Typification: OAHU, HAWAII, USA: Manuwai Gulch, 485 m, 16 May 2014, J. Hayward R11O (holotype HAW-F-00086).
Etymology: The specific epithet “kualapa” is the Hawaiian term for a ridge and refers to this species’ intervenose ridges.
Basidiomata solitary or scattered, with convex pileus in immaturity, maturing planoconvex or rarely depressed, 24-55 mm in diameter, sometimes umbonate, pileipellis minutely hispid in immaturity, maturing glabrous, in maturity viscid to glutinous when wet, gray-brown (N7 to 5P 7/6, 10R 7/4 or 10RP 6/4), margin with weak tuberculate striations, becoming more pronounced in maturity, inflexed in immaturity. Lamellae free, up to 4 mm in depth, subdistant (12-15/cm circumference at margin), forking once near margin, intervenose, with hymenium covering interveinations and interlamellate trama, lamellulae absent. Stipe cavernate, densely and minutely hispid, especially in immaturity, progressively less hispid with age, gray (N6 to 10RP 6/4), at maturity 12-23 mm in height, 6-12 mm in diameter, cylindrical or slightly broader at apex.Odor faintly of benzaldehyde, strongly of benzaldehyde while drying. Taste mild; spore print white.
Spores (6.51) 6.8-7.09-7.33 (7.45) µm × (7.5) 7.84-8.03-8.28 (8.44) µm, Q=(1.09) 1.11-1.13-1.17 (1.2), ellipsoid, ornamentation composed of warts, more or less isolated but with occasional low line-connections, hilum 1.7-2.4 µm in length, only ornamentation displaying an amyloid reaction in Lugol’s iodine; Basidia 45-54 µm in length, 10-13 µm in diameter, nearly cylindrical, 4-spored, with sterigmata 5.7-7.6 µm in length, 1.5-1.85 µm in diameter at base; basidiolesnearly cylindrical to almost sphaeropedunculate, 7.4-10.9 µm in diameter, 35.4-58.8 µm in length; Marginal cells poorly differentiated from basidioles,clavate to sphaeropedunculate, 7.3-11.5 µm in diameter at widest point, 29.3-37.7 µm in length. Pleurocystidia, cheilocystidia absent.
Lamellartrama composed of small, tightly-packed sphaerocytes, 8-24 µm in diameter, with occasional uninflated hyphae 4-7 µm in diameter. Subhymeniumwith abundant, tightly-packed sphaerocytes 11-44 µm in diameter and rare uninflated elements 2.8-3.8 µm in diameter, nearly pseudoparenchymatic.Pileipellis two-layered, distinct from underlying context; suprapellis 59-87 µm deep, a slightly gelatinized trichodermium consisting of cylindrical, vertically-oriented hyphae 2.8-3.8 µm in diam, occasionally interwoven; ciliate dermatocystidia frequent in immaturity, occasional or absent at maturity, with subterminal elements 4-6 µm in diameter and up to 15 µm in length; terminal elements up to 24 µm in length and Stipitipellis 90-200 µm in depth, pigmented, with capitulate caulocystidia, 38-62 µm in length, 4.9-6.5 µm in diameter; capitulum 1.3-2.4 µm in diameter. Clampconnections absent in all parts.
Comments: Of the Pisonia sandwicensis-associating fungi described here, this species apparently fruits the least frequently. In our experience it is most common on Oahu October-November. The benzaldehyde-like odor, cavernate stipe, gelatinized pellis, and somewhat striate margin suggest placement in subsection Foetentinae (Melzer & Zvára) Singer of subgenus Ingratula Romagn. Its most distinctive field characters of this species include its intervenose lamellae, weak benzaldehyde odor, mild taste, and minutely hispid stipe. Amongst described Russula species, this species is most reminiscent of Russula venezueliana Singer and R. ochrostraminea Pegler. It shares many microscopic and macroscopic features with both species. Both R. venezueliana and R. ochrostraminea may also associate with Nyctaginaceae species (Pegler & Singer, 1980; Buyck & Ovrebo, 2002). However, R. venezueliana has smaller spores, while R. ochrostraminea lacks the benzaldehyde odor typical of R. kualapa.
Specimens examined: KAUAI, HAWAII, USA: Puu Ka pele Forest Reserve, 885m, 30 June 2015: Hayward R1K; OAHU, HAWAII, USA: Mokuleia Forest Reserve, 336 m, 12 April 2015: Hayward R7O; OAHU, HAWAII, USA: Mokuleia Forest Reserve, 400 m, 18 October 2015: Hayward R12O; OAHU, HAWAII, USA: Mokuleia Forest Reserve, 400 m, 7 March 2015: Hayward R15O.