Serendipita officinale sp. nov. (Serendipitaceae): a new species of orchid mycorrhizal fungus Author Wang, Xin-Ju 0000-0001-5337-9614 Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming, Yunnan 650500, China. 1247849502@qq.com Author Li, Neng-Qi 0009-0000-7751-0509 College of Landscape Architecture and Horticulture Sciences, Southwest Forestry University, Kunming, Yunnan 650224, China. 632514709@qq.com Author Gao, Jiang-Yun 0000-0003-1541-5922 Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming, Yunnan 650500, China. jiangyun.gao@ynu.edu.cn text Phytotaxa 2023 2023-12-20 630 3 229 240 https://phytotaxa.mapress.com/pt/article/download/phytotaxa.630.3.4/51378 journal article 10.11646/phytotaxa.630.3.4 1179-3163 10410012 Serendipita officinale X. J. Wang , sp. nov . ( Fig. 1 ) MycoBank MB809112 Diagnosis. Differs from other Serendipita species by abundant villiform and felty aerial mycelium, uninucleate hyphal cells, and the highest growth rate in terms of colony diameter. Type. China . Chongqing Province : Wanzhou District , Luotian town , isolated from protocorms and adult roots of Dendrobium officinale , 30°31′N , 108°33′E , 1200 m , alt., Sept. 2018 ( holotype HMAS 352471 ; ex-type culture CCTCC M 2019744 ; GenBank MN173026 ) . Etymology. officinale , referring to the plant species, D. officinale from whose protocorms and adult roots the species was first collected. Description. The fungal colony reaching 78 mm in diam. on PDA medium at 25 °C in the dark after two weeks. The cultures are a cream to pale yellow in color with a circular or nearly circular growth habit; formed a rough, appressed, waxy, thick and moist layer with radial streaks near the edge; submerged mycelium was observed ( Fig. 1a ). After one month, abundant villiform and felty aerial mycelium in white could be observed in intermediate zone ( Fig. 1b ), the emergence of aerial hyphae is clearly visible, and over time, their growth has become luxuriant ( Fig. 1c ). The hyphae were hyaline, ranging from 0.4 to 1.03 μm (0.58 ± 0.02 μm, n = 35). Hyphae elongated into arborization and often produced hyphal coils ( Fig. 1f & g ). As the hyphae aged, septate structures became evident ( Fig. 1d ), with each cell regularly containing 1 nucleus ( Fig. 1e ), but clamp connections were absent. After about four weeks of culture on PDA, the fungus produced abundant monilioid hyphae arranged in chains of more than five cells ( Fig. 1h & i ). In the inoculation treatments, the fungal strain was examined on their capacity to support seedling growth in Dendrobium officinale and D. flexicaule . Approximately six months after inoculation, Serendipita officinale showed highly positive effects on seedling growth among all treatments in D. flexicaule . In the Serendipita officinale treatment, plant height (11.78 ± 0.6 mm ) and stem diameter (2.44 ± 0.13 mm ) were significantly higher than in the asymbiotic treatment (plant height: 9.58 ± 0.35 mm ; stem diameter: 1.94 ± 0.09 mm ), as well as in other inoculated treatments which plant height ranged from 10.91 to 11.03 mm and stem diameter ranged from 2.01 to 2.32 mm (all P <0.05) (Wang et al. unpublished data). For D. officinale , after 90 days, most seedlings developed 3-5 leaves with strong roots, the percentages of seedlings (75.8 ± 2.6%) significantly higher than the percentages of the other treatments (P<0.001) ( Yang et al. 2023 ). After six months, chlamydospores (mature monilioid cells) were observed in the roots of both Dendrobium officinale ( Fig. 1j ) and D. flexicaule ( Fig. 1k ), which are globose, measuring 3–6 μm in diam, or sub-globose, measuring 3–7 × 2–5 μm. Neither conidiophores nor sexual structures were observed. Ultrastructure analysis revealed that the hyphae contained typical dolipore septa with imperforate parenthesomes ( Fig. 1l ), as the characteristic in Sebacinales . Ecology and distribution. Serendipita officinale is described from a strain isolated from protocorms and adult roots of D. officinale . Its actual geographic distribution is yet to be defined.