Platanus rzedowskii Nixon & J.M.Poole

Like Platanus glabrata, P. rzedowskii occupies the middle ground between the ranges of P. occidentalis (from central Texas northwards across the eastern United States and just into Canada) and of P. mexicana (sensu Nixon and Poole) from central Mexico into Guatemala; it is best understood as part of a complex of intermediate taxa (Grimm & Denk 2010). The species resembles P. mexicana more than P. glabrata does, since its leaves generally remain silvered underneath with a dense covering of stellate hairs, but its large fruit-balls, carried singly, are one featured linking it to P. occidentalis (unlike in P. occidentalis, the style tipping each seed is persistent, giving the fruit-ball the same spiky apperance as that of P. orientalis). Like P. glabrata but unlike either P. occidentalis or P. mexicana, the leaves of P. rzedowskii tend to carry five rather than three lobes, a feature which may indicate introgression with members of the ‘western clade’ of Platanus such as P. gentryi (not discussed here). One unusual feature among New World Platanus is the overall hairiness of the seed (achene) of P. rzedowskii, a feature which again happens to be shared with the European P. orientalis. Nixon & Poole (2003) also describe (but do not name) a population intermediate between P. rzedowskii and P. mexicana, which occurs in central eastern Mexico where the ranges of these species meet, and which they treat as hybrids; as of 2025, this population had not been described at either specific or varietal level.

As early as 1921, Paul Standley (Standley 1920–1924) described a Mexican plane with characteristically single seed-balls, but he treated this taxon as P. mexicana, instead using the names P. chiapensis, P. lindeniana and P. oaxacana for the trees described as P. mexicana by Nixon & Poole (2003). The name P. rzedowskii was first published by Kevin Nixon and Jackie Poole as a disambiguation, and commemorates the Polish-born Mexican botanist Jerzy Rzedowski Rotter (1926–2023; Nixon & Poole 2003).

Platanus rzedowskii is ‘one of the most distinctive and beautiful’ members of its genus (Nixon & Poole 2003). However, the name’s relative novelty makes it harder to confirm its presence in cultivation beyond its natural range. In 1973–74, Calvin McMillan studied the performance of seedling Mexican Platanus from Monterrey and Linares (Nuevo León) at the University of Texas at Austin (McMillan 1974); McMillan called these trees P. occidentalis, but they were still growing at Austin in the late 1980s when Nixon and Poole were able to verify then as P. rzedowskii (Nixon & Poole 2003). In northern Florida, Gary Knox considers P. rzedowskii an attractive alternative to P. occidentalis, which seems likely to mature as a somewhat smaller tree (Knox 2020). The plane-trees which have become popular as ornamentals in the San Antonio region of Texas are usually called P. mexicana, but seem likelier to represent P. rzedowskii (Wilson Landscape Nursery 2025): this is probably to be expected, since the wild populations of P. rzedowskii are fairly local to southern Texas, while the natural range of P. mexicana sensu Nixon and Poole lies far to the south. However, cultivated ‘P. mexicana’ in New Zealand show the three-lobed leaves typical of P. mexicana sensu Nixon and Poole, not the five lobes characteristic of P. rzedowskii.