Cladrastis kentukea (Dum.Cours.) Rudd — American yellowwood

Introduction

American yellowwood (Cladrastis kentukea) is a deciduous forest tree native to a scattered range from southern Illinois and Missouri through the central and southeastern United States. It is the only living yellowwood native to North America and the most distinctive member of the genus morphologically, with relatively few but unusually broad leaflets. Mature trees usually reach about 15–20 m, developing smooth gray bark and broad crowns. Large drooping panicles of fragrant white flowers open in late spring, followed by flattened, unwinged legumes (Johnson 2021; Royal Botanic Gardens, Kew 2026).

In the wild, American yellowwood is characteristically associated with rich woodland, river valleys, calcareous bluffs, and nutrient-rich slopes, often in cool or north-facing positions. It is nowhere uniformly common across its range. Its broad-leaved North American form contrasts strongly with the narrower-leaved East Asian species and represents one side of the classic eastern North America–East Asia disjunction in Cladrastis.

The accepted name has a complicated history. For much of the nineteenth and twentieth centuries the species was widely called Cladrastis lutea, based ultimately on Virgilia lutea. The older epithet in Sophora kentukea has priority, producing the current Cladrastis kentukea. Older names including C. lutea, C. fragrans, C. tinctoria, and several Virgilia combinations remain important historical synonyms (Royal Botanic Gardens, Kew 2026).

Horticultural and Agricultural Uses

American yellowwood is the principal ornamental species of the genus in North America. Its appeal comes from the combination of smooth gray bark, a broad architectural crown, fresh green pinnate foliage, fragrant white flowers, and autumn colors that can range from yellow through orange. Trees are very cold hardy, but flowering depends strongly on age and climate. Seedlings often require many years before first flowering, and established trees may produce spectacular displays only every few years rather than annually (Johnson 2021).

The species prefers deep, fertile, well-drained soils with adequate moisture and is especially compatible with calcareous or alkaline sites resembling many of its natural habitats. Its deep rooting can make established specimens difficult to transplant. Because mature trees can develop broad crowns and major structural limbs, they are better suited to lawns, parks, arboreta, and large gardens than to confined planting spaces.

Several horticultural selections have been named, most notably the pink-flowered ‘Perkins Pink’. Such cultivars represent selected ornamental clones, not botanical varieties or subspecies.

American yellowwood also has a modest historical timber history. The heartwood gives the yellow coloration that inspired the common name and has been used as a source of dye and for specialty wood products. Physiologically, the species is notable within Fabaceae because experimental inoculation failed to induce nitrogen-fixing root nodules (Foster et al. 1998).

Conservation Concerns

American yellowwood is globally assessed as Least Concern, but its natural distribution is fragmented and the species is much less ubiquitous in the wild than its horticultural familiarity might suggest. NatureServe assigns a global rank of G4, Apparently Secure, while noting that the species is rare through much of its range outside Arkansas and Kentucky. Habitat modification, forest conversion, clearcutting, and development have affected some populations (NatureServe 2026).

NatureServe’s most recent assessment also indicates an estimated short-term decline and reports probable loss of at least one historically known population in Louisiana. Cultivated abundance outside the natural range therefore should not be used as a substitute for conserving the scattered native populations and their geographic genetic diversity.

Additional Information

Plants of the World Online (opens in a new tab): Accepted taxonomy, native and introduced ranges, and extensive synonymy.
Trees and Shrubs Online (opens in a new tab): Detailed morphology, nomenclatural history, cultivation, and cultivars.
NatureServe Explorer (opens in a new tab): Current global rank, distribution, habitat, and threat assessment.

References and Further Reading

Foster CM, Horner HT, Graves WR (1998) Nodulation response of woody Papilionoid species after inoculation with rhizobia and soil from Hawaii, Asia and North America. Plant and Soil 205(2): 103–111. DOI 10.1023/A:1004309414388 (opens in a new tab).

Johnson O (2021) Cladrastis kentukea. Trees and Shrubs Online.

NatureServe (2026) Cladrastis kentukea. NatureServe Explorer.

Royal Botanic Gardens, Kew (2026) Cladrastis kentukea (Dum.Cours.) Rudd. Plants of the World Online.