Trichia insularis Bortnikov, S.L. Stephenson, Prikhodko & Novozh., 2025

Bortnikov, F. M., Stephenson, S. L., Prikhodko, I. S. & Novozhilov, Yu. K., 2025, Another acidophilic corticolous species of Trichia (Myxomycetes) from Réunion Island, Phytotaxa 698 (1), pp. 43-50 : 45-48

Trichia insularis Bortnikov, S.L. Stephenson, Prikhodko & Novozh. sp. nov.

MycoBank: 856180. GenBank: nrSSU —PQ212585; EF1α—PQ216392; mtSSU—PQ212586.

Etymology:—from Latin īnsula—island, as the only known specimen was found on Réunion island.

Illustrations:— Fig. 2 , see also Adamonyte et al. 2011 (Fig. 3 A–D, as Hemitrichia sp. )

Description:—Sporocarps stalked sporangia, in small, densely packed groups, or rarely scattered, 750–940 μm high. Stalk tuberculous, somewhat furrowed, 34–48% total height (TH), dark greyish brown to dark brown, sometimes with a faint reddish tint, evenly coloured, filled with refuse matter. Sporotheca single, obovate to globose or somewhat depressed, 510–600 μm wide. Peridium two-layered. Inner layer thin, membranous, hyaline, decorated with numerous small straight striae, intersecting at different angles and forming a mosaic pattern. Outer layer consisting of grey-brown granular matter; external deposits sometimes practically monolithic, without any distinct peridium plates or with weakly defined peridium plates and blurry dehiscence lines. Dehiscence by preformed lines or almost irregular. Capillitium consisting of yellow or rusty yellow elaters, pale yellow in TL, apparently simple, but extremely long (observed fragments, broken from one or two sides, were 460–2500 μm long [mean = 969 μm]) and because of this have the appearance of a network (true branching is rare). Elaters (4.6–)5.1–6.2(–6.6) μm (n = 16) wide, with bulbous axillary and intercalary swellings up to 10(–15) μm wide and sometimes with spines up to 5(–10) μm long. Tips of elaters very short, ca. (4–)5–7 μm long, in the shape of a small thick spine on a bulbous thickening. Capillitial threads decorated with left-handed spiral bands, quite unevenly arranged, with ca. (7–)8–10 turns per 20 μm. By LM, spirals somewhat sharped and occasionally longitudinally split. Oil immersion reveals a barely noticeable secondary ornamentation in a form of longitudinal striae in between spirals. Under SEM, spirals rather high and blunt, sometimes slightly split. Secondary ornamentation of thin ridges, more or less parallel to the longitudinal axis of the elater; places where ridges from different spirals meet are also sometimes reticulate. Spores dark yellow in mass, pale yellow in TL, usually subglobose, but sometimes of somewhat irregular shape, sparsely warted (with 1.22–1.78 warts per μm 2), (9.4–)10.0–10.8(–11.2) μm diam. (mean = 10.38; SD = 0.41; n = 100). Under SEM, spore ornamentation pilate; pila distanced from one another. Secondary ornamentation absent. Plasmodium not observed.

Habitat:—dead bark of Cryptomeria japonica Lamb. , pH 4.3 (in moist chamber).

Distribution:—The species is known only from the type locality: Overseas France ( Réunion island).

Holotype:— FRANCE. Department of Réunion: Cilaos , botanic path, medium elevation semi-dry tropical forest, 21.1167 S, 55.4833 E, on dead bark of Cryptomeria japonica Lamb. , pH 4.3 (in moist chamber), bark collected May 15, 2006, specimen harvested in November 2006, leg. S.L. Stephenson, SLS21956, stored in LE, Saint-Petersburg, Russia ( LE F-352502).

Notes:— The new species unquestionably belongs to the species group Trichia acetocorticola Bortnikov — T. nubila Bortnikov — T. pinicola Bortnikov, Bortnikova & Novozh. , because it has the typical secondary ornamentation of the capillitium consisting of longitudinal striations and small reticulate areas (type 7 according to Bortnikov et al. 2023). However, the combination of its morphological traits is unique (see Table 1).

Trichia insularis is macroscopically similar to T. acetocorticola , as it has a grey-brown peridium without distinct brown or red shades, and the peridium plates are sometimes weakly expressed ( Fig. 2a ) and sometimes practically indistinguishable ( Fig. 2b ). In addition, sporocarps sometimes occur in dense groups, which is characteristic of T. acetocorticola var. aggregata Bortnikov & Bortnikova described from northern Vietnam from the bark of Pinus massoniana . However, T. acetocorticola has elaters with longer free tips (never less than 19 µm, on average more than 30 µm).

Trichia insularis microscopically is similar to T. nubila described from the Russian Far East. First, the diameter of spores in these two species is identical (mean values differ by 0.04 μm). Second, both species have extremely long elaters, which in the tangled state give the impression of a network (for this reason, the specimen we examined was previously identified and published as Hemitrichia sp. ). Third, the elater tips in these species are short. However, T. nubila still differs from the new species in several characters, including (1) the capillitium of T. insularis is slightly thinner, on average 5.1–6.2 μm vs. 6.1–6.8 μm in T. nubila and at the same time more irregular and often with swellings, which we did not find in T. nubila , (2) the free elater tips in T. insularis are quite short, almost reduced (4–)5–7 μm vs. 13–18 μm in T. nubila , (3) the peridium of T. insularis is not distinctly coloured with shades of red, as in T. nubila , and (4) the spores of Trichia insularis are ornamented with warts more sparsely scattered than those of T. nubila , on average 1.57 vs. 2.78 pcs/μm 2.

The ecology of the new species remains not fully resolved with only one collection known thus far. The specimen was obtained in a moist chamber on dead Cryptomeria japonica bark at pH 4.3. This brings it closer to T. acetocorticola and T. pinicola , which were found in moist chambers on bark of living trees at pH 4.0–5.2. However, the species closest in micromorphology to Trichia insularis is T. nubila (whose relatedness was confirmed by phylogenetic analysis [ Fig. 1 ]), which was found in the field on decaying wood. Consequently, it remains unclear whether T. insularis is an obligately corticolous species that was simply associated with the bark of a recently dead tree or whether this species is facultatively corticolous and may also be found on decaying wood. It should be noted that T. nubila is also known from a single collection thus far, and the ecological preferences of both species need to be clarified.

Figures

FIGURE 1. Phylogenetic tree for species of the order Trichiales as obtained with concatenated nrSSU and EF1α sequences. Branch supports are shown only for UBS ≥ 80 or PP ≥ 0.8; black dots indicate maximum supports in both analyses (UBS/PP = 100/1). Scale bar represent the mean number of nucleotide substitutions per site. The type species of the genera are shown in black bold. The type specimen of the new species is indicated in red bold.

FIGURE 2. Trichia insularis sp. nov. (holotype LE F-352502). a–c. Sporocarps. d. Spores. e. Elater tip. f. Capillitium and spores. g. Elater (SEM). h, i. Inner peridium under LM and SEM. j. Spore ornamentation (SEM). Scale bars: a–c = 500 µm (b, c—same scale), d, h = 10 µm, e–g, i = 5 µm, j = 1 µm.