Melaspileella proximella

Melaspileella produces tiny, black fruiting bodies that appear as solitary, rounded stromatic ascomata on the surface of bark. The outer wall (peridium) of each ascoma consists of two layers: an external layer of thick-walled, black cells and an inner layer of lighter brown to nearly hyaline cells of a Latin type. Inside the ascomata, numerous filamentous pseudoparaphyses (sterile filaments) are present; they are hyaline and mostly unbranched, but have brownish pigmented tips around the asci. The asci are eight-spored, bitunicate (having a double wall), and broadly club-shaped (clavate) to almost spherical in shape, with a rounded apex and a short stalk (pedicel). Each ascus contains eight ascospores that are hyaline, one-septate (two-celled), with the upper cell slightly larger than the lower cell. A distinctive feature of the spores is that they bear 2–3 slender appendages (setulae) at the poles; these appendages are visible in fresh or wet spores but tend to disappear when the spore dries. No asexual reproductive stage is known for Melaspileella (the fungus is only known from its sexual morph).

Melaspileella proximella is a saprobic fungus that grows on the bark of living or dead woody plants. It does not form a lichen thallus (no photobiont is present), although it may superficially resemble a thin crust on bark (a "crustose, endophloedal" growth). This species has been recorded on the trunks and branches of a variety of trees and shrubs, including conifers like pine (Pinus) and juniper (Juniperus), as well as broad-leaved trees such as linden (Tilia). The species is interpreted as a saprobe of bark tissues rather than a pathogen of the host plant. In terms of distribution, Melaspileella proximella is known from temperate regions of the Northern Hemisphere. It has been documented in multiple parts of Europe (for example, Scandinavia and central Europe) and in eastern North America. Recent records also indicate its presence in Asia (e.g. Siberia, Russia), suggesting a broad boreal-temperate distribution across Eurasia and North America. However, it is generally considered a rarely encountered fungus, likely overlooked due to its minute size and inconspicuous appearance on bark.

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