Aspergillus colonies are usually fast growing, white, yellow, yellow-brown, brown to black or shades of green, and they mostly consist of a dense felt of erect conidiophores. Conidiophores terminate in a vesicle covered with either a single palisade-like layer of phialides (uniseriate) or a layer of subtending cells (metulae) which bear small whorls of phialides (the so-called biseriate structure). The vesicle, phialides, metulae (if present) and conidia form the conidial head. Conidia are one-celled, smooth- or rough-walled, hyaline or pigmented and are basocatenate, forming long dry chains which may be divergent (radiate) or aggregated in compact columns (columnar). Some species may produce Hülle cells or sclerotia.
For identification, isolates are usually inoculated at three points on Czapek dox agar and potato dextrose agar and incubated at 25oC. Most species sporulate within 7 days. Descriptions are primarily based on colony pigmentation and morphology of the conidial head. Microscopic mounts are best made using a cellotape flag or slide culture preparation mounted in lactophenol cotton blue. A drop of alcohol is usually needed to detach the cellotape flag from the stick, and to act as a wetting agent.
Key Features: Hyaline hyphomycete showing distinctive conidial heads with flask-shaped phialides arranged in whorls on a vesicle.