Platyosprion (Maxim.) Maxim. — False-yellowwood

Treatment and Overview

Platyosprion, false-yellowwood, is a monotypic genus of deciduous trees in the Legume Family (Fabaceae), represented today by Platyosprion platycarpum of eastern Asia. The genus belongs to Papilionoideae and the early-diverging tribe Cladrastideae. Although false-yellowwood was placed in Cladrastis through much of the twentieth century, modern phylogeny supports Platyosprion as an independent evolutionary lineage best-treated at the genus level (Duan et al. 2019; Royal Botanic Gardens, Kew 2026).

The name Platyosprion predates its merger into Cladrastis. Maximowicz first recognized Platyosprion as a subgenus of Sophora in 1873 and subsequently elevated it to genus rank. IPNI records the genus as Platyosprion (Maxim.) Maxim. and dates the genus-rank publication to 1877. Current Plants of the World Online displays an 1876 publication date, a bibliographic discrepancy that does not affect acceptance or circumscription of the genus (International Plant Names Index 2026; Royal Botanic Gardens, Kew 2026).

Its later association with Cladrastis was understandable. Both lineages have smooth gray bark, compound leaves with alternately positioned leaflets, buds concealed within swollen petiole bases, and white papilionoid flowers. False-yellowwood differs consistently in features that include small stipels at the leaflet bases, relatively small flowers, and especially its flattened fruits with broad marginal wings. These distinctions correspond to a genuine phylogenetic separation rather than merely to unusual morphology within Cladrastis (Duan et al. 2019).

Most importantly, Platyosprion and Cladrastis are not sister genera. In the focused reconstruction of Cladrastideae, Platyosprion represents an earlier-diverging lineage, whereas Cladrastis is more closely associated with the branch containing Pickeringia (chaparral-pea) and Styphnolobium (false-necklacepod; pagoda-tree). Their long taxonomic association therefore illustrates how retention of ancestral or superficially similar morphology can obscure deeper relationships (Duan et al. 2019, 2020).

A surviving wing-fruited lineage

The winged fruit that gives false-yellowwood its most obvious generic character may also preserve something of the ancestral condition for Cladrastideae. Fossil-calibrated reconstruction inferred the common ancestor of the broader clade as a deciduous North American tree with compressed, winged fruits in the early Eocene. Platyosprion diverged early and retained a strongly winged legume, while the lineage leading to modern Cladrastis subsequently evolved unwinged fruits (Duan et al. 2020).

Modern Platyosprion is entirely East Asian, but that distribution appears to represent survival rather than geographic origin. The lineage was reconstructed as reaching Asia during the Eocene after an origin in North America, then disappearing from North America around the Eocene–Oligocene climatic transition as vegetation changed markedly with global cooling (Duan et al. 2020). False-yellowwood is thus the surviving eastern Asian representative of a lineage with a much broader Paleogene history.

Recognition of Platyosprion also demonstrates that molecular taxonomy does not simply divide taxa into ever-smaller units. Restoring the genus split broad Cladrastis at generic rank, but the same integrative analysis lumped four proposed species from the false-yellowwood complex into the single P. platycarpum. Generic recognition and species delimitation moved in opposite directions because they addressed different evolutionary questions (Duan et al. 2019).

Horticultural and Agricultural Uses

False-yellowwood remains a rarity in Western horticulture. Genuine trees, such as those at the Arnold Arboretum in Boston, MA have nevertheless demonstrated that the genus can produce graceful, medium to large flowering specimens in temperate collections. Its smooth bark, pinnate foliage, erect clusters of white flowers, winged fruits, and autumn color give it ornamental merit, while established cultivated specimens indicate substantial cold tolerance (Johnson 2021).

Historical misidentification is unusually important horticulturally. Plants labeled Cladrastis platycarpa have sometimes proved to be Styphnolobium japonicum (Japanese pagoda-tree) or other look-alikes, while genuine material survived under outdated Cladrastis labels. Provenance and diagnostic examination are therefore especially useful when bringing older arboretum records into the modern Platyosprion concept.

Conservation Issues

Because Platyosprion contains a single living species, the persistence of P. platycarpum also determines the survival of the entire genus. That species is currently assessed as Least Concern and occupies a substantial East Asian range, so the genus is not presently regarded as globally threatened (Royal Botanic Gardens, Kew 2026).

Its conservation significance nevertheless exceeds a simple species count. Platyosprion represents an early branch of Cladrastideae whose North American history ended tens of millions of years ago. Protecting geographically representative populations in China, Korea, and Japan therefore preserves not only one species but the sole surviving expression of a distinct ancient lineage.

Accepted Taxa

Accepted taxa of Platyosprion

Platyosprion platycarpum	(Maxim.) Maxim.	False-yellowwood

Additional Information

Plants of the World Online (opens in a new tab): Accepted monotypic genus, distribution, and current global taxonomic backbone.
International Plant Names Index (opens in a new tab): Nomenclatural record for Platyosprion (Maxim.) Maxim. and its link to Sophora subgen. Platyosprion.
Trees and Shrubs Online (opens in a new tab): Generic morphology, taxonomic history, relationships, and cultivation context.
Flora of China (opens in a new tab): Useful morphology for the false-yellowwood complex, but published under the older broad Cladrastis concept.

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 (opens in a new tab).

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 (opens in a new tab).

International Plant Names Index (2026) Platyosprion (Maxim.) Maxim. International Plant Names Index.

Johnson O (2021) Platyosprion. Trees and Shrubs Online.

Royal Botanic Gardens, Kew (2026) Platyosprion Maxim. Plants of the World Online.