Aspergillus spp. grow rapidly on most culture media. Microscopically, all cultured Aspergillus spp. produce a swollen vesicle ("aspergillum") at the end of each conidiophore (which is a feature distinct to the genus). Identification to the species level is based on characteristic colony and microscopic morphologies.
A. fumigatus colonies are blue-green with a distinct white apron and a light-colored or white reverse. Microscopically, the conidiophores terminate in a swollen vesicle with a single row of phialides (uniseriate) that cover only the top 2/3 of the vesicle. Each phialide gives rise to a chain of small (2-4 µm) round conidia.
A. flavus produces yellow-green to olive colonies with a light-colored reverse. Circumferential phialides are seen microscopically. Some strains are uniseriate while others are biseriate. The conidiophores of A. flavus are also often times spiny or rough.
The image to the top right is Aspergillus fumigatus demonstrating filamentous conidiophore, which terminates in a bulbous, spheroid vesicle. Atop the distal two-thirds of this vesicle, a uniseriate, i.e., single row, of phialides sprout, each of which anchors its respective chain of spherical conidiospores. The bottom right picture is A. flavus demonstrating a biseriate conidial configuration.
Images courtesy of the CDC.
https://phil.cdc.gov/Details.aspx?pid=4298
