Cladosporium Link, Mag. Gesell. naturf. Freunde, Berlin 7: 37 (1816) .
In vivo: Dematiaceous hyphomycetes; anamorphs of Davidiella. Colonies punctiform to effuse, mostly olivaceous-brown to blackish brown or with a grey-olivaceous appearance, velvety, floccose or villose. Mycelium internal or external, superficial; hyphae branched, septate, subhyaline to usually pigmented, smooth, sometimes slightly rough-walled to verruculose. Stromata absent to sometimes well-developed. Conidiophores mononematous, usually macronematous, solitary, fasciculate, in small to large fascicles, loosely to densely caespitose, usually erect, occasionally subdecumbent, decumbent or repent, straight to flexuous, unbranched or branched, continuous to septate, subhyaline to usually distinctly pigmented, smooth to verruculose, proliferation holoblastic, occasionally enteroblastic (after a period when growth has stopped and then resumed), usually sympodial, rarely monopodial (sometimes leaving coarse annellations from repeated enteroblastic proliferation). Conidiogenous cells integrated, terminal or intercalary, monoblastic or usually polyblastic, mostly sympodially proliferating, more or less cylindrical, geniculate-sinuous or nodulose, sometimes with unilateral swellings, conidiogenous loci usually conspicuous, protuberant, composed of a central convex dome surrounded by a more or less raised periclinal rim (coronate), thickened, refractive or barely to distinctly darkened; conidial formation holoblastic. Conidia solitary or catenate, in unbranched or branched acropetal chains, amero- to phragmosporous, shape and septation variable, usually subglobose, ovoid, obovoid, ellipsoid, fusiform, limoniform to cylindrical, aseptate or with several transverse eusepta, rarely with a single longitudinal septum, subhyaline to usually pigmented, smooth, verruculose, verrucose, echinulate, cristate, hila protuberant, coronate, with a central convex dome and raised periclinal rim, thickened, refractive to darkened; microcyclic conidiogenesis often occurring. In vitro: Stromata usually lacking. Conidiophores usually solitary, arising terminally or laterally from plagiotropous or ascending hyphae, often longer than in vivo. Micronematous conidiophores, lacking in vivo, are often formed in culture. Conidial chains often longer than in vivo (species with solitary conidia are often capable of forming conidial chains in culture) (Adapted from Bensch et al. 2012).
Type species: Cladosporium herbarum (Pers.) Link.
Notes: Cladosporium was introduced by Link (1815) with C. herbarum as type species. Cladosporium is a ubiquitous genus in the family Cladosporiaceae of the recently proposed order Cladosporiales (Abdollahzadeh et al. 2020). Cladosporium is morphologically characterized by its asexual morph, which shows discerned conidiophores producing acropetal chains of conidia from mono- or polyblastic conidiogenous cells. The conidiogenous cells and conidia display conidiogenous loci (scars) with a unique coronate feature comprising a central convex dome enclosed by a raised periclinal rim, typically thickened, refractive and darkly pigmented (David 1997). Cladosporium share similarities to genera such as Hyalodendriella, Ochrocladosporium, Rachicladosporium, Rhizocladosporium, Toxicocladosporium, Verrucocladosporium and Neocladosporium (Crous et al. 2007; Bezerra et al. 2017). Cladosporium can be distinguished from similar genera based on DNA sequence data. Several studies provided multi-gene analyses of Cladosporium and more than 230 species have been recognized in the Cladosporium complex. Species in the Cladosporium s. str. is well-delineated using the sequences of the internal transcribed spacers (ITS) of the rDNA and of the two protein encoding genes, translation elongation factor 1-α (tef1) and actin (act). Cladosporium was formerly heterogeneous and comprised 772 names (Dugan et al. 2004). Heuchert et al. (2005) studied Cladosporium spp. residing on other fungi, and Schubert (2005) provided a detailed account of foliicolous species. A reexamination and new circumscription of Cladosporium s. str. was given by Crous et al. (2007a). The most significant morphological characters of Cladosporium are the shape, thickness and density of conidiophores, the presence of ramoconidia, and the formation and ornamentation of conidia. Bensch et al. (2012) provided a detailed explanation of Cladosporium. Species within Cladosporium are splitted into three species complexes based on morphology and phylogeny, i.e., the Cladosporium cladosporioides, Cladosporium herbarum and Cladosporium sphaerospermum complex (Bensch et al. 2012; Marin-Felix et al. 2017). The Cl. cladosporioides species complex is characterized by narrowly cylindrical or cylindrical-oblong, non-nodulose, typically non-geniculate conidiophores and conidia with a rather inconstant surface ornamentation ranging from smooth to erratically verrucose-rugose or rough-walled. the Cl. herbarum species complex is differentiated by nodulose conidiophores, with conidiogenesis limited to swellings, and verruculose, verrucose or echinulate conidia; and the Cl. sphaerospermum complex is identified by the formation of several globose or subglobose terminal and intercalary conidia with inconstant surface ornamentation and seldom poorly discerned conidiophores (Bensch et al. 2012, 2015). Schubert et al. (2007) studied the biodiversity in the Cladosporium herbarum complex and suggested standardization of methods for Cladosporium taxonomy and diagnostics.