3. Catalpa (catalpa)

Plants trees or less commonly shrubs, lacking tendrils. Twigs stout, glabrous or sometimes hairy when young, yellowish to reddish brown, with prominent white lenticels, the leaf scars prominent. Leaves opposite or whorled, simple, long-petiolate. Leaf blades ovate, sometimes shallowly 3-lobed or 3-angled toward the base, cordate or less commonly truncate at the base, narrowed or tapered to a sharply pointed tip, the margin otherwise entire. Inflorescences large, terminal panicles. Calyces splitting deeply into two irregular lobes at maturity, glabrous, usually purplish-tinged, the lobes broadly ovate, pointed at the tip. Corollas zygomorphic, glabrous, 5-lobed, appearing obliquely 2-lipped, white or light yellow with 2 longitudinal yellow to orange lines and a pattern of purple to brownish purple spots and short lines in the throat, the tube bell-shaped, the lobes shorter than the tube, the margins irregular and appearing somewhat crinkled. Stamens 2 or rarely 4. Staminodes 3 (or 1 in flowers with 4 stamens), minute, fused to the corolla tube. Fruits cylindrical, circular in cross-section, glabrous, brown at maturity. Seeds flattened, elliptic in outline, 2-lobed, light brown, with a long tuft of dense hairs at each end, each tuft fused toward the base into a papery wing. Ten species, U.S., Caribbean Islands, Asia.

Catalpas are the required food source for caterpillars of the catalpa sphinx moth (Ceratomia catalpae Boisd.), which can entirely defoliate trees during peak years but are usually heavily parasitized themselves by small wasps. The flowers are pollinated primarily by carpenter bees (Xylocopa spp.) and secondarily by bumblebees and honeybees. The North American catalpas are frequently cultivated as shade trees and ornamentals. The wood is a minor source of fence posts, rails, poles, and lumber for furniture, and it is sometimes mixed with other woods to make pulp for paper. The leaves turn yellow or brown in the autumn.

Cox and Dunn (1973–1974) and Cox (1973–1974) studied catalpa trees growing under cultivation and as escapes in Columbia (Boone County), where they documented putative introgression between the three species treated below. Based on a morphological analysis and the electrophoretic study of seed proteins, they identified individuals of C. bignonioides H C. ovata, C. bignonioides H C. speciosa, and C. ovata H C. speciosa, as well as putative backcrosses to the parental taxa. Hybrids were noted to form viable seeds but had greatly reduced fruit set. The hybrid between C. bignonioides and C. ovata originally was developed in the horticultural trade through artificial crosses and has been named C. Herubescens Carrère (C. Hhybrida Späth). In nature, these trees rarely if ever grow together, at least in Missouri. Thus, there is little likelihood of hybridization in more natural settings.