This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flowers - Pale violet blue, showy, about 2 in. long, solitary or clustered in the axils or at the end of stem. Calyx of 5 bristle-shaped hairy segments; corolla with very slender tube expanding above in 5 nearly equal obtuse lobes; stamens 4; 1 pistil with recurved style. Stem: Hairy, especially above, erect, 1 to 2 1/2 ft. high. Leaves: Opposite, oblong, narrowed at apex, entire, covered with soft white hairs.
Perferred Habitat - Dry soil.
Flowering Season - June - September.
Distribution - New Jersey southward to the Gulf and westward to Michigan and Nebraska.
Many charming ruellias from the tropics adorn hothouses and window gardens in winter; but so far north as the New Jersey pine barrens, and westward where killing frosts occur, this perennial proves to be perfectly hardy. In addition to its showy blossoms, which so successfully invite insects to transfer their pollen, thereby counteracting the bad effects of close in-breeding, the plant bears inconspicuous cleistogamous or blind ones also. These look like arrested buds that never open; but, being fertilized with their own pollen, ripen abundant seed nevertheless.
One frequently finds holes bitten in these flowers, as in so many others long of tube or spur. Bumblebees, among the most intelligent and mischievous of insects, are apt to be the chief offenders; but wasps are guilty too, and the female carpenter bee, which ordinarily slits holes to extract nectar, has been detected in the act of removing circular pieces of the corolla from this ruellia with which to plug up a thimble-shaped tube in some decayed tree. Here she deposits an egg on top of a layer of baby food, consisting of a paste of pollen and nectar, and seals up the nursery with another bit of leaf or flower, repeating the process until the long tunnel is filled with eggs and food for larvae. Then she dies, leaving her entire race apparently extinct, and living only in embryo for months. This is the bee which commonly cuts her round plugs from rose leaves.
The Smooth Ruellia (R. strepens), an earlier bloomer than the preceding, and with a more southerly range, has a shorter, thicker tube to its handsome blue flower, and lacks the hairs which guard its relative from crawling pilferers.