| Stigmidium | |
|---|---|
 | |
| Herbarium specimen of Stigmidium marinum, preserved by Richard Deakin in 1854 | |
Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Dothideomycetes |
| Order: | Capnodiales |
| Family: | Mycosphaerellaceae |
| Genus: | Stigmidium Trevis. (1860) |
| Type species | |
| Stigmidium schaereri (A.Massal.) Trevis. (1860) | |
| Species | |
See text | |
| Synonyms [1] | |
| |
Stigmidium is a genus of lichenicolous (lichen-dwelling) fungi in the family Mycosphaerellaceae. [2]
The genus was circumscribed by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon in 1860, with Stigmidium schaereri assigned as the type species. [3]
Stigmidium species are minute, mostly lichen-dwelling fungi that usually lack a visible body (thallus). Most live embedded in the tissues of their host lichens, though one species appears genuinely lichenised (forming a partnership with green algae of the genus Dilabifilum ) and a few are parasites of brown algae. Their vegetative filaments (hyphae) are branched, pale to light brown, and consist of elongate cells that are mostly immersed within the host; compact tissue masses ( stromata ) 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 ( erumpent ). Stiff hairs ( setae ) are absent, but some species show small hyphal outgrowths or grow within a mat of surface mycelium. Inside the perithecium, the sterile tissue (the hamathecium ) is variable and made up of narrow pseudoparaphyses that are often poorly developed and frequently break down as the spores mature; in some species, the pore (ostiole) is lined by short filaments called periphysoids . [4]
The spore sacs (asci) are few in number, club- to sack-shaped, thick-walled, and fissitunicate (the wall splits into layers to release the spores). 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 (rarely with three septa), and each cell often contains two oil droplets ( guttules ), which can give the illusion of additional cross-walls; no outer gelatinous coat ( perispore ) is present. Asexual states (anamorphs) are unknown for most species, and no secondary metabolites (lichen products) have been reported. [4]
