Cladrastis (yellowwood) is a genus of flowering plants in the family Fabaceae (order Fabales), comprising four species of deciduous trees — three native to eastern Asia and one to southeastern North America. The trees are small to medium-sized, typically reaching 10–20 m (30–50 ft) tall, with a broad rounded crown and upright branching. The leaves are pinnately compound with 5–17 alternately arranged leaflets that emerge yellowish green, mature to bright green, and turn yellow in autumn. Fragrant, wisteria-like white or pink flowers are produced in large drooping racemes or panicles 15–40 cm (10–15 inches) long in late spring, though profuse blooming may only occur every 2–3 years. The fruit is a flat pod 3–8 cm long containing one to six seeds. The wood of the American species contains a yellow dye that colors the heartwood, giving the genus its common name. Cladrastis is closely related to Maackia, from which it differs in having buds concealed in the leaf base and alternately arranged leaflets. Together with Pickeringia and Styphnolobium, it forms the Cladrastis clade — though the genus itself is paraphyletic as the other two genera originated from within it.
Etymology
The genus name Cladrastis derives from the Greek klados (branch) and thraustos (fragile), referring to the brittle nature of the twigs. The common name “yellowwood” comes from the yellow dye found in the heartwood. The American species was formerly classified as Cladrastis lutea (lutea meaning yellow).
Distribution
The genus has a disjunct distribution: three species are native to eastern Asia (C. delavayi in the Himalayas to central China, C. shikokiana in southern Japan, and C. wilsonii in central China), while one species, C. kentukea, is native to the southeastern United States, including the Ozark region of Missouri.
Taxonomy
Cladrastis, Pickeringia, and Styphnolobium form a monophyletic group known as the Cladrastis clade within the tribe Sophoreae of Fabaceae. However, because both Pickeringia and Styphnolobium originated from within Cladrastis, the genus is paraphyletic. Cladrastis is closely related to the genus Maackia, differing in its concealed buds and alternately (rather than oppositely) arranged leaflets on the leaf rachis.
Cultivation
Cladrastis kentukea is easily grown in average, medium-moisture, well-drained soils in full sun, tolerating some dryness once established. It is hardy in USDA zones 4–8 with low maintenance needs. Site in a location protected from strong winds, as the branches are brittle and vulnerable to ice and snow damage. Pruning should be done in summer, as cuts made in late winter or spring tend to bleed. Deep roots allow underplanting. Potential problems include Verticillium wilt, bark sun scald, and late spring frost damage to blooms. Trees may take 8–10 years to begin flowering and may bloom profusely only every 2–3 years. Excellent as a small shade or flowering tree for residential lawns, patios, and terraces.
