Dictyonema subsericeum 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 : 216-218

7) Dictyonema subsericeum V. Marcano , sp. nov.; ( Fig. 10 )

MycoBank MB#838497

Diagnosis:— Sicut Dictyonema sericeum , sed sed hyphis fibulatis differt. Thallus corticola, byssaceus, crassus, pagina hirsuta. Lobis spongiosis, maxime variantibus statura magnitudine latitudine colore et forma. Hymenocarpus resupinatus, hapteriformi. Hymenium N non reagens. Sporis guttaeformibus, hyalinis, non septatis, 4.5–5.5 μm longis, 3.7–4.7μm latis.

Type:— VENEZUELA. Mérida: Parque Sierra Nevada de Mérida, Raiz de Agua cloud forests, elev. 2650 m; 5 June 2020, V. Marcano & L. Castillo 20-84 (holotype MER, isotype B, private herb. V. Marcano) .

Etymology:—The epithet refers to the thallus appearing closely related to the species D. sericeum .

Description:— Thallus corticolous, byssaceous, filamentous, forming a thick crust, epiphytic on tree branches. Thallus surface plane or irregular, projecting horizontally from the substrate, covering up to 20 cm diameter, composed of numerous imbricate to partially fused lobes. Lobes projecting parallel from the substrate, semicircular or hemispherical, variable in color, size and shape, when small forming white, filamentous finger-like outgrowths, 4–7 mm broad, when large semicircular, 18–21 mm broad, greenish blue in the bottom side with fibrillose, white margins, 4–5.5 mm broad, and when located in the center of the thallus, brown, forming hemispherical clusters, 5–7(–8) mm broad; surface hirsute. Thallus (when fresh) in section 3–5.8 mm thick, composed of an appressed, pale brown medulla (1.6–2.5 mm) (hypothallus), a broad, very loose, aeruginous photobiont ( Rhizonema ) layer (1–3 mm) and frequently with an upper layer (0.5–1.25 mm) composed of irregularly arranged, long, white fibrils, lacking photobiont filaments; photobiont layer composed of numerous cyanobacterial filaments wrapped in a closed hyphal sheath formed by jigsawpuzzle-shaped cells; cyanobacterial filaments not divided, composed of 22–27 μm wide and 4.5–7(–8) μm high, bluish green cells penetrated by tubular fungal hyphae (haustoria); heterocytes frequent, bright yellow, elliptic, 13–18 μm wide and 5–8 μm high; hyphae associated with hyphal sheath straight, hyaline, 5–6 μm thick, with clamp connections, finely papillose just before the apices.

Hymenophore (when fresh) developed as small, angular to elongate, white, resupinate patches dispersed on the underside and resembling irregular, large (500–1200 μm wide) attachment hapters with white, more or less smooth or pruinose surface, and fibrillose margins; hymenophore composed of a paraplectenchymatous layer connected to loose medullary hyphae, 6–7.5 μm wide; hymenium composed of numerous, palisade-like basidioles and scattered basidia; basidia 28–37 × 4–6 μm, 4-sterigmate; basidiospores globose or subglobose, non-septate, hyaline, 4.5–5.5 × 3.7–4.7 μm.

Chemistry:—Thallus K–, C–, KC–, P–; medulla K–, C–, KC–, P–, N–, ER–; basidiocarp K–, C–, KC–, P–, N–, ER– (n = 8). No lichen compounds detected by TLC.

Distribution and Ecology:— Dictyonema subsericeum was found growing as an epiphyte on branches in the canopy of rainforests at elev. 2200–2250 m ( Fig. 8A ). It is known only from the well-developed type collection.

Remarks:—Molecular phylogenetic data clearly show that D. sericeum sensu Parmasto contains many different species and even the shelf-like forms representing D. sericeum in a narrow sense are more than one species ( Dal Forno et al. 2013). Dictyonema subsericeum is characterized by a thallus forming a thick crust, filamentous lobes, variability of color (white, greenish blue, brown), size and shape (semicircular and hemispherical), with a hirsute surface, fibrillose margins, clamp connections on the hyphae, a hymenophore resembling large, irregular attachment hapters with a white surface and a negative N spot test. Dictyonema subsericeum is like D. sericeum ( Dal Forno et al. 2013) , D. hapteriferum and D. spongiosum Berkeley & M. A. Curtis (1868: 335) , the latter representing the lineage labeled D. sericeum 3 in Dal Forno et al. (2013). These species are characterized by semicircular, shelf-like, filamentous lobes and absence of clamp connections. Dictyonema hapteriferum has aeruginous fibrils bordered by a narrow, byssoid, white margin, a hymenophore resembling attachment hapters with beige, smooth surface. Dictyonema spongiosum has a thick, spongiose upper surface composed of bundles of vertically projecting fibrils and it is known only from Cuba and Guatemala.

Dictyonema subsericeum might also be confused with D. irpicinum and D. ligulatum ( Krempelhuber 1875: 15) Zahlbruckner (1908: 239) . Both species have a lobed surface mottled white and blue-green with coarse, finger-like outgrowths, and hyphae with clamp connections but they are restricted to the Paleotropics ( Lücking et al. 2013a, Dal Forno 2015, Dal Forno et al. 2019). Dictyonema subsericeum is like to D. album Lücking & Timdal (2016: 192) from Mauritius. However, this latter species has a combination of irregularly arranged tufts of fibrils that do not form a distinctly layered thallus, being dominated by straight hyphae with very few associated cyanobacterial fibrils, giving the thallus a whitish appearance and it lacks clamp connections on the hyphae ( Lücking & Timdal 2016).

Additional specimens examined (paratypes):— Mérida: Parque Sierra Nevada de Mérida, Raiz de Agua, cloud forests, elev. 2650 m; V. Marcano & L. Castillo no. 20-85 (MER, private herb. V. Marcano).

Figures

FIGURE 8. Dictyonema laurae. A. Habit of the species growing on bryophytes, scale = 2.5 cm. B. Thalli showing irregular, ascendant to erect fibrils, scale = 1 cm. C. Close up showing hymenophore developed on the underside, scale = 0.4 cm. D. Details on aeruginous fibrils of the thallus upper layer, scale = 0.2 cm. Photos by V. Marcano.

FIGURE 10. Dictyonema subsericeum. A. Habit of the species growing on bark, scale = 5 cm. B. Mature thallus with basidiocarp, scale = 0.5 cm. C. Close up showing hymenophore, scale = 0.4 cm. Photos by V. Marcano.