A western species, L. redowskii (Hornem.) Greene, has frequently been reported to range into Michigan as a waif, but all specimens so labeled are better referred to L. squarrosa (with even immature fruit showing 2 rows of marginal prickles). Each nutlet of L. redowskii has only a single row of marginal prickles and hence appears distinctly less prickly than in our species, which also tends to have larger nutlets and stems with more appressed pubescence.