Dictyonema gomezianum – Facesoffungi number: FoF 01050

Dictyonema gomezianum Lücking, Dal-Forno & Lawrey

Index Fungorum number: IF551502 Facesoffungi number: FoF01050

Etymology: Dedicated to the late Dr. Luis Diego Gómez, prominent Costa Rican botanist, naturalist, and conservationist and long-time director of Las Cruces Biological Station.

Holotype: R. Lücking 18053 (CR).

Diagnosis: Differing from the morphologically similar and related Dictyonema metallicum in the narrower cyanobacterial filaments with more or less paraplectenchymatous hyphal sheath and the very narrow associated hyphae. Thallus epiphytic on tree trunks and overgrowing nearby bryophytes, appressed filamentous, continuous, up to 5 cm across, forming a strongly compressed mat of horizontal, densely interwoven, dark aeruginous fibrils almost completely embedded in a gelatinous matrix with metallic shimmer, except for a broad, white, opaque, byssoid prothallus; thallus in section 50–100 μm thick, composed of an irregular photobiont layer and an irregular medulla or hypothallus. Photobiont Rhizonema, in a layer composed of numerous cyanobacterial filaments wrapped in a closed hyphal sheath formed by small, paraplectenchymatous or indistinctly jigsaw puzzle-shaped cells; cyanobacterial filaments composed of 7– 9 μm wide and 3–5 μm high, dark aeruginous cells penetrated by tubular fungal hyphae; heterocytes sparse, yellowish, 6– 10 μm wide and 2–4 μm high; cells of hyphal sheath angular to slightly wavy in lateral outline, 1.5–2 μm thick; hyphae associated with hyphal sheath straight, 2–3 μm thick, lacking clamp connections; compacted prothallus mostly formed by densely arranged empty hyphal sheaths admixed with straight hyphae. Hymenophore not observed. Secondary chemistry: no substances detected by TLC.

Material examined: COSTA RICA, Puntarenas, Las Cruces Biological Station near San Vito de Coto Brus; 82° 58′ W, 08° 47′ N, 1200 m; lower montane rain forest zone, on ridge beyond Río Java, on trunk of tree in disturbed primary forest; October 2004, R. Lücking 18053 (CR holotype; F isotype). Distribution and ecology: Known from lower montane rain forest in southern Costa Rica in the broader southern Central American Choco region.

Notes: Dictyonema gomezianum is similar and closely related to the recently described D. metallicum Lücking et al. (2013). Both share the strongly appressed, filamentous thallus in which the horizontally oriented fibrils are embedded in a gelatinous matrix that gives the thallus a strong metallic shimmer. While the phylogenetic distance between D. metallicum and its sister species, D. gomezianum, is considerable (DalForno et al., in prep.), the morphological differences are minor: D. metallicum has a thinner thallus with indistinct medulla, the cyanobacterial filaments are broader (likely influenced by the fungus which produces a sheath with more distinctly puzzle-shaped cells), and particularly the associated fungal hyphae are thicker (4–6 μm).