Hymenagaricus parvulus Al-Kharousi, Al-Sadi, Al-Yahya'ei , & S. Hussain, 2024

Hussain, Shah, Al-Kharousi, Moza, Al-Maqbali, Dua'a, Al-Owaisi, Arwa A., Velazhahan, Rethinasamy, Al-Yahya'ei, Mohamed N. & Al-Sadi, Abdullah M., 2024, Two new species of Hymenagaricus (Agaricales, Agaricaceae) from Oman, based on morphology and molecular phylogeny, MycoKeys 105, pp. 1-19 : 1

Hymenagaricus parvulus Al-Kharousi, Al-Sadi, Al-Yahya'ei, & S. Hussain sp. nov.

Figs 5 , 6 , 7

Diagnosis.

The new species Hymenagaricus parvulus can be differentiated from other species of the genus by its small-sized, creamy basidiomata, umbonate pileus covered with appressed pellicle.

Holotype.

Sultanate of Oman: Dhofar, Salalah, Wadi Jarzeez, on termite mounds, under the trees of Anogeissus dhofarica , 8 August 2022, S. Hussain, A. Al-Owaisi, Al-Yahya’ei & Al-Sadi, JRZ-22-004 (holotype Mawarid-JRZ-22-004), GenBank accession: ITS = OR612994, 28S = OR613017, EF-1α = OR735176.

Etymology.

The specific epithet ' parvulus ' refers to the small-sized basidiomata of the new species.

Description.

Basidiomata small-sized. Pileus 15-25 mm in diam., at young stage globose to parabolic, surface floccose squamulose, squamules light pinkish to creamy, with appressed pellicle at the centre, margin appendiculate; at mature stage cap convex to hemispherical with the broadly umbonate disc, with appressed, pale brownish pellicle at the disc, surface finely floccose squamulose, squamules pale creamy to light greyish, margins striate, just exceeding the lamellae; context membranous, pinkish on cutting. Lamellae free, pale pinkish to brownish, ventricose, sparsely crowded, with 1-2 series of lamellulae. Stipe 25-35 × 2-5 mm, equal, annulus cortinate, concolorous to squamules; stem surface creamy, covered with finely floccose squamules below the annulus, smooth above the annulus, context pinkish on cutting, fistulose. Smell pleasant. Taste not recorded.

Basidiospores 5.0-6.5 × 4.0-4.5 µm, average size 6.0 × 4.2 µm, Q = 1.3-1.5, av. Q = 1.4; ellipsoid to broadly ellipsoid, yellowish to dark brown, smooth, thick-walled, apiculus visible, germ-pore not observed. Basidia 16.5-22.5 × 6.5-8.5 µm, on average 19.0 × 7.5 µm, clavate to cylindrical, smooth, hyaline in KOH, tetrasporic. Cheilocystidia 19-25 × 9-11 µm, on average 22 × 10 µm, clavate to broadly clavate, often turning to one side, with multiseptate base, smooth, thin-walled, hyaline in KOH. Pleurocystidia absent. Subhymenium consisting of cylindrical to elongated cells, measuring 6-9 µm diam. Pellicle is a hymeniform, consisting of chains of several elements, each element measuring 14-22 × 12-17 µm, globose to subglobose or ovoid, hyaline or pale yellowish, smooth, thin-walled; these chains of elements attached to inflated hyphae with encrusted walls. Veil is a cutis to ixocutis, consisting of elongated or cylindrical elements, not easily detached, hyaline, thin-walled, with terminal element fusiform with papillate end, each element measuring 15-18 × 5-7 µm. Annulus is an intricate trichoderm, composed of hyaline hyphae, 4-7 µm diam., cylindrical, constituted by short elements, constricted at septa and easily disarticulated. Clamp connections absent in all tissues.

Habit, habitat and distribution.

Fruiting body formation occurs in early August to early September, saprotrophic, scattered in small groups, found on termite mounds. Currently only known from southern Oman.

Additional specimens examined.

Sultanate of Oman: Dhofar, Salalah, Wadi Jarzeez , on termite mounds, under the trees of Anogeissus dhofarica , 11 August 2022, S. Hussain, A. Al-Owaisi, Al-Yahya’ei & Al-Sadi, JRZ2-22-002 (Mawarid-NHZ-22-002), GenBank accession: ITS = OR612995 .

Notes.

Hymenagaricus parvulus is a small, cream-coloured species, differentiated from other species of the genus by its whitish to pale pinkish floccose squamules on pileus and stipe surfaces with a broadly umbonate centre. Hymenagaricus parvulus shares basidiomata size and basidiospores morphology with H. pakistanicus . However, H. pakistanicus can be differentiated from the new species by its caesptiose fruiting habit, pileus with pinkish to brownish squamulose pellicle, consisting of pseudoparenchymatous cells ( Syed et al. 2023). Hymenagaricus saisamornae differs from the new species by its smaller pileus (up to 15 mm diam. Vs. 15-25 mm of H. parvulus ), covered with brownish pellicles and larger basidiospores (5.5-7.0 × 4-4.5 µm; Kumla et al. (2021)). Hymenagaricus siamensis , another small-sized species is distinguished from the new species by its pinkish-brown cap, pellicle comprised of pseudoparenchymatous cells and larger basidiospores (6.5-8.0 × 4.0-5.0 µm; Kumla et al. (2023)). Similarly, Hymenagaricus canoruber (Berk. & Br.) Heinem. & Little Flower, known from India and Sri Lanka, is characterised by a small-sized pileus (15-25 mm diam.), with greyish-brown squamules, hymeniform pellicle and smaller basidiospores (4.6-5.7 3.5-4.3 µm; Heinemann and Little Flower (1984)). Hymenagaricus pallidodiscus D.A. Reid & Eicker, the smallest mushroom in the genus with pileus diam. up to 11 mm, covered with brownish squamules and smaller basidiospores (4.2-5.4 × 3.1-3.8 µm; Reid and Eicker (1999)). Hymenagaricus cylindrocystis Heinem. & Little Flower another small-sized species, has been reported in Singapore and India, with a brownish cap, larger basidiospores (6.4-8.4 × 4.5-5.6 µm) and a pseudoparenchymatous pellicle ( Heinemann 1956; Heinemann and Little Flower 1984). Hymenagaricus cf. kivuensis and H. wadijarzeezicus with their medium-sized pilei can be easily differentiated from H. parvulus .

Figures

Figure 5. Basidiomata of Hymenagaricus parvulus (based on holotype collection JRZ- 22 - 004) A mature and young basidiomata B mature basidimata.

Figure 6. Light microscopy of anatomical features of Hymenagaricus parvulus (based on holotype collection JRZ- 22 - 004) A basidiospores B basidia C cheilocystidia D annulus E pellicle structure F veil elements. Scale bars: 5 µm (A); 10 µm (B, C); 15 µm (D-F).

Figure 7. Line drawings of anatomical features of Hymenagaricus parvulus (based on holotype collection JRZ- 22 - 004) A basidiospores B basidia C annulus elements D cheilocystidia E pellicle structure F veil elements. Scale bars: 5 µm (A); 10 µm (B, D); 15 µm (C, E, F).