A tree sometimes over 100 ft high in a wild state, with a tall trunk 10 ft or more in circumference. Leaves inodorous, ovate, with a heart-shaped or rounded base, and a long, tapering point; 5 to 12 in. long, 3 to 8 in. wide; nearly or quite glabrous above when mature, covered beneath with pale brown down. Panicles about 6-8 in. long, rather more wide, with comparatively few flowers. Corolla white, 2 in. long and wide, the tube bell-shaped, the lobes spreading and frilled at the margin; the lower one with yellow spots and ridges as in C. bignonioides, but less freely spotted with purple. Seed-vessel 8 to 18 in. long, 1⁄2 in. or little more wide.
Native of the United States, found only west of the Alleghanies and extending further north in the Mississippi Basin than C. bignonioides; introduced in 1880. It differs from that species in its taller growth, its longer, more tapering, inodorous leaves, and in its flowers being larger, fewer in the panicles, and less profusely purple-spotted. At Kew it flowers well in July, two weeks in advance of the other, and promises to make a taller tree, of more upright habit. The largest in the collection measures 60 × 43⁄4 ft (1963). There is another in Radnor Gardens, Twickenham, measuring 55 × 93⁄4 ft (1967).
In the United States the timber of this tree is much valued on account of its extraordinary durability in contact with the ground and with moisture. Sargent mentions in the Silva of North America, Vol. vi, p. 90, a remarkable proof of this quality:
‘The trunks of catalpa trees killed by the sinking and subsequent submersion of a large tract of land near New Madrid, Missouri, which followed the earthquake of August 1811, were standing and perfectly sound sixty-seven years later, although all their companions in the forest had disappeared long before.’
Gate posts, too, have been known to stand in perfect preservation fifty to one hundred years. Railway companies in the United States are now planting it largely, to provide a future supply of railway sleepers.