Flora of North America species comparison

Wisteria × formosa originated spontaneously about 1905 at Holm Lea, the 150-acre estate owned by botanist Charles Sprague Sargent in Brookline, Massachusetts. The hybrid grew from seed borne by a white-petaled plant of W. floribunda; the pollen parent was assumed to have been W. sinensis, which was also cultivated on the estate. As an ornamental, it is regarded as superior to both parents, with large, fragrant flowers, and sequential anthesis combined with precocious blooming of W. sinensis (A. J. Rehder 1922).

Wisteria ×formosa has been a source of confusion for botanists. Although D. Wyman (1949, 1969, 1977) indicated that it is more common in American horticulture than either parent, no major North American flora has included it in its keys and descriptions. As a result, its existence in the spontaneous flora of the continent has gone unrecognized. For example, D. Isely (1990) experienced difficulty in attempting to discriminate W. floribunda from W. sinensis in the southeastern United States. The lack of consistent character-state correlations he noted is exactly what would be seen if much of the studied material was actually W. × formosa, as was borne out by molecular studies of weedy Wisteria in the southeastern United States (J. L. Trusty et al. 2007).

(Discussion copyrighted by Flora of North America; reprinted with permission.)