Dictyonema applanatum
Dictyonema applanatum is a little‑known, blue‑green basidiolichen in the family Hygrophoraceae. Formally described as a new species in 2013, it was discovered in the cloud forests of northern Bolivia. The species carpets bark and dangling vines with a thin, felt‑like layer of microscopic threads that weave together the fungus and its cyanobacterial partner.
Taxonomy
Dictyonema applanatum was introduced as a new species in 2013 by Robert Lücking, Manuela Dal Forno and Karina Wilk in a survey of Bolivian basidiolichens. The holotype was collected at elevation in Madidi National Park, La Paz Department, where it grew on a liana in lower montane rainforest. Morphologically the new taxon is set apart by a completely horizontal mat of cyanobacterial threads held down by a gelatinous, whitish film; this "flat" habit is echoed in the Latin epithet applanatum.Molecular data place the species in Dictyonema in the strict sense, one of five genera that make up the broader "Dictyonema clade" in the family Hygrophoraceae. Within that group D. applanatum belongs to the appressed‑filamentous grade, yet it is not closely related to the superficially similar D. metallicum from Ecuador.
Description
The lichen forms a tightly pressed, turquoise‑to‑aeruginous crust up to across. Under a hand lens it looks like a compressed felt made of countless, very fine threads lying parallel to the bark; a faint, shiny white peeks through in places.Each fibril is a chain of cyanobacterial cells wrapped in a sleeve of puzzle‑piece fungal cells. The entire layer is only 30–50 μm thick and lacks a separate medulla found in many lichens. Occasional heterocytes punctuate the cyanobacterial strand. The surrounding fungal hyphae are 4–6 μm wide, smooth, and lack clamp connections. No spore‑producing surface has been observed, so the species is presumed sterile in the available material.