Lithospermum mirabile is frequently confused with Lithospermum incisum. This is because the two species have similar flowers (yellow salverform corollas with tubes frequently longer than 1 cm) and overlapping geographic ranges; however, the flowers can actually differentiated quite easily. Lithospermum mirabile has corolla lobes that are entire (not fringed), while those of L. incisum are fimbriate (fringed). Both species also produce cleistogamous flowers.
The fruits of L. mirabile differ from those of other species of Lithospermum. While most species of the genus bear fruits that are smooth or perhaps have some pitting, the nutlets (fruits) of L. mirabile are rugose, which is another manner in which L. mirabile can be distinguished from L. incisum.
