Ascocarps intraepidermal. In vertical section upper stromatal layer 15-30 µm wide, comprising brown to dark brown, angular cells, 5-8 .µm diam. A few cylindric, hyaline, periphysis-like cells, 10-15 x 2-3 µm, near opening. Lower stromatal layer 20-30 µm wide, of 3-5 layers of dark brown, thick walled cells 5-8 µm diam. A 15-20 µm wide layer of gelatinised tissue present between the lower stromatal wall and the sub-hymenium, extending a short distance up the sides of the hymenium, giving rise to few, branching, excipular-like elements.

Paraphyses 1.5-2 µm diam., swollen to 4-6 µm at the clavate apices, extending 10- 15 µm beyond asci. Asci 101-118 x 7.5-9 µm, subclavate, tapering in to a broadly truncate apex, wall uniform in thickness, non-amyloid, 8-spored. Ascospores 35-43.5 x 2-3 µm, clavate, tapering to the base, 0(-1) septate, hyaline, with a gelatinous cap.

ETYMOLOGY: clavatus = clavate; refers to ascospore shape.

C. clavatus is similar to C. phyllocladi, also found on Phyllocladus. The two species are indistinguishable macroscopically, and are similar in appearance in cross-section, both having a characteristic, gelatinous layer between the lower stromatal wall and the sub-hymenium. They differ in the size and shape of the asci and ascospores.

No rhytismataceous species have previously been reported on Phyllocladaceae. Two Hypoderma-like species have also been found on this host in New Zealand.