Multiclavula ichthyiformis

The thallus of M. ichthyiformis forms a thin, greenish film—rarely more than 5 cm (2 in) across—composed of densely packed cells of the unicellular green algal genus Coccomyxa. Each alga is ensheathed by a single hyphal layer, creating microscopic bulbils that also appear on the stipe and lamina. Photobiont cells are broadly ellipsoid (7–9 × 4–7 μm) and frequently divide by autospory. Fungal hyphae within the thallus are hyaline, thin-walled, and sparsely branched.^[2]

Basidiocarps occur singly on the soil surface. The stipe, 2–5 mm tall and up to 0.7 mm thick, is flesh-coloured when moist and turns translucent white on drying; its surface is lined with pointed scales 0.1–0.4 mm long that incorporate algal cells. Above the stipe the lamina abruptly widens to 0.9–1.9 mm, forming a flat, dorsiventral blade 0.6–4 mm high. The sterile upper face carries a thin gelatinised cortex overlain by orange-brown crystalline aggregates, which impart an ochraceous hue in the dry state, whereas the lower face bears the hymenium. Basidia (spore-bearing cells) are somewhat urn-shaped (urniform) (25–35 × 7–10 μm) and usually six-spored; basidiospores are smooth, thin-walled, spherical, and hyaline. Hyphae in the context are tightly parallel and agglutinated, measuring 3–4 μm wide in the lamina and 1.5–2 μm in the scales and outer stipe.^[2]

Multiclavula ichthyiformis is known only from its type locality, a disturbed peat bog in upper montane rainforest just below the páramo zone on the Pacific slope of the Cordillera de Talamanca. It grows on persistently moist, acid soil along a small brook and on a roadside bank, typically among bryophyte cushions. Associated ground-dwelling lichens include Cladia aggregata, Cladonia confusa, Dictyonema glabratum, Icmadophila aversa, Phyllobaeis imbricata, and Siphula ceratites. The habitat—a remnant of high-elevation bogs scattered along the Inter-American crest—is considered ecologically sensitive owing to ongoing land-use pressures and climatic change.^[2]