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Cladrastis Raf.

Yellowwood

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Treatment and Overview

Cladrastis, the yellowwoods, is a small genus of four deciduous trees in the Legume Family (Fabaceae). Three species are native to eastern Asia and one, American yellowwood (Cladrastis kentukea), is native to eastern North America. All four species are small to medium-sized trees. Yellowwoods share smooth gray bark, pinnately compound leaves with the leaflets characteristically arranged alternately rather than oppositely along the rachis, buds concealed during the growing season within swollen petiole bases, white papilionoid flowers, and flattened legumes without conspicuous marginal wings (Duley & Vincent 2003; Duan et al. 2019). Tree TSAR follows the current global consensus in recognizing C. delavayi, C. kentukea, C. shikokiana, and C. wilsonii (Royal Botanic Gardens, Kew 2026). These species are not to be confused with members of the conifer genus Afrocarpus (Podocarpaceae); these tropical gymnosperms are often called “yellowwood” and the genus has a standardized Tree TSAR common name of “African-yellowwood.”

True yellowwoods and false-yellowwood

The modern circumscription of Cladrastis is narrower than the concept familiar from much of the twentieth-century literature. One species complex, formerly known as Japanese yellowwood (Cladrastis platycarpa), is now placed in its own monotypic genus, Platyosprion (false-yellowwood). This tree resembles the true yellowwoods in bark, foliage, concealed buds, and general floral architecture, but also has some key morphological differences. Despite similarities, molecular analyses nevertheless demonstrated that broad Cladrastis was not a natural genus. Duan et al. (2019) recovered four major lineages in the group and resurrected Platyosprion for the wing-fruited C. platycarpa complex, leaving Cladrastis sensu stricto as a coherent four-species genus.

The historical association between yellowwood and false-yellowwood is therefore biologically understandable but phylogenetically misleading. In the focused reconstruction of the clade, Platyosprion diverged earlier, while Cladrastis was more closely associated with the lineage containing Pickeringia (chaparral-pea) and Styphnolobium (false-necklacepod; pagoda-tree). Yellowwood and false-yellowwood are consequently not sister genera, despite having been combined taxonomically for much of the last century (Duan et al. 2019, 2020). Broader nuclear phylogenomics continues to support Cladrastideae as an early-diverging papilionoid lineage, although relationships among the deepest branches of Papilionoideae are part of a much larger history of genomic conflict in legumes (Zhang et al. 2026).

The morphological distinction is useful in living plants. Cladrastis lacks the small stipels normally present at the bases of the leaflets in Platyosprion, its leaflets commonly become paler or grayish beneath, and its mature fruits are compressed but unwinged. Platyosprion has smaller flowers and conspicuously winged legumes. These differences make the modern generic split recognizable without DNA once their evolutionary significance is understood (Duan et al. 2019).

An ancient North American lineage with an Asian history

The present eastern North America–East Asia disjunction is the surviving fragment of a much broader Paleogene history. Fossil-calibrated reconstruction places the ancestral Cladrastideae lineage in mid-latitude North America during the early Eocene. That ancestor was reconstructed as a deciduous tree with compressed, winged fruits. The conspicuous fruit wings retained by Platyosprion may therefore approximate the ancestral condition, whereas the unwinged legumes of Cladrastis sensu stricto represent a subsequent transformation (Duan et al. 2020).

The ancestors of Cladrastis apparently reached eastern Asia during the Eocene through northern intercontinental connections. Beringia is a plausible route, although North Atlantic connections cannot be excluded. Fossil evidence now independently supports an early Asian presence. Cladrastis haominiae, described from the Huazhige Formation of southeastern Yunnan, preserves an infructescence and fruits closely comparable with modern yellowwoods and demonstrates that Cladrastis was established in Asia by the Paleogene, probably by the late Eocene (Jia et al. 2021).

Older North American fossils assigned to Cladrastis require more caution. Some possess winged fruits and were named before the modern distinction between Cladrastis and Platyosprion was understood. Such fossils may represent stem Cladrastideae or a Platyosprion-like lineage rather than crown Cladrastis sensu stricto. The fossil record is consequently most informative as evidence of a formerly wider northern-hemisphere radiation rather than as a simple list of extinct species belonging unquestioningly to the modern genus (Duan et al. 2020; Jia et al. 2021).

No useful formal infrageneric classification is presently warranted within the four-species genus. Older sectional systems chiefly separated the wing-fruited Platyosprion complex from true Cladrastis. Once Platyosprion is recognized as a genus, that division ceases to describe internal structure within Cladrastis. The three East Asian species form a convenient biogeographic assemblage, but their internal relationships are not yet resolved strongly enough to justify new subgenera or sections (Duley & Vincent 2003; Duan et al. 2019).

Yellowwoods also illustrate an important exception to the familiar association between legumes and nitrogen fixation. In experimental inoculations, C. kentukea failed to form root nodules, consistent with earlier observations that nodulation had not been documented in Cladrastis (Foster et al. 1998). This does not imply that every species has been subjected to equivalent experimental testing, but it places the genus among the papilionoid lineages in which the familiar rhizobial symbiosis is absent or unconfirmed.

Horticultural and Agricultural Uses

Yellowwoods are primarily ornamental and collection trees rather than agricultural plants. American yellowwood is by far the best known in North American horticulture. Its broad crown, smooth gray bark, large pinnate leaves, fragrant white flowers, and yellow to orange autumn color make it an exceptional specimen tree where adequate space is available. Chinese yellowwood is less familiar but can be equally ornamental, flowering later in the summer and often more reliably in climates with sufficient warmth. The other two species, C. shikokiana and C. wilsonii, remain exceptionally scarce in Western collections (Johnson 2021, 2023).

Yellowwoods generally perform best in deep, fertile, well-drained soils with reliable moisture, and both the American and Chinese species tolerate calcareous or alkaline substrates. Flowering can be strongly affected by climate and maturity. C. kentukea may take many years to begin blooming and can flower heavily only at intervals, while C. delavayi benefits from summers warm enough to ripen its growth even where winters themselves are relatively mild (Johnson 2021).

Correct identification is especially important in living collections. Several trees cultivated in Europe and North America as C. wilsonii have proved or are suspected to be other yellowwoods, and historical collections of Platyosprion have likewise circulated under Cladrastis. Wild provenance, accession history, and voucher material add unusual value to cultivated specimens of the rarer Asian species.

Conservation Issues

No single conservation status describes the genus adequately. Cladrastis kentukea, C. delavayi, and C. wilsonii are treated as Least Concern in current global or authoritative summaries, but the American species occurs naturally in scattered populations and remains vulnerable locally to forest conversion and habitat alteration. NatureServe ranks C. kentukea G4, “apparently secure,” while documenting rarity through much of its range and an estimated recent decline associated partly with habitat loss (NatureServe 2026).

The conservation picture is more concerning for C. shikokiana. It has not received a global IUCN assessment, but Japanese regional Red Data Books identify substantial local rarity: the species is listed as Vulnerable in Tokyo and Yamaguchi, Critically Endangered in Fukuoka, Near Threatened in Wakayama, and regionally extinct in Kanagawa. These regional assessments indicate that a lack of global evaluation should not be interpreted as evidence of security (National Red Data Search System 2026).

For the rarer Asian yellowwoods, accurately documented wild-origin collections have conservation value beyond ornamental display. Provenance-rich living material can preserve geographic diversity, support future genomic work, and reduce the taxonomic ambiguity created when cultivated trees are maintained under names that may not correspond to their actual identities.

Accepted Taxa
Cladrastis delavayi (Franch.) Prain Chinese yellowwood
Cladrastis kentukea (Dum.Cours.) Rudd American yellowwood
Cladrastis shikokiana (Makino) Makino Yukunoki yellowwood
Cladrastis wilsonii Takeda Wilson yellowwood

Additional Information

References and Further Reading

Duan L, Harris AJ, Ye W, Deng S-W, Song Z-Q, Chen H-F, Wen J (2019) Untangling the taxonomy of the Cladrastis clade (Leguminosae: Papilionoideae) by integrating phylogenetics and ecological evidence. Taxon 68(6): 1189–1203. DOI 10.1002/tax.12155.

Duan L, Harris AJ, Su C, Ye W, Deng S-W, Fu L, Wen J, Chen H-F (2020) A fossil-calibrated phylogeny reveals the biogeographic history of the Cladrastis clade, an amphi-Pacific early-branching group in papilionoid legumes. Molecular Phylogenetics and Evolution 143: 106673. DOI 10.1016/j.ympev.2019.106673.

Duley ML, Vincent MA (2003) A synopsis of the genus Cladrastis (Leguminosae). Rhodora 105: 205–239.

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.

Jia L-B, Huang J, Su T, Spicer RA, Zhang S-T, Li S-F, Pan B, Nam G-S, Huang Y-J, Zhou Z-K (2021) Fossil infructescence from southwestern China reveals Paleogene establishment of Cladrastis in Asia. Review of Palaeobotany and Palynology 292: 104456. DOI 10.1016/j.revpalbo.2021.104456.

Royal Botanic Gardens, Kew (2026) Cladrastis Raf. Plants of the World Online.

Zhang R, Stull GW, Jin J-J, Wang Y-H, Guo Y, Yang Z-Y, Li H-T, An K-L, Charboneau JLM, Folk RA, et al. (2026) Phylogenetic resolution and conflict in the species-rich flowering plant family Leguminosae. Systematic Biology 75(2): 236–258. DOI 10.1093/sysbio/syaf057.