Flag leaf blades 8-22 cm long. Panicles 9-17 cm long. Glumes8-11.5 mm long;lemmas 8-10 mm long; anthers 3-4 mm long. 2n = unknown.
Ammophila breviligulata subsp. champlainensis differs from Ammophila breviligulata subsp. breviligulata primaruly in its earlier anthesis, from June to early July rather than late July to September. It also tends to be smaller but the two overlap in all their morphological characteristics.