species infecting maize and other grass species in the Americas represents a complex of closely related species.

The genus contains numerous obligate fungal parasites that produce raised, melanized structures called stromata on their plant hosts referred to as tar spot. Members of this genus are known to infect many grass species but generally do not cause significant damage or defoliation, with the exception of . which has emerged as an important pathogen of maize throughout the Americas, but the origin of this pathogen remains unknown.

A quantitative assay for Amaranthus palmeri identification.

Background: Amaranthus palmeri recently has been brought into the Midwestern USA as a contaminant in Conservation Reserve Program seeding mixes. Rapid species screening is required to mitigate the risk of continued species movement.

Results: Markers were developed for A.