Pileus 10-15 mm in diameter, convex to broadly convex, with or without a broad low umbo; surface subviscid to tacky, radially translucent striate to undulate, glabrous; margin incurved, irregular to even; disc colored "Orange Rufous" to "Sanford Brown"; margin colored "Orange-Buff" to "Light Orange-Yellow." Lamellae adnexed to slightly adnate in age, distant, thin, up to 5 mm broad; edges even, not marginate; lamellulae in 3-4 tiers, not forked; color "Pale Yellow- Orange," not staining. Stipe 50-65 mm long, 1-2 mm wide, terete, equal above, radicating, tapering gradually to a firm point below, conspicuously undulating in a corkscrew fashion on the lower half (Fig. 3), and having the appearance of a criniform pseudorhizae of a Phaeocollybia (Phaeocollybia attenuata group); moist to dry but not viscid, surface pruinose to pubescent, with a slight sheen beneath the pruinosity, apically coloured "Pale Yellow-Orange" to "Orange-Buff," nearly black or blackish brown for most of its length except for a pallid yellowish hoar at the very base. Odor and taste not distinctive.
Pileus tissues (Figs. 4, 6, and 8) consisting of three distinctive layers: (1) a relatively thin suprapellis 22-36 µm thick (in Melzer's), (2) an exceedingly thick mediopellis, 325335 µm deep, and (3) a relatively thin, tough, true context, 85-95 µm deep.
(1) Suprapellis palely pigmented yellowish brown, consisting of two cell categories (Fig. 9): (A) a palisade-like layer of well-spaced, erect to somewhat collapsed, more or less short clavate, pedicellate-clavate, mucronate-clavate, eccentrically rostrate-clavate, or occasional short lageniform end cells, all embedded in a gel, each in the range of 9-20(-30) µm long, and 4.5-8 µm wide where swollen, with thin hyaline to faintly melleous colored walls and frequently internally guttulate and (B) scattered 25-61 µm long, 6.5-13.5 µm wide where swollen projecting pileocystidia, lageniform with a fusoid base, either short stalked or pedicellate with a narrow stalk and with apices projecting 13-27 µm above the gel; walls tending to be more heavily brownish pigmented as viewed in 2% KOH solution, slightly thicker and more readily taking up Congo Red stain than the palisade cells.
(2) Mediopellis a very conspicuous, thick, hyaline, gelatinous layer replacing the context as the main structural tissue; 1- to 3 µm-diameter hyphae distantly spaced in the gel, with conspicuous clamp connections and a sheath of slightly more refractive gel close to their otherwise smooth thin walls. An indistinct subpellis composed of slightly denser tissue than that of the context is vaguely discernable at the transition zone.
(3) Context a thin layer resembling a subhymenial layer because of its thinness and proximity to the hymenium and the tissue's extension into the lamellae; hyphae a dense mixture of thin-walled often frequently branched and interwoven, noninflated cells, mostly highly internally refractive and oleiferous, hence very opaque, silvery to golden, and oily.
Lamellar trama tissue similar to the context, i.e., dense, oily. Subhymenium a thin zone of more densely branched hyphae with fewer oleiferous elements. Basidia 29-31 x 4.56.5 µm, clavate, hyaline, clamped, 4-spored (Fig. 12); sterigmata 2.5-3.0 µm long. Pleurocystidia not seen. Cheilocystidia 35-41 x 7-8 µm, forming a dense sterile lamellar margin; size, shape and wall staining similar to that of pileocystidia, hyaline, lageniform, fusoid-ventricose, with or without a pedicellate base (Fig. 10).
Basidiospores 5.5-7.5 x 4.5-6.0 µm (mean of 10 spores = 6.52 x 4.85 µm, Q = 1.34), broadly ellipsoid to slightly ovoid, slightly obovoid, or very broadly lacrymoid, smooth, thin walled, hyaline, nonamyloid, with a prominent apiculus (Fig. 13).
Stipitipellis a layer of parallel 3- to 4 µm-diameter filamentous hyphae at the stipe apex, honey colored to hyaline, with subgelatinized walls and interhyphal spaces, darkening lower on the stipe to dark reddish blackish brown and becoming brittle, giving rise to solitary to clustered caulocystidia or cystidioid branches. Caulocystidia 22-50 x 4.5-12 µm, typically lageniform, some narrow, some broad, a few subcapitate, with broad or narrow bases (Fig. 11), initially hyaline but darkening like the stipe, with slightly thickened walls. Stipe inner cortical hyphae on lower stipe contrasting sharply with the superficial cortical hyphae in color, 3.5-11.0 µm in diameter, honey colored, with subgelatinized walls; mixed with scattered refractive oleiferous hyphae. Hyphae of basal pruina actually elongated cystidioid hair ends, 2.3-2.7 µm in diameter, with thickened reddish brown walls.

CULTURES: Self-cross: When 12 single-basidiospore isolates were paired in all combinations, a tetrapolar mating system was revealed (Table 1). Isolates 3*, 9, 14 = A₁B ₁;1*, 17, 18 = A₂B₂; 2*, 4, 5, 12, 16, 17 = A₁B₂; A₂B ₁ was unrepresented in the sample. Only isolates 3 and 17 gave consistent positive readings where expected. Single-basidiospore isolates grew extremely slowly and weakly, with colonies taking over 3 months to make contact and over 5 months to form a wellformed contact zone. Exemplars of F. stratosa tested negative against all other available Flammulina exemplars as part of a larger study that will be detailed elsewhere.
CULTURE MORPHOLOGY: Colonies were characterized by the following. (1) Narrow or torulose appressed to submerged hyphae, almost empty except for scattered pale tan guttules. (2) Desiccated aerial hyphae. (3) Conidia produced in two ways: (A) within 0.5- to 1.5-mm-diameter dark brown to brownish black balls covered with a leathery rind (textura intricata) with caulocystidia-like structures covering the entire surface (once the rind was ruptured, the firm but moist mass of conidia could be smeared across the agar) and (B) in somewhat slimy heads on aerial conidiophores. While the mode of conidial formation is unknown, groups of conidia were observed to resemble "hands of bananas", similar to that seen when conidia are formed sympodially. Conidia ellipsoidal, smooth, tan (brown in mass). (4) In most pairings, the agar turned brown with slight pinkish cast, either limited to the contact zone or starting there. (5) Color of contact zones of all compatible pairings remained white to very pale (unchanged from color of agar), often with no discernable seam in the contact zone. It should be noted that although putatively incompatible pairings were also white, clamp connections were so difficult to see in all pairings that some pairings scored as incompatible may actually have been compatible.