Gymnopus portoricensis R.H. Petersen

Petersen, Ronald H. & Hughes, Karen W., 2019, Two additional species of Gymnopus (Euagarics, Basidiomycotina), MycoKeys 45, pp. 1-24 : 15-23

2. Gymnopus portoricensis R.H. Petersen sp. nov. Figs 10, 11, 12, 13, 14, 15

Holotype.

United States, Puerto Rico, Caribbean National Forest, El Yunque, vic. Sabana, trail 3, 1.VI.1992, coll RHP, TFB 4548 (TENN-F-051029). GenBank: KY026628-9.

Etymology.

Portoricensis referring to collections made in Puerto Rico.

Diagnosis.

1) Basidiomata small, resembling those of Gymnopus neobrevipes , arising from rhizomorphs or from woody substrate, often in clusters of significant numbers; 2) stipe slightly eccentric or central, strongly curved, dark brown (black only at base); 3) rhizomorphs luxuriant, brown (not black); 4) spores somewhat small for the clade, (5 –)6– 7 × (2.5 –)3– 4 µm.

Description.

Basidiomata (Fig. 10) marasmielloid, cespitose to imbricate, conchate when young becoming shallowly convex to applanate by maturity, stipitate. Pileus 2-11 mm broad, circular to broadly reniform, matt, radially rivulose outwards, thin, leathery, uniformly "light pinkish-cinnamon" (7A2) to “pinkish-cinnamon” (7B5). Lamellae well-defined (-0.6 mm broad and ventricose to reduced, pleated or fold-like, distant (total folds = 11-18; through folds = 7-10), concolorous to pileus or "tilleul buff" (7B2); edge entire. Stipe very small (1-2.5 × 0.5-0.7 mm), slender, central or eccentric, strongly curved to non-instititious attachment on substrate (wood or rhizomorph), "Mikado brown" (7C6) apically, downwards "warm sepia" (7F6), “bister” (5F8) to black; basal tuft insignificant, blond. Rhizomorphs extensive, slender, brown, near "tawny olive" (5C5) or "sayal brown" (6C5) to nearly black. Odour and taste negligible.

Habitat.

Outer surface of old bamboo (TENN-F-051029) or rotting twigs of deciduous trees (TENN-F-050999).

Pileipellis

(Figs 11A, B, 12, 13) composed of three elements involved in very thin mucoid matrix: 1) hair-like, probably erect hyphal apices (Figs 11B, 12), 30-120 × 1.5-3 µm (at widest point), subtly capitulate apically, arising as side branches of slender hyphae (not from clamps), firm- but indistinct-walled, delicately decorated with gritty deposits or a very thin mucoid sheath, tapering to 1-1.5 µm diam. and subrefringent especially at very apex; 2) repent, heavily ornamented hyphae (Figs 11A, 13B) 3-9 µm diam., firm-walled, strongly encrusted in stripes or patches with no profile calluses; contents more or less homogeneous; 3) scattered rudimentary diverticulate hyphal apices (Figs 11A, 13A) 4-7.5 μm diam., often appearing stout-tibiiform, with diverticula lobate, 2-5 × 1.5-2.5 µm; contents more or less homogeneous. Pileus trama loosely interwoven; hyphae (Fig. 13C) 3-7.5 μm diam., conspicuously clamped, appearing thick-walled but gelatinised (wall -1.5 μm thick). Pleurocystidia (Figs 11C, 14 A–D) 21-29 × 4-5 μm, fusiform, conspicuously clamped; contents homogeneous, occasionally subtly partitioned. Basidioles clavate, clamped; basidia (Figs 11C, 14F, G) 20-30 × 6-8 µm, 4-sterigmate, clavate, clamped; contents with scattered, minute guttules. Effete basidia do not disappear; at least the lateral walls survive to create debris in which turgid basidia are embedded in hymenial debris. Basidiospores (Fig. 11D) (5 –)6– 7 × (2.5 –)3– 4 µm (Q = 1.50-2.83; Qm = 2.08; Lm = 6.58 µm), narrowly pip-shaped to sublacrymiform (somewhat tapered towards apiculus), thin-walled, smooth, inamyloid; contents homogeneous. Cheilocystidia (Fig. 15) limited to well-defined lamellae, scattered, 25-35 × 7-15 µm, pedicellate, thin-walled (easily crushed), expanded distally usually with irregular lobes or apical outgrowths, obscurely clamped, hyaline; contents more or less homogeneous. Stipe medullary hyphae of three types: 1) 6.5-24 μm diam., thick-walled, irregularly gelatinising [wall -1.2 μm thick in H2O, wall up to 7 μm thick in KOH and then yellowish (PhC)]; 2) 5-7.5 μm diam., thick-walled (wall -1 μm thick, not gelatinising, hyaline); clamp connections occasional, obscure; and 3) 2-4 μm diam., firm-walled, meandering through medulla; clamp connections rare, conspicuous. Stipe cortical hyphae 4-8 μm diam., strictly parallel, apparently adherent (held together adhesively and shattering under pressure), thick-walled [wall -2 μm thick, pigmented (ochraceous tan in KOH, red-brown in IKI/BF)], coarsely roughened in pigmented spicules; clamp connections not observed.

Commentary.

Although basidiomata superficially resemble those of G. neobrevipes , the pileipellis structure is not similar. Erect, broom cell-like cells of G. neobrevipes are missing; diverticulate repent hyphae are rare and doubtful; erect “hairs,” while clamped (and therefore assumed to belong to this organism), are more demonstrable in G. neobrevipes . Morphologically, G. portoricensis could be placed in Marasmiellus (see Retnowati 2018) based on poorly developed Ramealis-structure, no broom cells), but it equally could be interpreted as a reduced member of Androsacei (including G. neobrevipes ) in which erect, broom cell-like pileipellis cells are rare to missing. Cheilocystidia are typical of the latter group. If G. neobrevipes is accommodated in Gymnopus sect. Androsacei , G. portoricensis must also be found there. ITS sequences confirm this placement (Fig. 2).

Inspection shows that almost no basidiomata originate from rhizomorphs, instead seemingly originating from woody substrate directly. Rare basidiomata, however, do arise from rhizomorphs, with stipes as side branches. Moreover, some twigs with basidiomata are devoid of rhizomorphs altogether.

A polyspore dikaryon culture was established from TENN-F-050999 and careful examination revealed exceedingly rare (but clearly demonstrated) clamp connections. This condition is also true in cultures of G. neobrevipes . Desjardin (1990), while reporting clamp connections in the culture of M. brevipes , made no comment on their relative abundance.

Basidiomata are not pseudo- or eccentrically stipitate, but centrally to slightly eccentrically stipitate. The stipe, however, is usually immediately curved through the declivity in the pileus circumference. Lamellae appear to deteriorate rapidly, perhaps through insect grazing or tissue gelatinisation, but when discrete are shallow but sharp ly defined (not merely as folds). Interlamellar anastomoses are absent and even lamellar buttressing is missing. Instead, the interlamellar hymenophore is smooth.

These two collections fruited on very different substrata. The origin within bamboo structures would be difficult to imagine, so perhaps basidiomata arise from a very thin, arachnoid mycelium on the bamboo surface. Rare basidiomata were seen attached to rhizomorphs, which might support typical attachment to somatic hyphae.

If G. portoricensis is regarded as in Marasmius , the epithet (portoricensis) is preoccupied by Marasmius portoricensis Murrill in Pennington. 1915. North American Flora 9(4): 262. The homonym is in Marasmius but not in Gymnopus . Described as having the longest ("longissimus") stipe - 6-8 cm × 0.5 mm - and pileus 4-10 mm broad, the holotype of Marasmius portoricensis is at NY (isotype MICH) and the Mycoportal record shows several long-stiped basidiomata with stipe yellow-orange and apparently several long, straight rhizomorphs of similar colour.

An ITS-based clade (Fig. 2), which includes Gymnopus neobrevipes , G. portoricensis , two environmental sequences from Okinawa and a sequence of Gymnopus cremeostipitatus from Korea, is sister to the rest of Gymnopus sect. Androsacesi . This section continues to expand with additional taxa yet to be determined and described.

Auxiliary specimen examined.

United States, Puerto Rico, Caribbean National Forest, El Junque, road to Verada Bisley, 18°15'53"N, 65°45'13"W V.1992, coll RHP, TFB 4512 (TENN-F-050999).