This reportedly tetraploid species (2n = 80) has a fairly wide northeastern range, but it is largely restricted to seasonally wet sites on base-rich soils. It is rare to absent in most of the unglaciated Ohio Rv. watershed (K). In Ky. it is verified as native only from a few sites in western regions; but it is sometimes planted in wildflower displays. There has been some confusion with torreyi, which mostly occurs further east in Ky. and on drier sites, but still within the former Big Barrens region. Some colls. originally identified as virginianum from CALL, HARD and LIVI have been transferred to torreyi, and others should be rechecked. P. virginianum differs from torreyi as follows (F, W; Chambers 1993): shorter calyx teeth (ca. 0.7-1 mm versus 1-2 mm), often tighter capitula (versus lower branches evident), stems with hairs largely resticted to angles (versus more or less evenly distributed but longer on angles), and generally narrower leaves (mostly 3-10 mm versus 8-12 mm). Superficially it appears intermediate between pilosum (or verticillatum) and tenuifolium, with diagnostic characters being stem pubescence (versus usually glabrous to sparsely hairy in tenuifolium) and leaf width (versus mostly 2-5 mm in tenuifolium). Indeed, some plants referrable to virginianum in Ky. may be interpreted as hybrids between the generally more common pilosum and tenuifolium.