Ascocarps scattered to clustered, immersed, subglobose, c. 250 µm diam. and 60 µm high, ostiole with short papilla; ascocarp in section depressed ovate; ascocarp wall 10-20 µm and 7 cells wide, textura prismatica, cell wall thickening and pigmentation angular to more evenly distributed in cells surrounding the ostiole; cells of ascocarp base tending to textura angularis; cells 4-8 µm diam. Asci numerous, bitunicate, narrowly oblong elliptic, very short-stalked, 8-spored, 56-85 x 11-17.5 µm. Ascospores irregularly biseriate, narrowly elliptic, 3-septate, slightly constricted at the septa, straight to slightly curved, smooth, very pale luteous, guttulate, 22.5-29 x 4-5 µm; gelatinous sheath thin and entire. Physes numerous, septate, sparsely branched, 1-2 µm wide.

Ascocarpia sparsa ad gregaria, immersa, subglobosa, circa 250 µm in linea media et 60 µm alta, non ad breviter papillata, paries 10-20 µm crassa. Asci numerosi, bitunicati, anguste oblongi elliptici, breviter stipitati, octospori, 56-85 x 11-17.5 µm. Ascosporae irregulariter distichae, anguste ellipticae, triseptatae, rectae vel leniter curvatae, laeves, satis luteolae, guttulatae, 22.5-29 x 4-5 µm; ad septa leniter constricta; vagina gelatinosa tenuis, continua praeditae. Physes numerosae, septatae, tenuiter ramosae, 1-2 µm crassus.
Holotypus: PDD50261 ex ligno decorticato.

P. waikanaensis fits the generic concept with a typical Phaeosphaeria hamathecium of distinct and sparsely branching physes. It differs from other members of the genus in the darker brown thickening concentrated in the ostiole region of the ascocarp (Dr 0. Eriksson pers. comm.). P. waikanaensis is the only member of the genus to be found on wood rather than on the typical graminicolous or herbaceous substrates.
Etymology: Waikanae, Maori place name

Specimens examined. New Zealand: on decorticated wood collected at high tide mark, Waikanae River estuary, Waikanae, February 1982, G. S. Ridley, PDD50261 Holotype.