Inocybe avellaneorosea Esteve-Rav., E. Larss. & Pancorbo, sp. nov.

Index Fungorum number: IF 900464; MycoBank number: MB 900464; Facesoffungi number: FoF 14220; Fig. 1

Etymology – Referring to the colour of the pileus (from Latin “avellaneus” which refers to the hazelnut colour of the pileus) and the stipe (from Latin “roseus” which refers to the pink or rosy tone of the stipe).

Diagnosis – Inocybe avellaneorosea is close to I. oblectabilis (Britzelm.) Sacc. in morphological and ecological characters. It differs macroscopically by the conspicuous and persistent pink to rosy tone along the entire length of the stipe of fresh and young basidiomes (except bulb), the slightly shorter pleurocystidia on average (Lm=47 µm vs. 52.5 µm) and the spores with a slightly higher Qm (1.3 µm vs. 1.25 µm), provided with a lower number of nodules (11–15 µm vs. 14–18 µm), these being slightly higher and gently tapered towards their apex. Both species also differ in their molecular characters in the ITS sequence (90% similarity).

Macromorphology – Basidiomata agaricoid and stipitate. Pileus 15–25(–30) mm, at first conical-campanulate, then convex to plano- convex, broadly obtuse umbonate to subumbonate, matt, not or hardly hygrophanous; margin straight, regular to wavy with age, fissurate at times; velipellis present at the umbo, usually poorly developed and persistent, at least in young specimens; colour uniformly brownish, rarely slightly lighter towards the margin, from chestnut brown to hazelnut brown (Mu 7.5YR 5/6-8, 4/4-6); surface radially fibrous, smooth, tending to become slightly rimose towards the margin, in older specimens sometimes broken into shreds and longitudinally frayed, greasy in appearance when moist. Lamellae crowded (L=48–60; l=1), free to almost free, ventricose, initially white, becoming ochraceous to pale brown, then tobacco brown, edge concolourous to slightly paler in
adult specimens, finely crenulate. Stipe 25–40 × 3–5 mm, straight, abruptly bulbous, bulb clearly marginate [6–8(- 10) mm broad]; colour typically pinkish (rosé) over its entire length when young and fresh (Mu 5YR 7/2-4), only slightly paler towards the base, then brownish-pink with age or when dry, white in the bulb; surface densely pruinose along the entire surface, pruina sparser towards the base in some specimens. Cortina absent. Context fibrose, dirty whitish at the pileus, uniformly pinkish along the stipe, white in the bulb. Smell not significant when cut, taste not recorded. Colour of exsiccatum uniformly tobacco brown (pileus and stipe), not blackening.

Micromorphology – Spores (7.7–)8–9.2–10.6(–11.5)×(5.6–)6–7–8(–8.7) µm, Q =(1.02–)1.12–1.3–1.53(–1.63) (n = 232 from 3 coll.), mostly subisodiametric to sometimes subheterodiametric, nodulose under the optical microscope, provided with 11–15 distinct knobs variable in height (≈1 µm high), yellowish, apicula distinct. Basidia (23.7–)24–27.1–31(–32.1) × (8.2–)8.5–9.9–11. 2(–11.3) µm; Q = (2.27–)2.3–2.7–3.01(–3.06), 4-spored, rarely 2-spored, clavate. Pleurocystidia abundant, (30 .5–)38.2–47–55.2(–69.2) × (11.7–)14.3–18.1–20.8(–27. 3) µm. Q =(1.56–)2.04–2.6–3.18(–3.52), (n=100 from 3 coll.), broadly fusiform, hyaline, base often attenuate but not pedicellate, rather crystalliferous at the apex, walls (0.99–)1.07–1.4–1.85(–2.03) µm thick, reaching − 2.8 µm at the apex, hyaline in 10% NH4OH. Lamella edge practically sterile, composed by numerous protruding hyaline cheilocystidia mixed with abundant hyaline clavate paracystidia. Cheilocystidia numerous, (28.7–)31–42.4– 52.3(–55.3) × (10.8–)12.2–16.8–20.9(–24.8) µm, Q = (1.23–)1.64–2.5–3.42(–4.23), from globose-pyriform to fusiform to subcylindrical, some with brownish intracellular contents. Hymenophoral trama regular to subregular, consisting of parallel hyphae, 4.9–11.2 μm wide, cylindrical to subfusiform in shape, often constricted at the septa, hyaline. Subhymenium poorly developed, consisting  of 2–3 layers of small, sub-isodiametric, irregular cells, (5.6–)6.0–7.7–9.7(–10.1) μm diam. Pileipellis a cutis consisting of parallel cylindrical cells, 5–11 µm wide, with finely encrusting brown- yellowish pigment; subcutis with paler and wider elements, 10–25 µm diam., often constricted at the septa. Stipitipellis a cutis of parallel hyphae (3.6–)3.9–5.0–6.5(–6.9) µm, bearing numerous caulocystidia along the entire length of the stipe, a towards the base, (20.6–)23.8–38.9–55.3(–58.2) × (8.4–)9.2–14.5–18.7(–2 2.8) µm, Q =(1.42–)1.5–2.7–3.88(–4.51) (n=100 from 3
coll.), somewhat smaller but similar in shape to hymenial cystidia, mixed with numerous clavate to subclavate hyaline caulopara cystidia. Clamp connections abundant.

Habitat – in temperate and humid continental forests, on preferably acidic soils, under Fagaceae (Quercus, Fagus). The two studied collections from Sweden were collected in deciduous forest with Fagus, Quercus and Tilia on calcareous soil.

Geographical distribution – in continental and Mediterranean Europe, known from France, Spain, Sweden and Romania, and also Eurasia (Turkey).

Material examined – France, Corsica, Moltifao, Capannace, on the banks of the river Asco, 42.481388, 9.153611, 257 msl, in acidic soil in holm oak forest (Quercus ilex subsp. ilex), 7 November 2019, A. Altés, G. Moreno, F. Pancorbo, F. Esteve-Raventós, E. Larssson, P.A. Moreau & N. Subervielle, (AH 51879, holotype), (EL346-19, GB, isotype). Spain, Madrid province, El Escorial, Prado del Molino, Arroyo del Batán, 40.576944, − 4.134166, 915 msl, in acidic soil in oak forest (Quercus pyrenaica), 1 June 1988, M. Heykoop & F. Esteve-Raventós, (AH 23468). Navarra Foral Community, Señorío de Bértiz Natural Park, 200 msl, in acidic soil in beech-oak forest (Fagus sylvatica-Quercus robur), 26 May 2012, A. & P. Arrillaga, (Aranzadi Zientzia Elkartea/Sociedad de Ciencias Aranzadi herbarium ARANFungi, A5058255). Sweden, Västergötland, Medelplana, Råbäcks Munkängar, in soil of deciduous woods in calcareous ground, 8 August 1978, S. Jacobsson, (GB-0125617). Ibidem, in soil in deciduous woods under oaks and lime trees (Quercus robur and Tilia sp.), 8 September 2008, E. Larsson, (EL 74-08).

GenBank numbers – ITS-LSU: (AH 51879, ON994216); ITS: (EL346-19, OP002030); ITS-LSU: (AH 23468, ON994217); ITS-LSU: (A5058255, ON994218); ITS: (GB0125617, AM882898); ITS-LSU: (EL 74-08, OP002031).

Notes – The macroscopic description is based on the holotype (Fig. 1). Phylogenetically, I. avellaneorosea belongs to the clade Oblectabilis. This group is represented by I. oblectabilis (Stangl and Schwöbel 1985; Stangl 1989; Marchetti et al. 2014), with two new species, I. avellaneorosea and I. lucida which are introduced in this study (Fig. 3). These three species share many similarities in the macromorphology, such as a slender habit, pinkish tones on the stipe, the presence of a distinct marginal bulb and the hygrophanous appearance in wet condition of the pileus, which is smooth and radially fibrous, often subrimose at the margin. They also show similar preferences for the type of habitat as temperate and/or mediterranean forests of Fagaceae(Quercus sp., Fagus sp.). According to our data, I. oblectabilis is most often encountered in basic to neutral soils, whereas I. avellaneorosea and I. lucida seem to prefer acidic soils. There are also macromorphological similarities with other European species such as I. brunneorufa Stangl & J. Veselský (=I. calida Velen. s. Kuyper 1985) and I. asterospora Quél., which differ in the darker chestnut brown colours of both the stipe and pileus in young basidiomes. Also the larger cystidia and asteriform to (sub-) isodiametric spores are different in these species (Stangl 1989). Besides, the phylogenetic analysis (Fig. 149) shows that the group or clade Brunneorufa (=Calida s. Kuyper) does not support with the clade Oblectabilis, but there is a significant bootstrap support with the clade Asterospora. Inocybe avellaneorosea shows a very characteristic and conspicuous pinkish (rosy, salmon) colour throughout the stipe, especially when young, which contrasts sharply with the chestnut-brown colour of the pileus (Fig. 146). It has sometimes been confused in Europe with I. calida or I. brunneorufa (KY496805, AM882898, cited as I. calida and I. calida var. brunneorufa respectively). The size of the cystidia of I. avellaneorosea are similar to those of I. oblectabilis, although the spores are a distinguishing feature between the two, when analyzing the appearance, number and size of the nodules (Fig. 1, 2).

Figure 1 – Inocybe avellaneorosea (AH 51879, holotype). a Basidiomata in situ. b Basidiospores. c Pleurocystidia. d Cheilocystidia. e Caulocystidia at the base of stipe (mounting media: NH4OH). Scale bar: b=10 μm, c–e=50 μm, a=20 mm

Figure 2 – SEM spores of Inocybe oblectabilis epitype: a Basidiomata. b Basidiospores. Inocybe avellaneorosea holotype: c Basidiomata. d Basidiospores. Inocybe lucida holotype: e Basidiomata. f Basidiospores. Scale bar: b, d, f=2 μm

Figure 3 – Most probable tree inferred by Bayesian inference in species of Inocybe oblectabilis group based on ITS and LSU sequences. Posterior probability from Bayesian analysis/Bootstrap-ML values are shown at the branches. Thick branches indicate nodes with phylogenetic support in both analysis (posterior probability≥0.95 and bootstrap values≥95%). The tree is rooted with Pseudosperma spurium (AM882784). The country of origin of each collection is abbreviated by ISO codes, with the species types marked in bold