Argyrochosma fendleri is occasionally confused with A . limitanea , which can have slightly flexuous rachises and pinna costae. All A . limitanea specimens with slightly flexuous rachises and costae have 32 spores per sporangium, whereas specimens of A . fendleri consistently have 64. This southern Rocky Mountain species is the only member of the genus that is found on acidic substrates such as granite.