Three new species of Aleurodiscus s.l. (Russulales, Basidiomycota) from southern China

Abstract Three new species of Aleurodiscus s.l. with corticioid basidiomata are described and illustrated from southern China based on morphological evidence and phylogenetic analyses of ITS and nrLSU sequence data. Aleurodiscusbambusinus was collected from Jiangxi Province on bamboo and is distinct by having a compact texture, simple-septate generative hyphae, abundant acanthophyses, basidia with acanthophysoid appendages and smooth basidiospores. Aleurodiscusisabellinus was collected from Yunnan Province on both angiosperm wood and bamboo and is distinct by having soft basidiomata with yellow to yellowish-brown hymenophore, yellow acanthophyses, simple-septate generative hyphae and smooth basidiospores. Aleurodiscussubroseus was collected from Guangxi Autonomous Region and Guizhou Province on angiosperm wood and is distinct by having pinkish basidiomata when fresh, clamped generative hyphae, clavate acanthophyses and echinulate basidiospores. In the phylogenetic tree, A.bambusinus and A.isabellinus were nested within the A.cerussatus group, whilst A.subroseus was clustered with A.wakefieldiae. An identification key to 26 species of Aleurodiscus s.l. in China is provided.


Introduction
Aleurodiscus s.l. is a large group of wood-inhabiting fungi with a broad morphological circumscription. It is characterised by having cupulate, effused or effused-reflexed basidiomata, a monomitic or dimitic hyphal system with simple-septate or clamped gen-erative hyphae, smooth or ornamented, amyloid basidiospores and sterile organs such as acanthophyses, gloeocystidia and dendrohyphidia (Núñez and Ryvarden 1997). Although Aleurodiscus s.l. had been divided into several small genera based on different combinations of morphological characters, phylogenetic analyses did not fully support these separations (Wu et al. 2001;Dai and He 2016). Accordingly, the inter-and intrageneric phylogeny of Aleurodiscus s.l. in Stereaceae is still unclear and no reliable morphological characters can be used to recognise the small segregated genera. Thus, the broad sense concept of the genus has often been adopted by mycologists when describing new species (Núñez and Ryvarden 1997;Gorjón et al. 2013;Dai et al. 2017a, b).
A recent survey on Aleurodiscus s.l. from China (Dai and He 2016, 2017, Dai et al. 2017a revealed that its species diversity is high and many species, especially those with corticioid basidiomata on both herbaceous and ligneous plants, are still undescribed. In the present study, three new species are described and illustrated from southern China, amongst which two species have abundant acanthophyses and smooth basidiospores and one species bears echinulate basidiospores. Morphological differences between new species and their relatives are discussed. Their phylogenetic positions were inferred from a combined dataset of ITS and nrLSU sequence data.

Morphological studies
Voucher specimens are deposited in the herbaria of Beijing Forestry University, Beijing, China (BJFC), Centre for Forest Mycology Research, U.S. Forest Service, Madison, USA (CFMR) and Southwest Forestry University, Kunming, China (SWFC). Freehand sections were made from basidiomata and mounted in 2% (w/v) potassium hydroxide (KOH), 1% phloxine (w/v) or Melzer's reagent. Microscopic examinations were carried out with a Nikon Eclipse 80i microscope at magnifications up to 1000×. Drawings were made with the aid of a drawing tube. The following abbreviations are used: L = mean spore length, W = mean spore width, Q = L/W ratio, n (a/b) = number of spores (a) measured from number of specimens (b). Colour names and codes follow Kornerup and Wanscher (1978).

DNA extraction and sequencing
A CTAB plant genome rapid extraction kit-DN14 (Aidlab Biotechnologies Co. Ltd, Beijing) was employed for DNA extraction and PCR amplification from dried specimens. The ITS and nrLSU gene regions were amplified with primer pairs ITS5/ITS4 (White et al. 1990) and LR0R/LR7 (http://www.biology.duke.edu/fungi/mycolab/primers.htm), respectively. The PCR procedures followed Dai and He (2016). DNA sequencing was performed at Beijing Genomics Institute and the sequences were deposited in GenBank.
Additional Remarks. All the studied specimens of A. isabellinus lack a true hymenium and only the holotype has a few basidia and basidiospores. Aleurodiscus isabellinus was nest- ed within the A. cerussatus group (Fig. 1). In this group, Aleurodiscus thailandicus S.H. He is similar to A. isabellinus by sharing the yellow basidiomata and acanthophyses, but differs by having two types of gloeocystida and acanthophyses without a clavate or cylindrical base (Dai et al. 2017a). The ITS similarity between A. isabellinus (He 5283) and A. thailandicus (He 4099) is 93.6% of 578 base pairs. Aleurodiscus thailandicus was described from Thailand based on a fertile specimen on bamboo, but later several sterile specimens on bamboo from south-western China were identified as this species according to the sequence data. Morphologically, the soft and yellow to yellowishbrown basidiomata of A. isabellinus resemble the genus Vararia P. Karst. which belongs to Peniophoraceae according to phylogenetic analyses. Etymology. "Subroseus" (Lat.) refers to the pinkish basidiomata when fresh. Basidiomata. Annual, resupinate, effused, closely adnate, inseparable from substrate, coriaceous, at first as small irregular patches, later confluent up to 35 cm long and 3 cm wide, up to 300 μm thick. Hymenophore smooth, pinkish-white (12A2), pink (12A3), pale orange (6A3) to light orange (6A4) when fresh, becoming pale orange (6A3), light orange [6A(4-5)], greyish-orange [6B(3-6)] to brownish-orange [6C(5-6)] when dry, uncracked; margin abrupt, white and distinct when fresh, becoming concolorous or darker than hymenophore and indistinct when dry, slightly elevated when mature.