Xylochrysis aquatica J.Y. Song & X.D. Yu

Song, Jing-Yi, Yang, Yi, Yu, Xian-Dong, Dissanayake, Asha J. & Tian, Qing, 2023, Xylochrysis aquatica sp. nov. (Woswasiaceae) from freshwater habitats in Sichuan Province, China, Phytotaxa 587 (1), pp. 31-38 : 34-35

Xylochrysis aquatica J.Y. Song & X.D. Yu sp. nov. ( FIG. 2 )

MycoBank: MB844596

Etymology: In reference to the aquatic habitat of the fungus

Holotype: HKAS 124019

Saprobic on submerged decaying wood in a freshwater stream. Sexual morph: Ascomata 160–265 µm diam. × 145– 290 µm high ( x = 200 µm × 205 µm, n = 10), solitary, scattered, immersed to slightly erumpent, globose to subglobose, nonstromatic, uniloculate, glabrous, without a golden yellow layer of surrounding cells at the basal venter, ostiolate. Ostiole 65–135 µm long, 65–130 µm diam. ( x = 108 µm × 96 µm, n = 10), black, papillate, glabrous, shiny, lined with hyaline periphyses. Ascomatal wall multi-layered, outer layers 12–47 µm thick, composed of brown to dark brown cells of textura angularis, carbonized and form a thicker layer in the lower part of the ostiole, inner layers 13–33 µm, comparatively thick, composed of flattened, hyaline cells of textura prismatica. Hamathecium 2.5–5.0 µm wide ( x = 4.0 µm, n = 30), comprising numerous, narrowly cylindrical to filiform, branched, septate paraphyses, not embedded in a gelatinous matrix. Asci 68–120 µm × 3.0–6.5 µm ( x = 96.0 × 4.5 µm, n = 30), 8-spored, unitunicate, cylindrical, long pedicellate, tapering to the bulbose base, apically rounded with an apical ring. Ascospores 4.5–6.5 µm × 2.5–4.0 µm ( x = 6.0 × 3.0 µm, n = 30), L/W 1.5–2.5 ( x = 2.0, n = 30), uniseriate, ellipsoidal, hyaline, aseptate, straight, 2-guttulate, thin-walled, smooth-walled, without mucilaginous sheath or appendages. Asexual morph: Undetermined.

Culture characteristics: Ascospores germinated on PDA within 24 hours, and germ tubes were produced from both ends of the ascospores. Colonies growing on PDA reaching a diameter of 20 mm after 24 days at 25 °C, rough, irregular, slightly raised, edge crenate, with both surfaces dark-gray in the margin and grayish-white towards the center, slowly growing, reverse taupe brown, without sporulation.

Material Examined: CHINA, Sichuan province, Chengdu, Pengzhou county, Huilonggou Scenic Area , ( 31°14′21″ N, 103°47′28″ E), on a submerged decaying wood of undetermined host, 28 July 2021, Xian-Dong Yu ( HKAS 124019 , holotype; HUEST 22.0028, isotype); ex-type culture CGMCC 3.23639 (= UESTCC 22.0030 ) .

Notes: Xylochrysis aquatica fits well with the morphological characteristics of Xylochrysis in having globose ascomata, numerous paraphyses, cylindrical and long pedicellate asci, ellipsoidal and hyaline ascospores ( Réblová et al. 2014). Xylochrysis aquatica is easily distinguished from the type species X. lucida by solitary, scattered, smaller ascomata (160–265 µm × 145–290 µm vs. 350–500 µm × 350–500 µm) without a layer of colored cells surrounded, longer asci (60–120 µm long vs. 59–73 µm long) and more rounded ascospores (L/W: 1.5–2.5 µm vs. 2.2–2.8 µm). Ascomata of X. lucida often aggregated or confluent in groups of 3–10 and surrounded by a golden yellow layer of cells. In addition, the ostiolar neck of X. lucida is short-beaked and distinctly longer ( Réblová et al. 2014) than our new taxon, X. aquatica . The multi-gene (ITS-LSU-SSU- tef1-α -rpb2) phylogenetic analyses suggested that our isolate clustered together with the generic type X. lucida and formed a distinct lineage (100% ML; 1.00 PP) in Woswasiaceae . In addition, a nucleotide comparison of X. aquatica (CGMCC 3.23639) and X. lucida (CBS 135996) revealed 25 basepair (5 %) and 70 base-pair (7.2 %) differences in ITS (+ 5.8S) and rpb2, respectively ( TABLE 2 ). Xylochrysis aquatica is introduced as a new species based on the moprhology and phylogeny evidences.

Figures

FIGURE 2. Xylochrysis aquatica (HKAS 124019, holotype) a, b Appearance of ascomata on the host surface. c Vertical section of ascomata. d Ostiole. e Vertical section through ascomatal wall. f Hamathecium. g Apical ring stained with Lugol’s iodine reagent. h–l Asci. m–o Ascospores. p Germinating ascospore. q Colony from above. r Colony from below. Scale bars: c, d = 50 μm, e, f, h–l = 20 μm, p = 10 μm, g, m–o = 5 μm.