Fleshy Fungi of New Brunswick >> Clitopilus hobsonii

Clitopilus hobsonii (Berk.) P.D. Orton

Gregarious (many) on a rotten and blackened agaric attached to a hardwood log, possibly also associated with a moribund member of the Xylariaceae, growing in an annually flooded area dominated by Acer rubrum, Fraxinus sp., Abies balsamea and Picea rubens – Wilson Brook Protected Natural Area, New Brunswick (28-07-20/02).

Pileus broadly convex, white, developing some yellowish colours in age, densely tomentose at first but later nearly glabrous, striate, 6-15 mm in diameter. Stipe lacking, the pileal attachment is either lateral or slightly dimidiate. Lamellae white, close, not marginate. Flesh white, with a nondescript mushroom odour and taste or slightly bitter.

Basidiospores very pale yellowish pink in spore print, ellipsoidal, with approximately 8 longitudinal ridges, with ridges only slighly evident in profile but more easily seen in end view, without iodine reactions, 6.5-9.1 x 4.0-4.8 µm, Q = 1.56-1.91 (average[50]: 7.6 x 4.4 µm, Q = 1.73). Hymenial cystidia not seen. Basidia 4-spored, clavate, without a basal clamp connection. Pileipellis a thick tomentose trichoderm above the much thinner pileus trama. Clamp connections not seen on any hyphae.

Clitopilus hobsonii is small pleurotoid fungus easily mistaken for a species of Crepidotus or Cheimonophyllum. Unlike species of these two genera, with basidiospores that are brown in the former and white in the latter, species of Clitopilus produce a pale pink or yellowish pink spore print. These basidiospores are further distiguished microscopically by their low longitudinal ridges, giving them an obscurely octagonal shape when viewed on end. The ridges are not at all evident when mounted in KOH, but can be seen as shadowy ridges running the length of the spore.

Collection 28-07-20/02 differs from other reported collections of this species in having basidiospores less than 5μm in diameter. In addition, C. hobsonii is usually described as having flesh with a farinaceous (mealy) odour while this collection was described as essentially odourless.

Photograph: D. Malloch (28-07-20/02).