Diploschistes infestans Kantvilas, 2025

Diploschistes infestans Kantvilas , sp. nov. ( Figs 1–2 View FIGURE 1 View FIGURE 2 )

MycoBank #MB 860367

Infecting the thalli of Stereocaulon species and distinguished from both D. muscorum (Scop.) R.Sant. and D. bartlettii (Lumbsch) Lücking by the smaller, urceolate apothecia to 0.8 mm wide, and the larger, ellipsoid, richly muriform ascospores, 26–46 × 12–22 µm, with 5–7(–8) transverse and 1–3 longitudinal septa.

Type: — AUSTRALIA. Tasmania, Mt Rufus, Gingerbread Track, 42°08’S 146°06’E, 1220 m, on the thallus of Stereocaulon on alpine sandstone outcrops, 18 March 2012, G. Kantvilas 254/12 ( holotype —HO 565067)

Thallus absent, entirely contained within the podetia of Stereocaulon and detectable only by the apothecia. Apothecia urceolate, commencing as a small hole or crack, expanding to 0.5–0.8 mm diam., immersed throughout development and at most causing a slight bulge or deformity in the host thallus; disc only slightly exposed at maturity, mostly obscured by the incurved margin, concave, dark grey to blackish; thalline margin unevenly to c. 60–110 µm thick when well developed, usually abraded in the upper part; proper exciple opaque dark brown, fused to the thalline margin in the lower part, in the upper part usually free and extending a little above the thalline exciple, dark grey and usually becoming radially split, abraded and whitish, in section 60–120 µm thick apically, 20–40 µm thick at the base; periphyses indistinct. Hypothecium 15–30 µm thick, hyaline to pale yellowish brown. Hymenium 110–160 µm thick, overlain by a brownish, granular epithecium; asci (2–)4–6(–8)-spored, (80–)120–140 × 20–30 µm. Ascospores ellipsoid, with rounded apices, never attenuated at the apices, 26– 33.4 –40(–46) × (12–)13.5– 16.9 –20(–22) µm ( n = 60), with 5–7(–8) transverse and 1–3 longitudinal septa; septa I+ purple; wall c. 0.5 µm thick. Pycnidia not seen.

Chemistry: —containing traces of lecanoric acid and diploschistesic acid, determined by LCMS; chemical extracts and spot tests are dominated and confounded by the chemical composition of the Stereocaulon host.

Etymology: —The specific epith et al ludes to the lichenicolous habit of the new species.

Remarks: —Hitherto only two species of Diploschistes , D. muscorum and D. bartlettii , are known to be lichenicolous. Both occur principally on the thallus of Cladonia , beginning their life cycles as parasites but eventually developing a widespreading thallus. The former is also recorded occurring on Stereocaulon ( Zhurbenko 2010) . The new species differs from these two taxa in that it does not appear to develop any thallus at all, and remains entirely within the thallus of its host where it can cause little more than gall-like swellings where the apothecia are formed, or it may cause the host podetia to become flattened to squamule-like. Furthermore, its apothecia generally remain deeply immersed and urceolate, whereas those of the other taxa become emergent, as much as 2 mm wide, and develop a widely exposed disc. More critically, the ascospores of the new species are considerably larger and more septate ( Fig. 2 View FIGURE 2 ). In D. muscorum , these are cited, for example by Aptroot et al. (2023b), as (20–)25–35(–40) × 12–15(–18) µm, with 5 transverse and 1–2 longitudinal septa, whereas in D. bartlettii , they are (17–)20– 24.8– 30(–31) × (8–)9– 10.4 –13 µm, with 3–5(–6) transverse and 0–1(–2) longitudinal septa (this study). Furthermore, whereas the ascospores in D. bartlettii and D. muscorum are frequently attenuated and tapered at the distal end, those of D. infestans are not, and are neatly ellipsoid to almost oblong, a shape difference also seen in the saxicolous species pair, D. gyrophoricus Lumbsch & Elix and D. sticticus (Körb.) Müll.Arg.

The single Tasmanian specimen seen was found on the thalli of Stereocaulon caespitosum Redinger and S. corticatulum Nyl. , two common and widespread species in alpine areas. Another specimen is known from New Zealand, parasitising S. ramulosum (Sw.) Räuschel , the most common Australasian species of this genus. Two further specimens are known from subantarctic Macquarie Island, also inhabiting S. ramulosum . In all specimens, the chemical composition of extracts is dominated by the chemistry of the host (atranorin and protocetraric acid in S. caespitosum ; atranorin and fatty acids in S. corticatulum ; and atranorin and perlatolic acid in S. ramulosum ).

Stereocaulon is known to be a favourable host for lichenicolous parasites, with 22 species recorded from the Holarctic by Zhurbenko (2010). It remains an uninvestigated habitat in Tasmania, although the discovery of and search for more material of Diploschistes infestans revealed at least one taxon of unknown affinities, as well as the first Southern Hemisphere record of Catillaria stereocaularum (Th.Fr.) H. Oliver [ AUSTRALIA: Tasmania, eastern slopes of Turrana Heights, 41°45’S 146°23’E, 1290 m, on thallus of Stereocaulon corticatulum , growing on dolerite pebbles, 1 January 2025, G. Kantvilas 33/25 (HO)].

Specimens examined: — NEW ZEALAND: Waipori Road, 2 November 1972, G.C. Bratt 72/1504 (HO). MACQUARIE ISLAND: Green Gorge, 54°30S 158°57’E, 50 m, 1980, R.D. Seppelt 11355, 11357 (HO).