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Square-stemmed monkeyflower flowers arise singly from the upper leaf axils; they are tubular and ~1" long. The calyx is light green, elongate (about 2/3" — quite large relative to the corolla), and tubular, with five sharp longitudinal ridges/wings that project into lance-like teeth; the flower pedicels are hairless and at least as long as the calyx. The corolla is usually pale blue-violet (rarely pink or white) with a two-lobed, erect upper lip (folded so the upper sides of the lobes are back to back) and a three-lobed lower lip with a patch of yellow on either side of the midline. The throat is lined with hairs and obscured by ridges in the lower lip. The seed capsules develop within the persistant calyx. The flower is quite prolific, producing 500-1000 seeds per flower. Four stamens and a single pistil are present but not visible externally. Square-stemmed monkeyflower strongly prefers moist or wet areas. The only other Illinois monkeyflower (winged monkeyflower, Mimulus alatus) apparently does not occur this far north.

Mimulus

Mimulus ringens

square-stemmed monkeyflower [Blooms: Jul-Sep]