Exacum

In Exacum and in Saintpaulia the flowers are dimorphic in this sense: the style projects to either the right or the left side of the corolla, from which it follows that a right-handed flower would fertilise a left-handed one, and vice versa.

More Letters of Charles Darwin — Volume 2 Charles Darwin 1845

Potentilla _tormentilla_ (indicating that the plant is that which was formerly known by the latter name), Exacum _Candollii_ (from the fact that

A System Of Logic, Ratiocinative And Inductive John Stuart Mill 1839