Natantispora unipolaris K.L. Pang, S.Y. Guo & E.B.G. Jones.
Index Fungorum number: IF551074; Facesoffungi number: FoF00564; Fig. 2
Etymology: In reference to the unipolar ascospore appendage.
Holotype: F27870 (National Museum of Natural Science, Taiwan)

Saprobic on dead stems. Sexual morph Ascomata 78–(124)–158×75–(119)–216μm (n=9), light to dark coloured when mature, globose to subglobose, solitary or gregarious, immersed, coriaceous, ostiolate. Necks 30–(59)– 96μm long (n=8), periphysate. Peridium 5–33μm (n=18), composed of one layer of elongated cells with large lumina, cells of textura angularis. Catenophyses present, persistent. Asci 59–(87)–108×15–(18)–20μm (n=8), 8-spored, unitunicate, clavate, thin-walled, persistent, short pedicellate, developing from inner wall of ascoma base, no apical apparatus or retraction of plasmalemma. Ascospores 21–(25)–28×6–(8)–8μm (n=50), elongate-ellipsoidal, hyaline, 1-septate, not constricted at the septum. Appendages unipolar, initially adpressed to the ascospore wall and extended over the mid-septum, unravelling immediately in sea water to form a long thin filament. Asexual morph Undetermined.

Material examined: TAIWAN, Nankunshen, on a dead stem of Phragmites australis (Cav.) Trin. ex Steud. (Poaceae), 22 November 2010, Ka-Lai Pang, F27870 (holotype, National Museum of Natural Science, Taiwan); ex-type living culture, BCRC FU 30316. GenBank LSU: KM624522; SSU: KM624521.

Notes: Natantispora unipolaris forms in a monophyletic clade with N. retorquens in the Halosphaeriaceae (Microascales, Ascomycota) with high bootstrap support(Fig. 1). Natantispora unipolaris is morphologically very similar to the type species N. retorquens, including globose tosubglobose ascomata, presence of catenophyses, hyaline, elongate-ellipsoidal ascospores with one septum, a polar appendage pad extending over the mid-septum which unfurls to form a long thread (Shearer and Crane 1980). Natantispora unipolaris differs in having only one ascospore appendage instead of two in N. retorquens; ascomata are smaller with many small oil globules and one large one in each cell. Tirispora unicaudata also has a single polar hamate appendage visible when mounted in sea water, but phylogenetically it is distant from N. unipolaris.

Fig. 1 Phylogram generated from Maximum likelihood (RAxML) analysis based on combined SSU and LSU sequence data of the Halosphaeriaceae. Maximum Likelihood bootstrap support values greater than 50 % are indicated above or below the nodes, the branches with Bayesian posterior probabilities greater than 0.95 are given in bold. The ex-types (reference strains) are in bold, the new isolates are in blue. The tree is rooted with Microascus trigonosporus AFTOL-ID 914 and Petriella setifera AFTOL-ID 956.

Fig. 2 Natantispora unipolaris (holotype). a Immersed ascoma with neck protruding to the surface b One-layered peridium of elongated cells with large lumina c Asci at various stages of development d–f Ascospores with an unfurling appendage at one end. Scale bars: a=30 μm, b–f=10 μm.