VICTORIA. Alexandra, near Wildflower Res., subhypogeal in a Pinus radiata plantation, 10 Aug. 1974, G. Crichton & G. Beaton 63; Warburton, Big River Camp pine plantation, hypogeal at base of eucalyptus stump, 29 May 1974, D. Wallis in Beaton 71.

Gasterocarp 1 5-3(-6) cm diam., subglobose to irregularly ellipsoid, attached on the lower half by scanty, yellowish rhizomorphs which blacken on drying. Peridium at first cream colour to light yellowish brown, drying reddish brown to almost black, with some reddish purple patches, smooth to finely wrinkled or irregularly tessellate. Gleba at first cream colour then Pompeian yellow (M.8.5YR/6.2/6.2), darkening from the centre to olive-brown at maturity, labyrinthoid, composed of partially filled, irregular chambers, 0 2-1 mm diam. Tramal plates 100-175 µm thick, subgelatinous to gelatinous, consisting of a narrow hymenophoral trama and moderately developed subhymenial layers; peridial context neither gelatinized nor agglutinated, with thin-walled, uninflated or slightly inflated hyphae, 2 5-14 µm diam., together with scattered oleaginous hyphae, 8-12 µm diam., with hyaline, refractive contents; clamp-connexions absent. Spores 7.5-10.5 x 2.5- 4(9± 0.5 x 3.5± 0.2) µm, Q= 2.57, symmetric or nearly so, cylindrico-ellipsoid, with a small basal scar but scarcely truncate, at first hyaline becoming pale brown, with a slightly thickened smooth wall. Basidia 22-28 x 7-8 µm, lageniform with a ventricose base and a tapering apex, developing a variable number of sterigmata, but mostly four or six; numerous immature, ovoid basidia also present. Basidioles few to abundant, sometimes dominant, 10-30 x 6-10 µm, ovoid, ellipsoid or clavate, internally developing a very thick mucilaginous wall leaving a narrow lumen. Hymenophoral trama subregular, hyaline, subgelatinized, of loosely woven refractive hyphae, 2-8 µm diam., with a thin or thickened wall. Subhymenial layer 10-22 µm wide, pseudoparenchymatous, conspicuous. Peridiopellis a repent epicutis, about 40 µm thick, of narrow hyphae, 3-6 µm diam., with a pale brown wall, heavily encrusted with reddish brown granules; also present numerous, amorphous, brown pigmented bodies.

Rhizopogon rubescens, in addition to R. luteolus, has also been introduced into Australia with Pinus. According to Cunningham (1944: 45) it occurs abundantly with Pinus radiata with which it forms a mycorrhizal association in both Australia and New Zealand. The rhizomorphs tend to be less conspicuous than in R. luteolus and the gleba is not so gelatinized so that it may be easily sectioned when dry.
Considerable confusion still exists in the literature over the correct name for this species. Svrcek (1958: 130) included R. rubescens under the name R. roseolus (Corda) T. M. Fries, whilst Lange (1916: 53) maintained that there were two species in Europe, R. rubescens with spores 6.7-9.5 x 2.6-3.2 µm, and R. roseolus with spores 8-10.5 x 3.5 4.5µm. Smith & Zeller (1966: 88) recognized differences in gasterocarp pigmentation between the two species.

Type: Mycorrhizal Fungi; Description: Basidiomata hypogeous to subepigeous, irregularly globose, white at first then lemon yellow, tinged red when bruised, up to 60 mm in diameter, with weakly developed rhizomorphs; peridium composed of a single layer, yellowish brown in section. Gleba firm, reddish brown to greyish brown; tramal plates enclosing subglobose empty locules. Basidiospores elliptical, 0-septate, 6–9 × 3–4 μm, smooth, pale yellow.

Distribution: Northland, Auckland, Coromandel, Waikato, Bay of Plenty, Taupo, Wanganui, Gisborne, Hawkes Bay, Nelson, Buller, Westland, North Canterbury, Mid Canterbury, Dunedin, Southland.; 1st Record: Chu-Chou (1979).

Significance: Isolated from and experimentally shown to be a mycorrhizal partner of Pinus radiata (Chu-Chou 1979). It is the fungus most commonly isolated from mycorrhizal roots of P. radiata seedlings and young (<5-year-old) trees and is regarded as a major mycorrhizal partner. Seedlings inoculated with R. rubescens were found to be significantly larger than seedlings inoculated with Endogone flammicorona (Chu-Chou & Grace 1984) or with Laccaria laccata and Hebeloma crustuliniforme (Chu-Chou & Grace 1985) at the end of the first growing season.; Host(s): Pinus radiata.