Dictyonema subinvolutum V. Marcano, 2022

Marcano, Vicente, 2022, Eight new species of lichenized Basidiomycota in the genera Acantholichen, Cyphellostereum and Dictyonema s. str. (Agaricales, Hygrophoraceae) from northern South America, Phytotaxa 574 (3), pp. 199-225 : 215

6) Dictyonema subinvolutum V. Marcano , sp. nov.; ( Fig. 9 )

Mycobank MB#838447

Diagnosis:— Sicut Dictyonema obscuratum , sed hyphis fibulatis differt. Thallus muscicola vel terricola, crassiusculus. Prothallus nullus. Hyphis tegentibus fibrillas quadrato-rhombicis. Haustoria praesentia. Filamenta 12–15 μm lata. Hymenocarpus resupinatus, pruinosus, margine subinvoluto. Hymenium N reagens (roseus). Sporis guttiformis, hyalinis, non septatis, 6–7 μm longis, 4–5 μm latis.

Type:— VENEZUELA. Mérida: Parque Sierra Nevada de Mérida, Raiz de Agua cloud forests, elev. 2650 m; 5 June 2020, V. Marcano & L. Castillo 20-411 (holotype MER, isotype B, private herb. V. Marcano) .

Etymology:—The epithet refers to the slightly involute hymenophore margins.

Description:— Thallus growing on soil and among bryophytes, filamentous, dark blue-green, moderately thick, developing a mat of interwoven fungal-cyanobacterial fibrils, leaving interspaces connected by a defined hypothallus; prothallus absent. Fibrils markedly ascendent, with yellow or pale brown apices, forming an irregular, rough surface. Thallus (when fresh) in section 1.75–2.3 mm thick, composed of a thick, loose, photobiont ( Rhizonema ) layer (1–1.3 mm) and a thick, pale brown medulla (0.75–1 mm) (hypothallus); photobiont layer composed of numerous cyanobacterial filaments wrapped in a closed hyphal sheath formed by jigsaw-puzzle-shaped cells; cyanobacterial filaments occasionally branched, composed of 12–15(–17) μm wide and 5–7 μm high, bluish green cells penetrated by tubular fungal hyphae (haustoria); heterocytes frequent, pale to slightly bright yellow, 8.5–11 μm wide and 2–5.5 μm high; cells of hyphal sheath variably wavy in lateral outline, 4–5 μm thick; hyphae of hypothallus straight, branched, hyaline, smooth, 7–8 μm thick. Clamp connections present.

Hymenophore (when fresh) developed as effuse patches, 3–7 mm diameter, white, resupinate, with slightly involute margins and a smooth, pruinose surface; hymenophore in section 120–130 μm thick, composed of a paraplectenchymatous layer connected to loose medullary hyphae, 5–6 μm wide; hymenium composed of numerous, palisade-like basidioles and scattered basidia; basidiospores drop-shaped, non-septate, hyaline, 6–7 × 4–5 μm.

Chemistry:—Thallus K–, C–, KC–, P–; medulla K–, C–, KC–, P–, N+ (pink), ER+ (pale bluish purple); basidiocarp K–, C–, KC–, P–, N+ (pink), ER+ (pale bluish purple) (n = 6). No lichen compounds detected by TLC.

Distribution and Ecology:— Dictyonema subinvolutum was found growing on mosses and acid soils in shady and very humid rainforest at elev. 2250 m ( Fig. 7A ). This species is only known from the well-developed type collection.

Remarks:— Dictyonema subinvolutum is readily distinguished by its moderately thick thallus, markedly ascendent fibrils, a thick hypothallus, the presence of clamp connections, resupinate, pruinose, N+ pink basidiocarps, and the lack of a prothallus. The medulla turning pink by the N spot test appears to be a diagnostic feature due to its occurrence only in this taxon among the Dictyonema specimens examined. Dictyonema subinvolutum is like D. obscuratum . Both species are characterized by numerous cyanobacterial filaments covered by fungal hyphae, forming jigsaw-puzzleshaped cells. However, D. obscuratum has strongly compressed mats of irregular, densely interwoven, very dark olivegreen fibrils, an indistinct hypothallus, absence of clamp connections and the hyphae are often sparsely and finely papillose towards the tips. Furthermore, D. obscuratum has slightly longer spores (7–9 μm) than D. subinvolutum . In addition, D. obscuratum inhabits the Cerrado vegetation of Brazil, where it is found growing on tree trunks ( Lücking et al. 2013b) (Table 1). Dictyonema subinvolutum could also be confused with D. schenckianum ( Müller Argoviensis 1891: 234) Zahlbruckner (1931: 748) . However, the type material of D. schenckianum lacks clamp connections and presents a combed appearance ( Lücking et al. 2013a). This species is known from Brazil and Colombia ( Dal Forno 2015).

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. 20-562 (MER, private herb. V. Marcano).

Figures

FIGURE 7. Dictyonema duidense. A. Habit of the species growing on bark. Photos by V. Marcano.

FIGURE 9. Dictyonema subinvolutum. A. Habit of the species, scale = 1 cm. B. Mature thallus with basidiocarp, scale = 0.5 cm. C. Close up showing hymenophore, scale = 0.3 cm. Photos by V. Marcano.