Cladosterigma
Cladosterigma is a fungal genus in the family Gomphillaceae. It is monospecific, comprising the single species Cladosterigma clavariella. The fungus is a hyperparasite: it grows on living leaves of myrtle relatives where it parasitises a plant-pathogenic fungus in the genus Phyllachora. It is known only from an asexual state that forms conspicuous, yellow, branched synnemata erupting through the leaf surface.
Taxonomy
The genus Cladosterigma was established by Narcisse Théophile Patouillard in 1892 with C. fusisporum from Ecuador; Carlo Luigi Spegazzini had earlier described Microcera clavariella from Paraguay on Eugenia leaves associated with Phyllachora. In 1919 Höhnel recombined Spegazzini's species as Cladosterigma clavariellum and treated it as the same species as Patouillard's taxon, leaving Cladosterigma with a single accepted species and C. fusisporum in synonymy.For more than a century Cladosterigma was variously regarded as a basidiomycete and placed among jelly fungi before later authors questioned that interpretation. Multi-locus DNA data finally resolved it as an ascomycete in the order Graphidales, where it represents an early-diverging lineage in a family otherwise dominated by lichen-forming fungi; within the order it is the first non-lichenicolous mycoparasitic member.
Description
Cladosterigma clavariellum is known only from an asexual morph. Colonies develop on the leaf surface of infected hosts and are most abundant on the underside of leaves. The fungus produces closely bunched-together synnemata that break through the epidermis. These structures are made of tightly packed conidiophores whose tips are covered by a continuous layer of conidiogenous cells.Conidiogenous cells are polyblastic. The conidia are narrowly ellipsoid to, 1–3-septate, and terminate in a distinctive "foot cell" reminiscent of some Fusarium species; the sexual morph is unknown.
Habitat and distribution
The species is a hyperparasite that invades the and fruiting bodies of Phyllachora on living leaves of Eugenia species, erupting through the plant epidermis to form synnemata. Material examined in the modern study comes from Minas Gerais, Brazil, while the historical types derive from Paraguay and Ecuador ; together these data indicate a Neotropical distribution.Within Graphidales, most genera are lichen-forming or lichenicolous; Cladosterigma is unusual in growing exclusively on Phyllachora rather than on lichens. It has so far been recorded on Eugenia hosts and has not been reported outside that ecological niche.