Ascomata subcuticular. In vertical section the ascomatal initial comprises a lens-shaped group of hyaline, plectenchymatous cells oriented more or less parallel to the surface of the host leaf, with darkened, angular cells developing toward the lower surface of the plectenchyma. As the ascomata develop, and paraphyses start to differentiate, darkened angular cells begin to develop along the upper as well as the lower edge of the ascomata. As the paraphyses elongate and asci begin to develop the upper wall of the ascomata becomes up to 60 µm thick near the centre of the ascomata, narrower toward the edges. The upper wall comprises mostly brown to dark brown, thick-walled, angular cells, but near the centre of the ascomata, along the future line of opening, toward the inside of the wall, is a group of hyaline thin-walled, angular cells. The inside of the wall is lined with a poorly developed layer of hyaline, thin-walled, short-cylindric, downward-oriented cells. In some ascomata the upper wall retains this appearance until opening, but in others, at about the stage when ascospores are first starting to differentiate, the cells along the lower part of the pale area along the future line of opening become darkened and thick-walled. At about the same stage of development, some ascomata develop an extra layer up to 20 µm thick, of hyaline, thin-walled, vertically oriented cells between the upper wall and the host cuticle. The upper wall starts to split open from the outside, and as the wall splits a layer of thin-walled, hyaline, cylindric cells develops along the exposed face of the broken wall. In opened ascomata the upper wall is up to 100 µm thick near the opening, becoming narrower toward the edge of the ascomata, and comprises brown to dark brown, thick-walled, angular cells. The exposed face of the broken upper wall is lined with a palisade-like layer of thin-walled, 10-15 x 1-2 µm, cylindric cells. The layer between the upper wall and the cuticle present in some ascomata is retained after the ascomata open. In opened ascomata the lower wall is 5-10 µm thick, comprising 1-3 layers of brown to dark brown, angular to cylindric cells.

Paraphyses 1.5-2.5 µm diam., undifferentiated at apex, extending 15-25 µm beyond asci. Asci 130-200 x 18-22 µm, clavate to subsaccate, tapering to truncate apex, wall more or less undifferentiated at apex, 8-spored, development of asci sequential. Ascospores 40-70 x 5.5-8 µm, bifusiform, 1.5-2.5 µm wide at constriction, 0-1 septate, surrounded by a 2-4 µm thick gelatinous sheath. Conidiomata 0.2-0.3 mm diam., round in outline, pale brown, with a darker line around the outside edge, subcuticular. In vertical section the upper wall is more or less absent. Lower wall 5-10 µm thick, comprising 2-3 layers of brown to dark brown, thick-walled, angular cells. Conidiogenous cells develop on the lower wall, 6-10 x 2-3 µm, solitary, cylindric, with percurrent proliferation, wall of the conidiogenous cell thickened and often slightly flaring at the single, apical conidiogenous locus. Amongst the conidiogenous cells, near the centre of ascomata, are narrow-cylindric, hyaline, sterile elements extending almost to the top of the conidiomata. Conidia 4-6 x 1 µm, cylindric, ends rounded, nonseptate, hyaline.

CHARACTERISTICS IN CULTURE: Ascospores germinated from PDD 43973 and 57549 on agar plates, on oatmeal agar colonies 20-30 mm diam. after 5 weeks, surface of colony undulate, pale brown, aerial mycelium low, felted, white, or lacking, pale brown in reverse.

ETYMOLOGY: refers to the liliaceous host substrate.

NOTES: This is the only species of Rhytismataceae known from Collospermum, but Coccomyces limitatus, Lophodermium asteliae, and L. minus are known also from Astelia. Hypoderma liliensis is easily distinguished from these other species by the bluish differentiated zone along the edge of the ascomatal opening, and microscopically by the large, subsaccate asci, and bifusiform ascospores.

Although the ascus shape, and ascus and ascospore size, are unusual for Hypoderma, H. liliensis possesses all the characters used by Johnston (1990) to redefine this genus. Also atypical of Hypoderma is the darkening of the inner edge of the upper wall seen in some collections of this species, but as this feature is not found consistently in all collections, it is not considered of generic significance. The development of a layer of hyaline, cylindric cells between the upper wall and the cuticle is also unusual. However, a similar phenomenon has been seen in a few collections of Hypoderma rubi (Persoon:Fries) de Candolle ex Chevallier from New Zealand, although the layer of cells in this case is not as well developed as in H. liliensis, and it forms later in the development of the ascomata, appearing only shortly before the ascomata open.

The size and shape of the asci and ascospores of H. liliensis are similar to those of Duplicaria empetri (Persoon:Fries) Fuckel and many of the conifer-inhabiting species of Rhytismataceae. Duplicaria differs in having circular ascomata with radiate opening splits, and an upper wall with no internal differentiation in unopened ascomata, barely thickened toward the opening, and with no cylindric, thin-walled cells lining the exposed face of the broken upper wall in opened ascomata. The conifer-inhabiting species with similar ascospores and asci differ in having ascomata which develop subepidermally, which lack a darkened lower wall, and lack differentiated cells along the edge of the opening split. The one conifer-inhabiting genus with large, bifusiform ascospores and subcuticular ascomata, Bifusella, has synchronous development of the asci, and lacks persistent paraphyses.