop-shaped, or mussel-shaped caps, close to crowded gills, lilac to lilac-gray or light purplish vinaceous spore deposit, and spores 7.5-9.5 x 3.2-4 microns. Thorn(3) have shown that this species as well as other Pleurotus and Hohenbuehelia species attack and consume nematodes [roundworms]. The P. ostreatus complex is common in the Pacific Northwest.

Cap:
(4)6-15(25)cm wide, convex, spathulate, scallop-shaped to mussel-shaped, margin inrolled becoming nearly flat when old and only slightly inrolled; whitish, yellow, pale yellow to grayish yellow, light tan to dark brown, also drab, light cinnamon drab, cinnamon drab, to light drab near margin, with some caps mostly pale cinnamon-pink; moist when young but never viscid, soon dry; finely white pubescent [downy] to pubescent over the lateral point of attachment to stem, smooth over the rest of the surface

Flesh:
up to 1cm or 2cm thick, firm, somewhat fibrous, solid; white

Gills:
adnate to mostly decurrent, close to crowded, broad, 0.5-1.5cm, with two tiers of subgills, sometimes forming a reticulum [network] near the point of attachment; dull whitish to pale pinkish buff; edge smooth at first, becoming eroded when old

Stem:
(0.5)1-3cm x 0.3-2(3)cm, laterally attached, stocky, nearly equal; dry, white pubescent to strigose at base

Odor:
"pleasant and anise-like, becoming fungoid and unpleasant in age"

Taste:
"mild and pleasant in fresh specimens"

Microscopic spores:
spores 7.5-9.5 x 3.2-4 microns, narrowly elliptic, [presumably smooth], inamyloid, colorless, thin-walled, with a small apiculus; basidia 4-spored, 24-36 x 5-7 microns, narrowly clavate, thin-walled, inamyloid, colorless; cheilocystidia and pleurocystidia infrequent to numerous, most often on gill edge, 14-30 x 3.5-8 microns, clavate-capitate, colorless, thin-walled; clamp connections present in all tissues

Spore deposit:
lilac to lilac-gray, to light purplish vinaceous

Notes:
Collections used by Vilgalys(4) from the Pacific Northwest are P. pulmonarius and P. populinus. Collections of Pleurotus ostreatus used in the Vilgalys(4) analysis are from ON, AL, AR, AZ, CA, DC, FL, GA, IL, MD, MN, MS, NC, NJ, NY, PA, TN, VA, WI, WV, Czechoslovakia, France and Germany. The Pleurotus ostreatus group in the Pacific Northwest includes lilac spored specimens over 15cm wide, at least in BC. DNA from a collection from WA on cottonwood matched with the Pleurotus ostreatus epitype designated in Petersen(30) in 1996. UNITE shows that there are 562 sequences around the world that match the type <0.5%, and 1 specimen was from Canada and 14 are from the US, but they do not appear to say where they were found. The WA specimen is a bit more than .5% different from the type, but that''s only 2bp and 2 indels in ITS1 and 1bp and maybe 0 or 1 indel in ITS2. It''s by far the closest species match. (D. Miller, pers. comm.).

EDIBILITY

delicious, douse in water to remove beetles between gills, remove stems, and check for white grubs (Arora for P. ostreatus complex), adverse reaction from combination with alcohol has been reported with oyster mushrooms (Benjamin)