Stem. - Slender, branching. Leaves. - Lance-shaped to linear, the floral ones heart-shaped and clasping, folding so as to enclose the flowers. Flowers. - Blue. Calyx. - Of three unequal somewhat colored sepals, the two lateral ones partly united. Corolla. - Of three petals, two large, rounded, pale blue, one small, whitish, and inconspicuous. Stamens. - Six, unequal in size, three small and sterile, with yellow cross-shaped anthers, three fertile, one of which is bent inward. Pistil. - One.

The odd day-flower is so named because its delicate blossoms only expand for a single morning. At the first glance there seem to be but two petals which are large, rounded, and of a delicate shade of blue. A closer examination, however, discovers still another, so inconspicuous in form and color as to escape the notice of the casual observer. This inequality recalls the quaint tradition as to the origin of the plant's generic name. There were three brothers Commelin, natives of Holland. Two of them were botanists of repute, while the tastes of the third had a less marked botanical tendency. The genus was dedicated to the trio: the two large bright petals commemorating the brother botanists, while the small and unpretentious one perpetuates the memory of him who was so unwise as to take little or no interest in so noble a science. These flowers appear throughout the summer in cool woods and on moist banks.