Ascocarps scattered to clustered, immersed, globose to subglobose and laterally compressed between vascular strands of host, 190-330 µm long and 200 µm high, non-papillate. Ascocarp in section broadly elliptic to depressed ovate; ascocarp wall 10-20 µm and 3-5 cells wide, textura prismatica; cell walls evenly thickened and pigmented, but slightly thicker and more heavily pigmented surrounding the ostiole; cells 5-11.5 x 4.5-6.5 µm. Asci numerous, bitunicate, narrowly obovate, short stalked, 8-spored, 75.5-108.5 x 15-17.5 µm. Ascospores irregularly tristichous, narrowly elliptical, 3-septate, constricted at all septa, second cell slightly swollen, (note: old ascospores elliptic oblong, and all cells slightly swollen), straight to slightly curved, punctate, luteous, at first guttulate, later non-guttulate, 29-33.5 x 5-7 µm; gelatinous sheath entire, broadest at the second cell. Physes numerous, septate, sparsely branched, hyaline, 2-3 µm wide. Hyphae darkening epidermis surrounding ostiole.

Ascocarpia sparsa ad gregaria, iminersa, globosa ad subglobosa, a latere compressa, 190-330 µm lata, 200 µm alta, non-papillata, muri 10-20 µm crassi. Asci numerosi, bitunicati, anguste obovati, breviter stipitati, octospori, 75.5-108.5 x 15-17.5 µm. Ascosporae irregulariter tristichae, anguste ellipticae, triseptatae, in septis omnibus constrictae, rectae vel leniter curvatae, punctatae, luteae, primo guttulatae, postea non-guttulatae, 29-33.5 x 5-7 µm; loculus secundus leniter inflatus; vagina gelatinosa continua praeditae. Physes numerosae, septatae, tenuiter ramosae, 2-3 µm crassae.
Holotypus: PDD50249 ex Scirpus nodosus Rottb.

Only three species of Phaeosphaeria are recorded on Scirpus, these are P. eustoma on S. holoscheonus from Italy, P. caricus on S. silvaticus from Switzerland (Leuchtmann 1984), and P. papua-alpina on Scirpus sp. from Papua New Guinea (Kobayasi & Otani 1971). P. kukutae is easily distinguished from these by its three-septate, fusiform, punctate ascospores.
Etymology: kukuta, Maori for Scirpus.

Specimens examined, New Zealand: on Scirpus nodosus Rottb., east of Sinclair Head, Wellington south coast, 17 June 1984, G. S. Ridley, PDD50248; and 22 September 1985, PDD50249 Holotype.