This is closely related to retroflexus and hybridus (with possible hybrids) and has probably been overlooked in eastern states, where it is adventive from southwestern states and Mexico (FNA 4; W). A. powellii differs from hybridus in its longer bracts (4-7 mm versus 2-4 mm), which are 2-3 times as long as sepals (versus 1-2 times); inflorescence usually stiff with erect branches (versus usually soft and lax with spreading branches); 2n = 34 (versus 32). For Ky. the only record is a coll. from "banks of Mississippi west of Henley Road" in HICK (MUR, GA; Grubbs 1989). A. powellii may also hybridize with more dioecious taxa in subgenus Acnida (FNA 4).