Stigmidium


Stigmidium is a genus of lichenicolous fungi in the family Mycosphaerellaceae.

Taxonomy

The genus was circumscribed by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon in 1860, with Stigmidium schaereri assigned as the type species.

Description

Stigmidium species are minute, mostly lichen-dwelling fungi that usually lack a visible body. Most live embedded in the tissues of their host lichens, though one species appears genuinely lichenised and a few are parasites of brown algae. Their vegetative filaments are branched, pale to light brown, and consist of elongate cells that are mostly within the host; compact tissue masses are not formed.
The ascospore-producing structures are tiny, dark, flask-shaped perithecia with short necks and thick, melanised walls. They develop within the host thallus and may later break through the surface. Stiff hairs are absent, but some species show small hyphal outgrowths or grow within a mat of surface mycelium. Inside the perithecium, the sterile tissue is variable and made up of narrow that are often poorly developed and frequently break down as the spores mature; in some species, the pore is lined by short filaments called.
The spore sacs are few in number, club- to sack-shaped, thick-walled, and . They lack a differentiated tip structure, do not stain blue in iodine, and usually contain eight ascospores. The spores are arranged in two rows, cylindrical to club-shaped or ellipsoidal, thin- and smooth-walled, usually colourless but sometimes browning late in development. They are typically 1-septate, and each cell often contains two oil droplets, which can give the illusion of additional cross-walls; no outer gelatinous coat is present. Asexual states are unknown for most species, and no secondary metabolites have been reported.

Species