Russula incrustata Buyck 2024, sp. nov.

Russula incrustata Buyck, sp. nov. (Figs 3; 5-8; 9D) Differs from R. koniamboensis Buyck, sp. nov., the only other member of Roseinae in New Caledonia, in the vividly coloured larger pileus with pale brown, orange, pink, lilac, purple or vinaceous colours, pinkish stipe, the somewhat smaller spore size and its occurrence under endemic Arillastrum gummiferum (Brongn. & Gris) Pancher ex Baill. (family Myrtaceae). TYPE MATERIAL. — New Caledonia • Les Bois du Sud, near blockhut; 22°17’17.13’’S, 166°76’01.03’’E; c. 300 m alt.; on ultramafic soil in monodominant rain forest of endemic Arillastrum gummiferum (family Myrtaceae); 27.III.2009; 735/BB09.172; holotype: PC0142414. ETYMOLOGY. — The epithet refers to the distinct incrustations present on the cell walls of the pseudoparenchyma in the lower pileipellis and other parts of the context. GENBANK. — OM370807 (ITS), KU237588 (LSU), KU237436 (mitSSU), KU237873 (rpb 2), KU238015 (tef 1), KU237728 (rpb 1). INDEX FUNGORUM. — IF 901190. DESCRIPTION Pileus Medium-sized, 64 mm diam., plane or very gently and widely depressed in the center, inconspicuously striate near margin; surface peeling ⅔ radius, dull, not hygrophanous, felty-velutinous, never viscid, not fragmenting in areolae or squamae but slightly concentrically pruinose, colour range from pale brown, orange, pink, lilac, purple or vinaceous, not paler in the center with age. Stipe 51× 11-12 mm, central, cylindrical; surface smooth, slightly longitudinally wrinkled, not pruinose, entirely pinkish but white at the extreme base, firm, context soft spongy without cavities, basal mycelium absent. 0.005 Lamellae Equal in length, adnate, without anastomoses or forks, brittle, 8 mm high, off-white. Context Brittle, white, colour unchanging on injury or with age, about 6 mm thick in pileus above gill attachment to stipe, with FeSO 4 hardly changing colour, merely faintly grey inside stipe and weakly pinkish on stipe surface, no reaction with Guaiac. Taste and odour not distinctive. Spore print White. Spores (6.46)6.89-7.27-7.65(7.92) × (5.42)5.67-5.92-6.17(6.46) µm, broadly ellipsoid, Q = (1.10)1.17-1.23-1.29(1.36); ornamentation subreticulate, composed of large, prominent, moderately distant, conical and strongly amyloid spines, up to 1.5 µm high, connected by frequent fine lines into an incomplete network; suprahilar spot well-developed, varying from strongly amyloid to verruculose, grayish and poorly amyloid. Basidia 30-40(-58) ×11-15 µm, narrowly to broadly clavate, 4-spored with stout sterigmata; basidiola clavate. Subhymenium Pseudoparenchymatic. Hymenial gloeocystidia On lamella sides mostly 50-74× 8-10 µm, clavate to fusiform, frequently mucronate to appendiculate at apex, up to 10 µm long, rarely obtuse rounded, originating in subhymenium and longer as basidia, walls up to 2(-2.5) µm thick; contents mainly restricted to some refringent inclusions at apex, not reacting to sulfovanillin, rarely with up to 5 secondary septa; cystidia near the lamellae edges smaller, up to 30 µm long. Marginal cells Occupying most of the lamellar edges, sitting on 1-2 basal cells, mostly 13-29 × (3-)5-9µ m, very variable in shape, several reminding of the terminal cells in the suprapellis (but smaller), but usually with 1-4 diverticulate pointed to obtuse-rounded outgrowths. Pileipellis Two-layered, not distinctly delimited from the underlying context; suprapellis composed in its lower part of a 60-80 µm thick, loose pseudoparenchyma of intertwined and strongly ramifying, ascending to erect, irregularly shaped cells, toward the loose subpellis carrying very distinct orthochromatic zebroid incrustations and with inflated basal cells up to 12(-15) µm wide; toward the pileus surface the pseudoparenchyma gives rise to short chains composed of 2-4(-5) smooth-walled, narrower cells; subterminal cells frequently branched, thin-walled, barrel-shaped or subcylindrical; terminal cells mostly longer in comparison and usually vertically oriented, (8-)16- 23(-39) × 2-4(6) µm, often undulated in outline, typically attenuating towards a minutely capitate apex or with one subapical lateral diverticulum. Primordial hyphae difficult to distinguish because of the poor contents, sometimes clearly recognizable because of their slightly wider and more voluminous terminal cell measuring 15-31 × 3-5 µm and filled with some refringent, granular-heteromorphous contents in their very upper part. Subpellis ill-defined, forming a loose structure c. 100 µm deep before the larger sphaerocytes of the context are present. Cystidioid hyphae absent from subpellis and context. Oleiferous hyphae or hyphal fragments abundant in subpellis and upper context. Clamp connections Absent. Notes Russula incrustata Buyck, sp. nov. is a beautiful and colourful species that we found only once. There are no environmental sequences available for it, which could indicate that this taxon is rather rare, particularly since there are quite some environmental sequences available for many other New Caledonian Russula in GenBank. Perhaps its ectomycorrhizal association with the rare and endemic Arrilastrum gummiferum (Myrtaceae) is the explanation. This potential rarity and the fact that there is no ongoing mycological inventory in New Caledonia, justifies in our opinon the decision to describe this species formally. In the multigene phylogenetic analysis of worldwide Russula (Buyck et al. 2018), this species was already clearly placed in Roseinae as “ R. roseinae sp. ined ” with additional sequences for ncLSU, mit SSU, rpb 2 and rpb 1 deposited in GenBank (as R. roseinae sp. VH-2016 strain 735/BB09.172).