Spikelets of Agrostis capillaris are awnless and the callus is glabrous where as the spikelets of A. castellana are awned and have a hairy callus. Using spikelets primarily as a means of identification is inconclusive since field specimens of A. castellana often are found awnless as well. A. castellana is vigorously rhizomatous, has a longer ligule and has finer, rolled, grey-green leaves than A. capillaris. The most conclusive way to differentiate between the two species is to use vegetative characters. (Baston, 1998).
agróstide blanca (Spanish), agrostide blanche (French), agrostide géante (French), agróstide mayor (Spanish), black bent, black bent grass, bonnet grass, fiorin, Fioringras (German), pasto quila (Spanish), redtop, Riesenstraußgras (German), water bentgrass, weiße Straußgras (German)
Agrostis gigantea has short ligules, most noticeably on vegetative shoots. Near the base of the branches, A. gigantea has open panicles that lack spikelets (Manual, undated).
Agrostis sibrica has yellowish green spikelets and lanceolate leaves unlike A. capillaris (IPAO, undated).
Agrostis capillaris (colonial bentgrass) is easily confused with A. stolonifera (creeping bentgrass) and the two often form hybrids. Creeping bentgrass can be distinguished by its longer ligules and stolons (Garry Oak Ecosystems Recovery Team, 2003).