Rhexodenticula aquatica W. Dong, H. Zhang & Doilom, 2021

Dong, Wei, Zhang, Huang, Doilom, Mingkwan, Yu, Xian-Dong, Wang, Gen-Nuo & Nalumpang, Sarunya, 2021, Rhexodenticula aquatica (Sordariomycetidae genera incertae sedis), a novel hyphomycete from freshwater in Thailand, Phytotaxa 483 (2), pp. 129-138 : 132-135

Rhexodenticula aquatica W. Dong, H. Zhang & Doilom , sp. nov. ( FIGURE 2 )

Index Fungorum number: IF556551; Facesoffungi number: FoF 09515

Etymology:—in reference to aquatic habitat of the fungus

Holotype:— MFLU 18–1551

Saprobic on submerged wood in freshwater. Sexual morph: Undetermined. Asexual morph: Hyphomycetous. Colonies superficial, effuse, gregarious, pale brown. Mycelium mostly immersed, composed of septate, branched, pale brown, thin-walled hyphae. Conidiophores 28–35 × 3–4.5 μm (x̅ = 32 × 3.5 μm, n = 10), macronematous, mononematous, erect, subcylindrical, flexuous, 1–3-septate, slightly constricted at septa, unbranched, brown, smooth. Conidiogenous cells 18–30 × 3–3.5 μm (x̅ = 21 × 3.2 μm, n = 10), holoblastic, polyblastic, integrated, with sympodial proliferations, terminal, subcylindrical, brown, smooth. Conidia 32–37 × 4.8–5.5 μm (x̅ = 34 × 5.2 μm, n = 15), acrogenous, pleuroacrogenous, solitary, dry, thin-walled, fusiform, 3-septate, constricted at central septum, sometimes obscured at two end septa, brown to pale olivaceous, larger and slightly darker at central two cells, tapering and paler at two end cells, with rounded ends, verruculose, guttulate. Conidial secession schizolytic.

Cultural characteristics:—On PDA, colony circular, reaching 30 mm in 10 days at 25°C, surface rough, dry, with sparse mycelia, umbonate from the side view, edge entire; from above, yellowish at the margin, white to cream at the middle and centre; from below, white at the margin and middle, brown at the centre; not producing pigmentation in culture.

Material examined:— THAILAND. Songkhla Province: on submerged wood in a stream, 10 May 2018, W. Dong, 20180516-1 ( MFLU 18–1551 , holotype), ex-type living culture MFLUCC 18–1146 ; ibid., 20180516-2, ( HKAS 104999 , isotype), ex-type living culture KUMCC 19–0016 .

Notes:— Rhexodenticula aquatica clusters in Rhexodenticula with high bootstrap support and phylogenetically differs from other Rhexodenticula species ( FIGURE 1 ). Rhexodenticula aquatica differs from the type species R. cylindrospora in having brown to pale olivaceous and fusiform conidia, with larger central cells and tapered end cells ( Baker et al. 2001). In contrast, R. cylindrospora has pale brown and almost cylindrical conidia. In addition, R. cylindrospora has a narrow, basal, marginal frill, which is lacking in R. aquatica . The distinctive conidial shape of R. aquatica also differs from other two unsequenced species R. elegiae and R. zhengii in the genus (see key to species of Rhexodenticula ) ( Mel’nik et al. 2004, Li et al. 2011). Rhexodenticula species were collected from rotten leaves and dead culms in terrestrial habitat ( Baker et al. 2001, Mel’nik et al. 2004, Li et al. 2011, Klaubauf et al. 2014, Crous et al. 2016), while our new species R. aquatica was collected from submerged wood in freshwater habitat. Both phylogenetic analysis and morphological comparison support R. aquatica to be a new species in Rhexodenticula ( FIGURE 1 ).

Figures

FIGURE 1. RAxML tree generated from combined LSU, SSU, ITS and TEF sequence data analysis. Bootstrap support values for maximum likelihood (the first value) equal to or greater than 75% and Bayesian posterior probabilities (the second value) equal to or greater than 0.95 are given above or below the nodes. The tree is rooted to Aureobasidium pullulans CBS 584.75 and Dothidea insculpta CBS 189.58. The ex-type strains are indicated in bold and newly introduced taxon is indicated in red.

FIGURE 2. Rhexodenticula aquatica (MFLU 18-1551, holotype) a Colonies on submerged wood. b Conidiogenous cell with conidium. c Conidiophore. d, e Conidiogenous cells. f–j Conidia. Scale bars: b, c, f–j = 15 μm, d, e = 5 μm.