Acanthaceae, the Acanthus Family
Herbs with opposite simple leaves; corolla of united petals, 2-lipped or almost regular; stamens 2 or 4, attached to the corolla; ovary 2-celled.
| 1a. Corolla about 10 mm. long; flowers in dense heads (4-10 dm. high; flowers blue or white, summer) | Water Willow, Dianthera americana. |
| 1b. Corolla about 30 mm. long; flowers axillary (3-8 dm. high; flowers blue, in summer) (Ruellia) — 2. | |
| 2a. Foliage glabrous or slightly pubescent | Ruellia, Ruellia strepens. |
| 2b. Foliage densely hirsute | Ruellia, Ruellia ciliosa. |