On living leaves of Gahnia setifolia (A. Rich.) Hook. f. Auckland, Auckland Domain, 25.VII.1978, W.S.M. Versluys & P.R. Johnston (PDD 38462); Auckland Domain, 28.IX.1978, W.S.M. Versluys & E.H.C. McKenzie (PDD 38658) [Holotype]; same details (PDD 38656); Auckland Domain, 12.X.1978, E.H.C. McKenzie (PDD 40910); Northcote, Kauri Glen Park, June 1978, W.S.M. Versluys (PDD 38657).

Colonies on the adaxial leaf surface. Mycelium mostly superficial, pale straw coloured, branched, minutely verruculose, septate, 1.5-2.5 µm thick. Stroma absent. Conidiophores originating from brown, smooth, sometimes swollen cells 10-30 µm wide, macronematous, mononematous, mostly single, usually unbranched, erect, straight or flexuous, occasionally with 1 or 2 geniculations, smooth, septate, brown, paler towards the apex, up to 150 µm long x 3-4.5 µm thick. Conidiogenous cells polyblastic, integrated, terminal becoming intercalary, sympodial, conidial scars thickened and slightly prominent 2-3 µm wide. Conidia solitary, substraight, cylindrical or narrowly obclavate, apex rounded, base obconically truncate, straw coloured, minutely verruculose, indistinctly septate with up to 30 septa, 20-300 µm long x 3-5 µm wide in the broadest part; hilum 2-3 µm thick.

Coloniae adaxiales. Mycelium ex hyphis plerumque superficialibus, stramineis, ramosis, minute verruculosis, septatis, 1.5-2.5 µm crassis. Stroma nullum. Condiophora e cellulis fuscis, laevibus, basi interdum ad 10-30 µm inflata, macronematosa, mononematosa, plerumque singula, saepe eramosa, erecta, recta vel flexuosa, interdum apice geniculata, laevia, septata, brunnea, apicem versus pallidiora, usque ad 150 µm longa x 3-4.5 µm crassa. Cellulae conidiogenae polyblasticae, in conidiophoris incorporatae, terminales et intercalares, sympodiales, cicatrices conidiales 2-3 µm latae. Conidia solitaria, subrecta, cylindrica vel obclavato-cylindrica, straminea, minute verruculosa, usque ad 30 indistincte septata, 200-300 µm longa x 3-5 µm lata, cellula apicali rotundata, cellula basali truncata; hilo 2-3 µm lato. In foliis cyperaceae speciei Gahnia setifolia (A. Rich.) Hook. f. Holotypus PDD 38658.

Stenella gahniae is associated with a leaf spot of Gahnia setifolia. Leaf spots (Fig. 5) are at first an indefinite yellow-orange discolouration, sometimes with a minute reddish-brown centre. Later, a general yellow-orange discolouration containing many minute reddish-brown areas develops, giving the leaf a rusted appearance. Discoloured areas sometimes cover the width of the leaf, and can be up to approx. 40 mm long. Discolouration is most distinct on the abaxial leaf surface.
The genus Stenella was erected by Sydow (1930). The type species, S. araguata H. Syd. was redescribed and illustrated by Ellis (1971), and most of the known species were figured and redescribed by Ellis (1976). Stenella species are usually associated with indistinct leaf blotches on dicotyledonous hosts; only S. caryotae Liu & Liao on the palm, Caryota mitis Lour., has been recorded on a monocotyledon. An interesting feature of Stenella is the verruculose hyphae, growing externally on leaves. The genus is also distinguished by the usually rough-walled, normally catenulate, 'Cercospora- like' conidia, and the thickened but flat conidial scars.