Also called “Wandering Jew,” and a close relative of the Wandering Jew often found in supermarket hanging baskets. This is the Asiatic Dayflower: the two upper petals are pure blue; the lower one is white. Virginia Dayflower, a native but rarer species, has a blue lower petal. The flowers close in the late afternoon; thus the name. We find this common flower everywhere, blooming all summer till frost; here it was blooming beside a front porch in Beechview.
Gray describes the genus and the species:
COMMELINA [Plum.] L. DAY-FLOWER
Flowers irregular. Sepals somewhat colored, unequal; the 2 lateral partly united. Two lateral petals rounded or kidney-shaped, on long claws, the odd one smaller. Stamens unequal, 3 of them fertile, one of which is bent inward; 3 of them sterile and smaller, with imperfect cross-shaped anthers; filaments naked. Often procumbent and rooting at the joints. Leaves contracted at base into sheathing petioles; the floral one heart-shaped and clasping, folded together or hooded, forming a spathe inclosing the flowers, which expand for a single morning and are recurved on their pedicel before and afterward. Petals blue. Flowering all summer. Ours all with perennial roots, or propagating by striking root from the joints. (Dedicated to the early Dutch botanists J. and G. Commelin.)
C. communis L. Slender and creeping, nearly glabrous; leaves lanceolate, 2-5 cm. long; spathe cordate, acute, with margins not united; seeds shallowly pitted, granulate-reticulated. (C. nudiflora auth., not L.) Alluvial banks, Del. to Fla., w. to Kan. and Tex. A frequent weed of dooryards and gardens, northeastw. to e. Mass. (E. Asia, Trop. reg.)
Flora Pittsburghensis 
And it’s now in California because I brought some back from a trip to Sugarloaf in Maryland in 1998. It’s at my mother’s house in Modesto and mine in Petaluma.