Dayflower, the common name of a genus of about 200 species of perennial herbaceous plants of tropical and subtropical climates. The dayflower is so named because each of its flowers opens for one day only. The stems may be erect, or reclining with upright branches. The leaves are alternating and grasslike. The flowers have three petals and protrude from a heart-shaped bract (a specialized leaf) at the top of the stem. Dayflowers are commonly grown for ornamental purposes or as ground cover.
The western dayflower, ranging from Texas to Colorado, has blue flowers and is about 20 inches (50 cm) tall. The Asiatic dayflower, introduced into America from Asia, ranges from Massachusetts to Alabama and west to Kansas; it has blue and white flowers and a reclining stem that is about three feet (90 cm) long.
Dayflowers make up the genus Commelina of the spiderwort family, Commelinaceae. The western dayflower is C. dianthifolia; Asiatic, C. communis.