Description: This native plant is a winter annual about ½1½' tall and unbranched. The central stem is pubescent or hairless. The opposite leaves are up to 2" long and ¾" across; they may be pubescent or hairless. The lower leaves are oval or orbicular with a few blunt teeth along their margins; they are smaller than the other leaves and have slender petioles. The middle leaves are the largest and most conspicuous; they are oval or broadly lanceolate, often with a few blunt teeth along their margins, and they clasp the stem. The uppermost leaves are usually lanceolate and smooth along their margins; they are often sessile.
The central stem terminates in a whorl of 4-6 flowers. Sometimes individual flowers develop from the axils of the upper leaves as well; these axillary flowers have slender pedicels. Each flower is up to ¾" across, consisting of a green calyx and a blue/white corolla. The calyx has 5 slender teeth; it is often pubescent. The short tubular corolla is divided into upper and lower lips. The upper lip is cleft into 2 lobes that are white, while the lower lip is cleft into 3 lobes. The 2 outer lobes of the lower lip are bright blue, while the middle lobe of the lower lip is folded into a keel and hidden from view. This middle lobe contains the stamens and style of the flower. The blooming period occurs from mid- to late spring and lasts about 3 weeks. Each flower is replaced by a globoid capsule that contains a few large seeds. The root system consists of a slender taproot. This plant spreads by reseeding itself; it often forms colonies of variable size.
Cultivation: The preference is dappled sunlight to light shade, moist to mesic conditions, and a rich loamy soil. The size of individual plants is strongly influenced by moisture conditions and the fertility of the soil. The seeds should be planted during the summer so that they will germinate during the fall.
Range & Habitat: Blue-Eyed Mary occurs occasionally in NE and east central Illinois, but it tends to be less common elsewhere (see Distribution Map). At some high quality sites around the state, it is locally abundant. Habitats include moist to mesic deciduous woodlands, wooded slopes of river valleys, and along woodland paths. Sometimes Blue-Eyed Mary occurs in drier woodlands, in which case the individual plants will be smaller in size. Even though it tolerates minor levels of disturbance, this plant is an indicator species of high quality woodlands.
Faunal Associations: The nectar and pollen of the flowers attract bumblebees and other long-tongued bees. Occasionally, butterflies and skippers visit the flowers, but they are less effective at cross-pollination. The caterpillars of the butterfly Celastrina argiolus (Spring/Summer Azure) feed on the flower buds and seed capsules of Blue-Eyed Mary. Little else appears to be known about floral-faunal relationships for this species.
Photographic Location: A mesic deciduous woodlands at Allerton Park in Piatt County, Illinois.
Comments: The distinctive bicolored flowers are very beautiful and they make Blue-Eyed Mary easy to identify. This woodland wildflower is unusual in having flowers with a true blue color. The only other species in the genus that has been observed in Illinois is Collinsia violacea (Violet Collinsia). This latter plant has violet flowers and lanceolate leaves. It prefers sunnier habitats and is quite rare within the state.