The North American Species of Pholiota

43. Pholiota albo-olivascens sp. nov.

Illustrations: Text figs. 135-138.

Pileus (1) 2-3 (5) cm latus, convexus, se extendens, viscidus, hygrophanus, albus siccatus, "Isabella-color" humidus, appressus sericus et similis pelli villosae, margine striatus madidus. Caro tenuis, denum alba, odore et gustu mitis. Lamellae adnatae deinde adnatae-decurrentes, albae deinde "Dresden brown" demum "snuff-brown," medio-latae, confertae; marginibus albo-denticulatae. Stipes 3-5 cm longus, 2-4 mm crassus, albidae deinde furvae, sericeae, aequales. Velum arachnoideum, album, permanentem demum fugacem annulum ostendens. Sporae 6-9 x 3.8-4.5 µ, ellipsoideae demum ovoideae in fronte, parvum inaequilaterales in imagine oblique, leves, truncatae. Pleurocystidia 24-46 x 6-8 µ clavata demum ventricosa, appendiculata; cheilocystidia 30-37 x 4-6 µ, obclavata, fusoidea. Cuticula gelatinosa. Fibulae non inventae. Specimen typicum in Herb. Univ. Tenn. conservatum est; legit in Cades Cove, Blount County, Tennessee, 16 May 1953, Hesler 20814.

Pileus (1) 2-3 (5) cm broad, convex, expanding, at times wavy, viscid, hygrophanous, white when dry, olive-yellow moist ("Isabella-color"), fading from disc outward, surface appearing glabrous but actually appressed-silky and plush like under a lens, margin even when dry, striate when wet. Context rather fragile, thin, white, darker when wet; odor and taste mild.

Lamellae adnate to adnate-decurrent, at first white then dark yellow-brown ("Dresden brown" to "snuff-brown"), medium broad, close, reaching margin of pileus, edges white-denticulate.

Stipe 3-5 cm long, 2-4 mm thick, whitish, dingy in age, dry, silky, striate, equal, usually curved, spongy then hollow. Veil delicate, webby, white, forming an apical, persistent to subfugaceous annulus, often brownish from spores.

Spores 6-7.5 x 4-4.5 µ (6-9 x 3.8-4.5 µ in some caps), smooth; wall 0.4 µ thick (±), apex obscurely truncate from a small apical pore; in face view ovate to elliptic, in profile obscurely inequilateral, occasionally a spore seen with a lateral bump; tawny in KOH, slightly more cinnamon in Melzer's.

Basidia 4-spored, 18-23 (26) x 5-7 µ, hyaline in KOH and pale yellow in Melzer's reagent. Pleurocystidia abundant 25-46 x 6-9 µ, clavate-rostrate to mucronate, the neck often as long or longer than the enlarged portion in old specimens, walls thin, hyaline, smooth, content homogeneous, cystidium yellowish and with homogeneous content in Melzer's reagent. Cheilocystidia 28-44 x 4-9 µ, ventricose near base and with a long neck 3-4 µ wide in some, and ending in a subacute apex, wall in neck usually flexuous, thin, hyaline in KOH or Melzer's. Caulocystidia 33-58 x 6-11 µ, clavate to obscurely fusoid-ventricose because of the irregular wavy walls and variously spaced protrusions, some with an acute apex and the neck back of it about 2 µ diam., walls thin and hyaline and smooth.

Gill trama of hyphae subparallel interwoven, cells often short and up to 16 µ diam., walls thin and hyaline in KOH to slightly brownish-ochraceous, yellowish in Melzer's reagent; subhymenium indistinct at first, finally cellular in age, not gelatinous. Pileus trama with a thin cutis of somewhat gelatinous hyphae tubular and 2.5-4 µ diam., hyaline and appressed; hypodermium of greatly inflated hyphae (cells 10-20 µ) hyaline in KOH and walls about 1 µ thick with the middle lamella evident in mounts revived in KOH. Context hyphae floccose-interwoven, hyaline in KOH and pale yellow in Melzer's, 8-15 µ diam. Hyphae of stipe apex hyaline in KOH, walls smooth. Clamp connections present.

Habit, Habitat, and Distribution: On hardwood logs and chips, Tennessee, May, Hesler 20814, type; Cades Cove, Great Smoky Mts. Nat'l. Park, May 16, 1953.

Observations: This is a most distinctive species by reason of the broad close gills, abundant pleurocystidia, pale colors, and lack of a positive KOH reaction in the hyphae of the upper part of the stipe. In this genus this feature is almost always correlated with the absence of darkening in the stipe as the latter ages. P. albo-olivascens appears to be most closely related to P. veris.

One of the interesting features of our study of this species is that very rarely one can find a "pleurocystidium" on the apex of which is a single spore and the upper part of the sterigmata for a distance of 10-15 µ back from the spore is seen to have a colored wall thickened and resembling the spore wall and is continuous with the latter. We cannot see how a spore attached in this manner could ever be discharged in the manner of the spores borne in the normal way on 4-spored basidia with very fine hyaline sterigmata. To us it indicates that the change from active spore discharge to a state of no spore discharge by the basidium can occur in a single basidiocarp. This may have some interest to those studying the relationships of Pholiota to gastromycetous fungi. Several points need to be clarified in regard to this feature as follows: The cells producing the spores appear to be cystidia, not basidia, as far as their shape is concerned. What is their nuclear history? Thousands of cystidia without spores are found to one with a spore, so it is not proper to classify all the pleurocystidia as one-spored basidia. The homology, however, seems obvious. It is interesting to note that this same sort of modification of the sterigmata-becoming thick-walled and continuous with the spore wall, has been noted for other rusty-brown spored agarics by Heim and others, and is not infrequent in the form-order "Agaricogastrales."