Russula koniamboensis Buyck 2024, sp. nov.

Russula koniamboensis Buyck, sp. nov.

(Figs 4; 9 A-C; 10-14)

Differs from R. incrustata Buyck, sp. nov. in the pale yellowish pileus, white stipe, the somewhat larger spore size and its occurrence under Nothofagus Blume; from R. purpureotincta again in the white yellowish pileus (which is pink, vinaceous and purple in R. purpureotincta) and its occurrence in New Caledonia, not New Zealand.

TYPE MATERIAL. — New Caledonia • Northern Prov., Massif du Koniambo, near Voh, in the nickel mine exploitation site called ‘ Niko’; 21°00’22’’S, 164°49’51’’E; 724 m alt.; on ultramafic soil under Nothofagus balansae; 17.III.2009; leg. B. Buyck; 722/ BB09.022; holotype: PC0142407.

ETYMOLOGY. — Named after the type locality.

GENBANK. — OM397457, OM397457 (ITS), OM365994- OM365996 (tef 1).

INDEX FUNGORUM. — FI 90189

ADDITIONAL EXAMINED MATERIAL. — New Caledonia • Northern Prov., Massif du Koniambo, near Voh, in the “île nickel” mine exploitation site; 21°00’42”S, 164°49’50”E; 734 m alt.; on ultramafic soil under Nothofagus balansae; 19.III.2009; leg. B. Buyck; 730/ BB09.117; PC0714855 • Massif du Koniambo, near the Trazy entry of the nickel mine exploitation site; on ultramafic soil under Nothofagus codonandra; 9.IV.2009; leg. B. Buyck; 742/ BB09.346; PC0714856.

PILEUS

25-30 mm diam., convex, slightly depressed in the center, near the margin striate over ⅓-¼ of the radius, surface dull, smooth to finely or even distinctly farinaceous in the center and more or less concentrically deposited, peeling ⅔ of the radius, pale yellowish in the center, cream towards margin.

LAMELLAE

Equal in length, adnate, distant and c. 1-2 L/mm at pileus margin, off-white to cream colour, obtusely rounded at the pileus margin; entire edge concolourous.

Stipe

30-34× 6-8 mm, central, cylindrical to slightly obclavate, glabrous, smooth to finely longitudinally striate, white to ivory, pale greyish towards base, brittle, spongy inside, lacunes absent.

Context

Very thin toward the margin, white, distinctly greying in age. Taste and odor not distinctive.

Spore print

White.

Spores

(6.67)7.51-8.01-8.51 (8.75) × (6.25)6.52-6.83- 7.15(7.29) µm, Q = (1.06)1.10-1.17-1.24(1.31), subglobose to broadly ellipsoid; ornamentation subreticulate, composed of large, prominent, moderately distant, conical to hemispherical and strongly amyloid spines, up to 1(-1.5) µm long, connected by dispersed to frequent fine lines into a (very) incomplete network; suprahilar spot well-developed, varying from strongly amyloid to verruculose and grayish to poorly amyloid.

Basidia

30-42 × 12-17 µm, fusiformous to distinctly clavate, with (2-)4 stout sterigmata; basidiola clavate.

Subhymenium

Pseudoparenchymatic.

Hymenial gloeocystidia

68-94 × 7-12 µm on lamella sides, smaller near the lamella edges, up to 45 µm long, narrowly clavate to fusiform or subcylindrical, frequently mucronate to appendiculate at the apex, up to 14 µm long, originating in subhymenium and protruding beyond the basidia, thin-walled with walls up to 1 µm thick; contents in Congo red mainly restricted to dispersed refringent inclusions of variable size that do not react to sulfovanillin.

Marginal cells

15-26(-34)× 4-6(-9) µm, sitting on 1-2 short, subterminal cells, small, occupying most of the lamellar edges, extremely variable in shape, similar to the smaller terminal cells in the suprapellis in having 1-4 diverticulate, obtuse lobes or outgrowths.

Pileipellis

Two-layered; suprapellis composed in its lower part of hyphae with or without distinct orthochromatic incrustations, forming a 40-50 µm deep pseudoparenchyma of intertwined and strongly ramifying, irregularly shaped, thin-walled cells; basal cells sometimes up to 20(-25) µm wide; near the surface this suprapellis gradually transits into short chains composed of 2-4(-5) narrower cells that are slightly inflated and barrel-shaped or ellipsoid to subcylindrical, up to 10 µm wide; terminal cells of variable size are more or less arranged in a trichodermal structure, either longer or shorter than subterminal cells, (8-)16-23(-34)× 2-4(-6) µm, often very irregular or undulate in outline, slightly attenuating toward the frequently capitate, appendiculate or diverticulate apex. Primordial hyphae recognizable mostly by their somewhat more regular (i.e., cylindrical) outline, but especially by the refringent granular-heteromorphic contents of the terminal cell that mostly measures 15-25 × 4-5 µm, narrowly clavate to subcylindrical in outline, obtuse-rounded at the apex, diverticula or appendages absent, thin-walled; subpellis 60-70 µm deep, forming a loose structure above the first large sphaerocytes of the underlying context. Cystidioid hyphae absent in subpellis and context. Oleiferous hyphae rare in subpellis.

Clamp connections

Absent.

NOTES

The above description is based on the holotype collection. However, the two other collections of this species (having identical ITS sequences) clearly show that its microscopic features are quite variable among different collections (Fig. 14). For the pileipellis this variation concerns the size of the sphaerocytes in the lower suprapellis which are sometimes up to 35 µm diam., giving rise to 8-celled chains (as in BB 09.346); observed variations apply also to the distinctiveness of the orthochromatic zebroid incrustations on the cell walls in the lower supra- and subpellis (as in BB 09.117) and finally also to the form of the terminal cells on the hyphae, which can be either more regular in outline and thus similar to those of R. incrustata Buyck, sp. nov. (as in BB 09.346 and BB 09.117) or they can be strongly diverticulate as in the type collection. On the lamella edge, cheilocystidia can be abundant and well-developed (as in BB 09.346) or just widely dispersed among the other elements. The spores in BB 09.346 are near-identical in size and ornamentation to the holotype [(8.13)8.20-8.63- 9.05(9.38)×(6.25)6.47-6.86-7.26(7.50)µ m, Q =(1.11)1.17- 1.26-1.35(1.40)], while spores in BB 09.117 produced several aberrant sizes and ornamentations indicating an unfavourable development. These spores were, therefore, not used for measurements.