Colpoma juniperi, Colpoma juniperi
Colonies: on both living and dead twigs and branches, visible as scattered or clustered ascomata. Zone lines absent.
Anamorph: not known.
Ascomata: 1–2 mm diam., in external appearance circular, elliptical or irregular, erumpent through the host epidermis which initially tends to remain in place, later opening by 1–3 transverse, radial or irregular splits in the covering layer which then folds back in humid conditions revealing the pale grey or fawn coloured hymenium. Upper wall 40–80 μm thick, composed of ± globose to angular cells 5–7 μm diam. with pigmented walls, thicker nearer the split, where there is a clearly-defined hyaline to pale brown interior layer several cells thick. Lip cells absent or poorly defined. Lower wall 10–40 μm thick, composed of rather poorly-defined cells, with a distinct excipular layer composed of cells forming a poorly-defined textura angularis to ca 70 μm deep, pigmented lower down and becoming colourless higher up. Subhymenium intergrading with, and scarcely distinguishable from the exciple. Interascal tissue of paraphyses, filiform, often branched, colourless, aseptate or septate, thin-walled, markedly curled or coiled (but not swollen) at the apex, longer than the asci, enveloped in a mucous sheath. Asci 75–120 × 7·5–9 μm, arising from croziers, maturing sequentially, clavate, with a rather pointed apex, uniformly thin-walled, not blueing in iodine, opening by a narrow apical hole, 8-spored. Ascospores arranged in a fascicle, sometimes helically curved towards the top, 40–50 × 1–2 μm, filiform, almost straight, hyaline, thin-walled, smooth, aseptate, enveloped in a mucous sheath about 1 μm thick which is
sometimes slightly thicker at the spore apex.
Not formally assessed, but possibly Vulnerable due to its localized distribution, largely confined to native Caledonian pine woodlands. A further concern is that its host is threatened in this region by the invasive species Phytophthora austrocedrae.
This species is easily distinguished from other fungi on Juniperus due to its large size, filiform ascospores and growth in bark.
Colpoma crispum is a rather similar species found in bark of Larix and Picea in GB&I. It is reputed to have slightly wider ascospores, a blueish rather than grey hymenium and inconspicuous lip cells, but the two taxa are probably part of a species complex and need molecular research to distinguish between them more effectively.
In GB&I, recorded from living bark and dead wood of Juniperus communis, as a saprobe and perhaps also a weak parasite that fruits on moribund tissues.
In GB&I, restricted to northern Scotland, recorded from East Sutherland, Easter Ness, South Aberdeenshire, West Sutherland and Wester Ness.