The genus Subulicystidium is characterized by subulate (tapering to a point) cystidia with rectangular crystals that encircle the cystidia in rows or spirals. And poking out of the top of each cystidium is a hypha, which runs through the center of the barb-like structure. Who knows the adaptive function of these strange microscopic structures, but to me they look like they are for defensive purposes, perhaps against the many animals that graze on crusts. I don't think they stand much of a chance against a snail's radula, though.
According to Ordynets et al. (2018), this specimen matches well with Subulicystidium brachysporum sensu Boidin and Gills (1988).
Ecology: Growing on the exposed wood of a fallen Salix (willow) in early summer, apparently with a global distribution.
Basidiocarp: White, effused, resupinate basidioma with a smooth hymenophore.
Spore print: Unknown.
Hyphal system: Monomitic, encrusted, subicular hyphae somewhat thick-walled, clamped, width (3.6) 3.9–5.1 (5.3) µm, x̄ = 4.5 µm (n = 10 hyphae).
Basidia: Repetitive basidia with four sterigmata, about 15 ✕ 5 µm.
Basidiospores: Narrowly cylindrical to allantoid, thin-walled, hyaline, inamyloid; length (6.4) 7.5–8.8 (9.4) µm, width (2.2) 2.5–2.9 (3.2) µm, x̄ = 8.2 ✕ 2.7, Q (2.1) 2.7–3.3 (3.5); biguttulate (two equally sized oil droplets situated at the poles of the spore), rarely one or three guttules, diameter (1.2) 1.3-1.6 (1.6) µm (n = 30 basidiospores).
Sterile Structures: Subulicystidia.
Notes: All measurements taken in KOH stained with phloxine. Basidia were difficult to observe.
UWMA0061, MO324084; 23 June 2018; University of Wisconsin Arboretum, Dane Co., WI, USA, 43.0563 -89.4055; leg. Alden Dirks, det. Alden Dirks, ref. Ordynets et al. (2018); Kriebel Fungarium PULF24589.
Gorjón, S. P., Greslebin, A. G., & Rajchenberg, M. (2011). Subulicystidium curvisporum sp. nov. (Hymenochaetales, Basidiomycota) from the Patagonian Andes. Mycotaxon, 118, 47–52.
Ordynets, A., Scherf, D., Pansegrau, F., Denecke, J., Lysenko, L., Larsson, K.-H., & Langer, E. (2018). Short-spored Subulicystidium (Trechisporales, Basidiomycota): High morphological diversity and only partly clear species boundaries. MycoKeys, 35, 41–99.