Hackelia

The pedicels in our species of both genera tend to be supra-axillary and the exposed faces of the nutlets are rough-papillose besides whatever bristles are present. The tiny inconspicuous flowers and bur-like fruits do not encourage collectors and both species are doubtless less scarce than the maps suggest.

1. Exposed face of nutlets with barb-tipped bristles only around the margins (at most a few tiny ones in the middle); widest cauline leaves (0.8–) 1–2.5 (–5) cm broad; pubescence of uppermost internodes and branches of the inflorescence closely appressed; corolla blue.

H. deflexa

1. Exposed face of nutlets covered with several barb-tipped bristles nearly or quite as large as the marginal ones; widest cauline leaves (2.5–) 3–5 (–9.5) cm broad; pubescence of uppermost internodes and branches of the inflorescence partly spreading-ascending; corolla white.

H. virginiana