Collariella bostrychodes is a fungal decomposer of lignin and carbohydrate in the family Chaetomiaceae commonly found in soil and dung. The fungus is distinguished by a darkened collar-like ostiole around the ostiolar pore, giving the fungus its name. The fungus is highly variable in shape and form, giving raise to the belief that there are two subclades in the species. The ascospores range from lemon-shaped to nearly spherical with slightly pointed ends. It can grow to be pale green and later turn pale bluish grey or olivaceous with age. The fungus produces the toxic secondary metabolite, chaetochromin.
History and taxonomy
In 1877, the fungus was originally described by Friedrich Wilhelm Zopf in the Verhandlungen des Botanischen Vereins der Provinz Brandenburg for the Botanischer Verein der Provinz Brandenburg. He described the fungus as part of the genus Chaetomium and initially being named as Chaetomium bostrychodes. C. bostrychodes was originally described to have ellipsoid ascomata by Pier Andrea Saccardo in 1882, but later in 1963, Ames re-examined and described the species to have subglobose to ovoid ascomata instead. The fungus was noted as being unable to produce functional antheridia, which suggested it wasn't part of the heterothallic species of Chaetomium. The fungus was described as unique in the genus Chaetomium for possessing banded spores that are characteristic of no species of Chaetomium described in 1937.
The fungus was believed to have two subclades designated C. bostrychodes and C. bostrychodes (A), which were considered to be macroscopically indistinguishable but closely related enough to each other that both subclades were kept as the same species. The two subclades were previously suggested both to be either aberrant physiological or nearly related forms. Using phylogenetic analyses, combined with morphological comparisons to related genera and species, Wang and Samson determined C. bostrychodes to have morphological diversity specific to indoor Chaetomiaceae that required creating a new genus. The genus, Collariella, was created to include for this diversity, its name refers to the dark collar-like apex that occurs around the ostiolar pore of the ascomata. C. bostrychodes was then transferred to the new genus and renamed Collariella bostrychodes, with the two subclades then grouped together and placed under this name.
Morphology and phylogeny
Colonies of C. bostrychodes can grow 2.5 to 3.5 mm daily, usually without developing aerial mycelium. It can sometimes grow with pale green exudates and a green or uncoloured reverse. When young, C. bostrychodes appears as colourless and dextrinoid, but upon maturity, turns pale bluish grey or olivaceous with an apical germ pore . C. bostrychodes often are darkened around the 25 to 35 μm wide ostiolar pore, giving the genus its name of Collariella. Chaetomium convolutum can have a disposition to develop into some forms of C. bostrychodes, developing narrowly ellipsoidal or narrowly ovoidal perithecia restricted just below the darkened periostiolar collar. Similarly, C. bostrychodes appears similar morphologically to Collariella hilkhuijsenii, but C. bostrychodes can be distinguished via their larger ascospores and thicker terminal ascomatal hairs compared to those of C. hilkhuijsenii. The ascomatal walls are brown or ochraceous and composed of angular 5 to 12 μm cells. These tend to fracture underneath the terminal hairs, which then break away as a unit. Brown ascomatal hairs grow mainly from the apical disc, usually appearing as helically coiled in the apical region with little branching. The hairs are either verrucose or warty, which are about 4.5 to 6.5 μm thick with occasionally coiled branches. Lateral seta-like hairs are often also present and have tapered or clavate terminal ends with septate. These hairs break away at maturity with no aerial mycelium. C. bostrychodes develops perithecia late and possesses tightly coiled black terminal setae. The terminal hairs are branched, forming one spiral on another. The ascospores are considerably larger on average than those of C. robustum.