The main picture above shows a stalk of E. graminifolia (top) for comparison. I found both species growing side by side in a relict sand dune community. In the field, extremes of the two species were quite distinct: E. graminifolia was always taller, more bright green, and with wider leaves and hairy stems. Plants of E. caroliniana were shorter in height and tended to grow in distinct colonies (in which the occasional stalk of E. graminifolia stood out like a sore thumb); the leaves were darker green and thinner (2-4mm wide), and the stems were more often glabrous (though occasionally sparsely hairy, but never finely pubescent like some forms of E. graminifolia). The heads were also more likely to be borne singly on pedicels in E. caroliniana, whereas in E. graminifolia the heads were always clustered.

As I said above, I've chosen to present the "extremes" in form here. There were intermediates galore, and while it is easy to say which species a given specimen resembles most, it is less easy (for me anyway) to draw the line separating the two. In my eyes at least, this is a continuum, and if these are really two distinct species then I would venture to say that hybridization is rampant wherever the two grow together (and they seem to grow together more often than not...).

Interestingly, E. caroliniana is said to have copious dark glands on the leaves. As far as I can tell with my 20x hand lens, this population lacked such dense glandularity, but some plants had a paler, glutinous film on the leaves -- I don't know if I am misinterpreting this or what, but when I read "dark glands" I think of those found on Hypericum punctatum or something, so I don't know...