Lactarius cucurbitoides H. Lee & Y.W. Lim, 2015

Lee, Hyun, Park, Myung Soo, Jung, Paul Eunil, Fong, Jonathan J., Oh, Seung-Yoon, Verbeken, Annemieke & Lim, Young Woon, 2015, Lactarius cucurbitoides (Russulales, Basidiomycota), a new species from South Korea supported by molecular and morphological data, Phytotaxa 205 (3), pp. 168-176 : 172-174

Lactarius cucurbitoides H. Lee & Y.W. Lim , sp. nov. ( Figs. 2 & 3 )

MycoBank: MB 809952

Diagnosis: Lactarius cucurbitoides differs morphologically from the closely related species of L. subg. Plinthogalus by non-discoloration of the white latex when exposed to air.

Type:— SOUTH KOREA. Gyeongsangbuk-do, Sangju-si, Seongjubong Natural Recreation Forest, 233 m elev., N36°32’02” E128°02’29”, 19 July 2013, SFC20130719-110 (Holotype, SFC!)

Pileus 30–60 mm in diam., first convex, then plane, finally with slightly uplifted margin and concave center; surface dry, very delicately appressed subtomentose when young, with age becoming rugose to rugulose, evenly pale yellow (4A3) to pale orange (6B3) when old. Stipe 30–50 mm long, 7–10 mm broad, uniform, regular; surface dry, pubescent, white, slightly staining pinkish or unchanging when bruised; context first solid, then hollow. Lamellae decurrent to adnate, 3–7 mm broad, distant, with 2–3 series of lamellulae, greyish orange (6B4) when young, darker (6B6) with age, slowly staining pinkish when bruised; edges even. Context in pileus white, up to 7.5 mm thick at the center, slowly changing pale pinkish on exposure in pileus. Latex white, abundant; taste acrid. Spore print white or creamy.

Basidiospores globose to subglobose, 7.0–8.4 (8.8) × (6.4) 6.8–8.0 (8.2) μm (Q = 1.02–1.12(1.13), n = 20); ornamentation amyloid, made up of broad, quite irregular and little sharp ridges, locally up to 2.2 μm in height; ridges often with a paternoster-like (string of beads) aspect, as if made up of several verrucae, forming a fragmentary reticulum, with some helically arranged aspect; isolated verrucae and fragmented ridges abundant. Basidia narrowly clavate to subcylindric, 48.1–59.7 × 11.0–15.6 μm, 4-spored; sterigmata 6.5–9.3 × 2.0–3.1 μm. Pleuromacrocystidia absent. Pleuropseudocystidia abundant, sometimes diverging toward top, usually spherical on top, 3.8–7.2 μm in diam. broad, with refractive and guttate content. Lamellar edge sterile; marginal cells generally cylindric, 13.5–26 × 3–6 μm. Hymenophoral trama filamentous, septate, transparent hyphae, 2.5–3.2 μm wide and numerous lactiferous hyphae, 7–13 μm wide. Pileipellis a 60–70 μm thick trichopalisade, consisting of interwoven hyphae; tip of elements cylindric, 11.5–19 × 4.2–6.8 μm. Stipitipellis a trichoderm, 40–80 μm thick; thin walled hyphae, 11.4–25.6 × 4.0–6.3 μm. Clamp connection absent.

Habitat: —Solitary or sparse on ground in deciduous forest dominated by Quercus spp.

Etymology: —Referring to the pileus shape being similar to a pumpkin.

Additional studied material: — SOUTH KOREA. Gangwon-do , Wonju-si, Chiak National Park, 496 m elev., N37°16'36" E128°4'47", 18 August 2011, SFC20110818-21 (Paratype SFC!) ; Ibid., 505 m elev., N37°16'37" E128°4'52", 25 August 2011, SFC20110825-14 (Paratype SFC!) .

Comment: —The pale yellow (4A3) to pale orange (6B3) color of the pileus and non-discoloration of white latex are characteristics of L. cucurbitoides that distinguish it from other taxa in the subgenus Plinthogalus . Although phylogenetically closely related to L. subplinthogalus , L. friabilis , and L. oomsisiensis , L. cucurbitoides can be distinguished from these species by color change of context: L. cucurbitoides has relatively pale discoloration of context and unchanged color of latex when bruised, whereas the other three species has pinkish like discoloration of the exposed context and latex. Microscopically, L. cucurbitoides has slightly larger spores and much shorter basidia compared to L. oomsisiensis . For the comparison of L. cucurbitoides and two Asian species with similar morphology, L. montoyae and L. subplinthogalus var. chiangmaiensis , L. cucurbitoides had smaller, less ornamented spores compared to L. montoyae and a relatively larger fruit body compared to L. subplinthogalus var. chiangmaiensis . Despite a slightly pale color compared to L. oomsisiensis , the dark lamellae of L. cucurbitoides are also striking in character.

Figures

FIGURE 2. Fruit body of Lactarius cucurbitoides (SFC20130730-110, holotype): (a) surface of pileus and (b) lamellae with white latex.

FIGURE 3. Microscopic features of Lactarius cucurbitoides (SFC20130719-110, holotype): (a) basidiospores (SEM), (b) basidia, (c) pleuropseudocystidia, (d) pileipellis, and (e) marginal cells.