Pseudomarasmius R.H. Petersen & K.W. Hughes, gen. nov.

MycoBank number: MB 555729; Index Fungorum number: IF 555729; Facesoffungi number: FoF;

Differs from Marasmius by 1) diverticulate hyphae present in the pileipellis and 2) clamp connections absent.

Type species: Pseudomarasmius pallidocephalus (Gilliam) R.H. Petersen

Etymology: Referring to its similarity to Marasmius.

Basidiomata of three types: 1) similar in size and stature to those of Gymnopus sect. Androsacei, with discrete, bristle-like stipe and convex to applanate cap; rhizomorphs slender and inconspicuous limited to rotting leaf or needle litter; 2) similar in size and shape to those of Marasmiellus, with small, curved stipe and shell-like pileus and usually dominant rhizomorphs which occasionally produce basidiomata as side branches, similar to this phenomenon in Marasmius crinisequi; and 3) small, slender, pallid yellowish  mycenoid  basidiomata  lacking  rhizomorphs, on rotting needles of Abies or Picea. Microstructures resembling those of Gymnopus sect. Androsacei and Marasmius sect. Sicci, including:

  • diverticulate hyphae in pileipellis (arranged in a “rameales-structure”);
  • thick-walled, gelatinizing hyphae and/or gelatinizing diverticulate hyphae in pileipellis and subpellis; 3) without clamp connections or clamps rare and restricted to pileus trama;
  • basidia (2–)-4-spored;
  • spores similar to those of other gymnopoid genera, ellipsoid, thin- walled, inamyloid; 6) molecular (LSU, ITS) profiles unique, grouping into a monophyletic clade related to Rhodocollybia but more distant from groups exhibiting similar basidiomatal types (Fig. 15).

Key to species of Pseudomarasmius

  1. Ratio of pileus breadth to stipe length <2 (“thumb-tack shaped”);

basidiomata small, often arising as side branches of rhizomorphs        2

  1. Ratio of pileus breadth to stipe length >4; basidiomata marasmioid or mycenoid, arising as rhizomorph branch or independently on leaf litter or woody

substrate…………………………………………………………………….. 3

  1. Southern South America (Isla Chiloé, Chile); rhizomorphs inconspicuous, not producing basidiomata; fruiting on hardwood substrates;

clamp connections absent; superficially inseparable from

Ps. nidus-avis………………………………………………. Ps. patagonianus

  1. North American Gulf Coastal Plain and subtropical eastern Mexico; rhizomorphs dominant, long, occasionally branched, occasionally producing basidiomata as side branches; fruiting on small dead branches and twigs of deciduous trees usually at some distance from the ground; clamp connections occasional in

rhizomorphs and tramae but otherwise absent…… Ps. nidus-avis

  1. Antipodal (New Zealand); basidiomata minute (pileus 1–3.5 mm broad; stipe capillary, 6–8 mm long); fruiting on hanging dead terminal branches of Dacrydium;…………………………………………………… efibulatus
  2. Not Antipodal; fruiting substrate leaf or needle litter…………… 4
  3. Fruiting on conifer needle litter; rhizomorphs usually inconspicuous 5
  4. Fruiting on hardwood leaf litter (including Castanopsis); rhizomorphs conspicuous, resupinate on leaf surface……………………………………………… 7
  5. Temperate to northern North America; stipe black; basidiomata like those of Gymnopus Androsacei (pileus <35 mm broad; stipe 12–43 × 0.2–0.8 mm); pileus white to off-white; rhizomorphs inconspicuous, usually found deep in humus…………………………………………………….. Ps. pallidocephalus
  6. South Korea/eastern North America; basidiomata slender, mycenoid; stipe ochraceous to straw-colored;………………………………………… 6
  7. South Korea (and probably Japan); basidiomata minute, fragile

(pileus 48 mm broad; stipe 15–40 × 0.5 mm); pileus dark grey-green; stipe dark brown to black-brown; rhizomorphs inconspicuous;

fruiting on dead needles of Abies………………. Ps. glabrocystidiatus

  1. Eastern North America; basidiomata similar to those of glabrocystidiatus; pileus light brown or pale greyish brown; stipe brownish orange to yellow

or straw-colored; on rotting needles of Picea and Abies Ps. straminipes

  1. Costa Rica; high-altitude Quercus forests……………….. obscurus
  2. South Korea, China (Yunnan); on dead leaves of Castanopsis Ps. quercophiloides

Fig. 15. Maximum likelihood analysis of ribosomal RNA ITS sequences. Bootstrap values are given to the left of the supported node. Numbers are GenBank accession numbers (See Table 1). For collections from the United States and Canada, the state or province postal code is given. NZ = New Zealand.

Species