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B. S. Walters

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Swamps and shores, often in areas that are quite wet, at least seasonally, often dominant on floodplains, occasionally invading peatlands, also in upland deciduous forests and old fields.

Plants with leaves and new twigs glabrous have been called green ash, but are not now considered of sufficient taxonomic significance to warrant recognition as a variety or subspecies. Pubescent plants (red ash) are rather easily recognized, but glabrous ones may sometimes be confused with F. americana, especially when one does not have sufficient magnification to see the papillose lower surface of the leaflets in the latter. The distinctive slender petiolules in F. americana usually contrast well with the very short petiolules in F. pennsylvanica, in which furthermore they are often narrowly winged so as to give the leaflets an almost sessile aspect. The leaflets may be paler green beneath than above, but are only very rarely as whitish as in typical F. americana. Waxy flakes or strips peeling from year-old twigs of F. americana contrast with the usually smooth (if not pubescent) twigs of F. pennsylvanica. Natural hybrids between these two species are apparently very rare.

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