Ascomata subcuticular. In vertical section upper wall of unopened ascomata up to 50-80 µm thick, comprising mostly brown to dark brown, thick-walled, angular cells, but near middle of the ascomata, along the future line of opening, the inside part of the wall comprises thinner-walled, paler cells. Wall starts to split open from outside edge, and as the split forms, hyaline, cylindric cells start to develop along the exposed face of the broken wall. In some hosts the split in the ascomatal wall may begin to develop prior to the covering host cuticle breaking. In opened ascomata the upper wall is 60-110 µm thick near the ascomatal opening, then becoming either abruptly, or gradually, thinner toward the outer edge, where it is 10-25 µm thick. Upper wall comprising dark brown, thick-walled, angular, 4-8 µm diam. cells. Exposed face of the broken upper wall is lined with cylindric, hyaline, thin-walled, 20-30 x 3-4 µm cells. Lower wall 10-15 µm thick, of 2-4 layers of dark brown, thick-walled, angular to globose,4-6 µm diam. cells.

Paraphyses 1.0-1.5 µm diam., circinate at apex, extending 5-15 µm beyond asci. Asci 110-160 x 11-14 µm, clavate-stipitate, tapering to small, truncate apex, wall often with small pore at apex, 8-spored, spores confined to upper half of ascus. Ascospores 15-28 x 2.5-5.5 µm (see notes below), in face view more or less naviculate in shape, widest point near centre, tapering slightly to rounded apex, and more sharply to acute base. In side view spores slightly curved. Spores surrounded by well-developed gelatinous sheath. Conidiomata subcuticular. In vertical section more or less globose in shape, upper wall 5 µm thick, comprising dark material with no obvious cellular structure, lower wall of 2-3 layers of dark brown, thick-walled, angular cells on which the conidiogenous layer develops. Conidiogenous cells 7-12 x 2-4.5 µm, tapering to apex, proliferating either sympodially, or rarely percurrently. Conidia 3-5 x 1-1.5 µm, cylindric, ends rounded, hyaline, 0-septate.

CHARACTERISTICS IN CULTURE: Spores germinated on agar plates within 24 hours. Cultures on OA 85 mm diam. after 6 weeks, aerial mycelium white to grey, sparse, agar surface pinkish to vinaceous brown, with scattered globose, black-walled conidiomata. Conidiomata splitting to expose grey conidial ooze. Conidiogenous cells and conidia as described from plant material.

Despite small differences, there is a strong overall similarity between the New Zealand collections and recent descriptions of H. rubi by Cannon & Minter (1986) and Powell (1974). The New Zealand collections show a wide range of ascospore length and width (15-28 x 2.5-5.5 µm), and also considerable variation between collections in average spore length and width. This variation correlates to some degree with host substrate. Ascospores taken from seven collections on Rubus spp. (both native and introduced) had a range of spore lengths confined to the upper end of the range for H. rubi as a whole, and spore widths confined to the lower end of the range of variation, with an average spore size of 24.1 x 3.3 µm. Spores from collections from native hosts, such as Pseudopanax spp. (16 collections, average spore size 19.6 x 3.9 µm), Griselinia spp. (6 collections, average spore size 19.5 x 3.8 µm), Olearia spp. (6 collections, average spore size 19.0 x 3.8 µm), and Coprosma spp. (6 collections, average spore size 19.4 x 4.3 µm), had spore lengths confined to the lower end of the range for H. rubi as a whole, and spore widths confined to the upper end of the range. Although there is overlap between the range of spore sizes from Rubus versus those from other hosts, both the ranges and the averages do differ. In all other characteristics of both teleomorph and anamorph the two groups cannot be distinguished. They are not recognized here as taxonomically distinct, however the differences in ascospore size may indicate that they represent genetically isolated populations.

Two distinct species, H. cordylines and H. dundasicum, very similar to H. rubi, have been recognised from New Zealand, primarily on the basis of ascospore shape and host preference. All the collections recognised here as belonging in H. rubi have more or less naviculate ascospores. The spores are widest near the centre, taper slightly to the rounded apex, and more markedly to the acute base. The ascospores of H. dundasicum are slightly narrower than those of H. rubi, are cylindric in shape, and although acute to the base, taper from only very close to the base itself. This character, which correlates with asci slightly narrower (8-11 µm wide) than those of H. rubi, has been seen in all collections on Ericaceae from New Zealand.

H. cordylines can be distinguished from H. rubi by ascospore shape, having elliptic or oblong-elliptic spores which are uniform in shape to both ends of the spore, and in having longer anamorph conidia. These characters have been seen in all collections examined from Cordyline and Phormium.

Fig. 10 A-F and Fig. 11 A show stages in ascomatal development of H. rubi. A similar pattern of development is found in all the Hypoderma spp. included in this paper. When first visible the developing ascomata comprise a lenticular shaped group of hyaline, plectenchymatous cells beneath which is the lower wall layer, comprising a single row of brown, thick-walled cells (Fig. 10 A). The lower wall under-goes more or less no change during subsequent stages of ascomatal development. At about the same time as the upper wall of the ascomata develops, a cavity forms within the hyaline plectenchyma, and paraphysis-like elements extend up into this cavity (Fig. 10 B, C). As the ascomata develop they increase in size, the upper wall becomes thicker toward the centre of the ascomata, the wall becomes internally differentiated, the paraphyses become longer, and asci begin to develop (Fig. 10 B, C, D). The upper wall comprises mostly brown, thick-walled, angular cells, but near the centre of the ascomata, in the inner half of the wall, is a wedge-shaped group of pale, thin-walled cells, and lining the inner edge of the wall is a layer of hyaline, short-cylindric, periphysoid-like cells (Fig. 10 D, E). The ascomatal upper wall starts to split open from the outside, and at the same time as the split develops, hyaline, thin-walled, cylindric cells form along the exposed face of the broken wall (Fig. 10 F), and in opened ascomata form a well-developed, persistent layer (Fig. 11 A). The periphysoid-like cells evident in immature ascomata are not visible in opened ascomata, presumably crushed by pressure exerted by the developing hymenium.