Dictyonema andinum V. Marcano 2022, sp. nov.
Creators: name: Marcano, Vicente
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Fungi
Basidiomycota
Agaricomycetes
Agaricales
Hygrophoraceae
Dictyonema
Dictyonema andinum

description: 3) Dictyonema andinum V. Marcano, sp. nov.; (Fig. 6)
Mycobank MB#838341
Diagnosis:— Sicut Dictyonema irrigatum, sed fibrilis ascendentibus vel verticalibus differt. Thallus muscicola vel terricola, crassiusculus. Hyphis tegentibus fibrillas quadrato-rhombicis, undulatis, fibulatis. Haustoria praesentia. Filamenta 20–25 μm lata. Hymenocarpus corticoideus. Hymenium N reagens (rubescens), sporis guttaeformibus, hyalinis, non septatis, 5–6 μm longis.
Type:— VENEZUELA. Mérida: Parque Sierra Nevada de Mérida, Raiz de Agua, cloud forests, elev. 2650 m; 12 October 2020, V. Marcano & L. Castillo no. 20-535 (holotype MER, isotype B, private herb. V. Marcano).
Etymology:—The epithet refers to the geographical region where the type specimens were collected.
Description:— Thallus filamentous, dark blue-green, covering larger areas of the substrate, in irregular, confluent patches up to 45 cm across, forming a crust usually over bryophytes or soil, composed of loosely interwoven, dark green to bluish green fibrils leaving interspaces and bordered by a discrete, white margin (prothallus). Fibrils irregularly arranged, ascending or erect, forming an irregular, lumpy surface. Thallus furnished with irregular, small tufts, projecting vertically from the substrate, consisting of pale brown or green fibrils. Thallus (when fresh) in section 2–2.4 mm thick, composed of a thick photobiont (Rhizonema) layer (1.25–1.75 mm) and a thin, pale brown medulla (375–500 μm) (hypothallus); photobiont layer composed of numerous cyanobacterial filaments wrapped in a closed hyphal sheath formed by jigsaw-puzzle-shaped cells; cyanobacterial filaments not branched, composed of 20–25 μm wide and 7–8(–10) μm high, bluish green cells penetrated by tubular fungal hyphae (haustoria); heterocytes frequent, pale to slightly bright yellow, 10–12(–14) μm wide and 3–4(–5) μm high; cells of hyphal sheath variably wavy in lateral outline, 4–6 μm thick; hyphae of medulla, hypothallus and white margin (prothallus) straight, hyaline, much branched, 5–7 μm thick. Clamp connections present but sparse on the hyphae; hyphal sheath finely papillose towards the tips of the filaments; hypothallus and prothallus formed by interwoven, strongly agglutinate, generative hyphae; often fertile.
Hymenophore (when fresh) developed as bulging, stereoid-corticioid patches from the underside of the thallus margins and soon becoming inverted and exposed, white patches, 6–14 mm wide; smooth, with pruinose upper surface and spongy lower surface; hymenophore in section 150–350 μm thick, composed of a paraplectenchymatous layer connected to loose medullary hyphae; hymenium composed of numerous, palisade-like basidioles and scattered basidia; basidioles 25–35 × 5–6 μm; basidia 30–40 × 5–7 μm, 4–sterigmate; basidiospores ellipsoid to narrowly drop-shaped, non-septate, hyaline, 5–6(–7) × 3.8–4(–5) μm.
Chemistry:—Thallus K–, C–, KC–, P–; medulla K–, C–, KC–, P–, N+ (dark red), ER+ (purple); basidiocarp K–, C–, KC–, P–, N+ (red), ER+ (bluish purple) (n = 8). No lichen compounds detected by TLC.
Distribution and Ecology:— D. andinum is the most abundant of all the species of Dictyonema s.str. found in the Venezuelan Andes. Six populations were observed in an area ca. 2 km 2. It was found growing on mosses and acid soils, associated with Dibaeis absoluta and Cladonia ceratophylla (Swartz 1788: 147) Sprengel (1827: 271) in partly exposed and very humid rainforest at 2000–2450 m (Fig. 5A).
Remarks:—Morphologically, D. andinum is a typical representative of Dictyonema s.str. This species is characterized by irregularly arranged, broad, ascending, or erect fibrils, thick photobiont layer and hypothallus, finely papillose hyphae towards the tips of the filaments, clamp connections, and a white, stereoid-corticioid hymenophore. Commonly the thallus is slightly thicker when the specimen is fresh (humid). Positive (red) N spot test in the hymenophore and medulla are notable and suggest the presence of certain compounds which are absent in other Dictyonema species.
Dictyonema andinum could be confused with D. irrigatum (Berkeley & M.A. Curtis 1860: 123) Lücking (2013b: 30). However, D. irrigatum has irregularly appressed, horizontal to erect fibrils, and a hymenophore developed as resupinate patches. Its spores are also slightly longer (7–9 μm) than those of D. andinum. Dictyonema irrigatum is known only from China and the Andaman and Nicobar Islands (Lücking et al. 2013 a, Jagadesh-Ram & Singh 2014) (Table 1).
Additional specimens examined (paratypes):— Mérida: Parque Sierra Nevada de Mérida, Raiz de Agua, cloud forests, elev. 2650 m; 12 October 2020, V. Marcano & L. Castillo no. 20-540 (MER, private herb. V. Marcano); Parque Sierra Nevada de Mérida, road towards Lake Coromoto, cloud forest, elev. 2000 m, V. Marcano & L. Castillo 21-119, 21-120 (MER, private herb. V. Marcano).
description: Published as part of Marcano, Vicente, 2022, Eight new species of lichenized Basidiomycota in the genera Acantholichen, Cyphellostereum and Dictyonema s. str. (Agaricales, Hygrophoraceae) from northern South America, pp. 199-225 in Phytotaxa 574 (3) on pages 210-211, DOI: 10.11646/phytotaxa.574.3.1, http://zenodo.org/record/7380966