The lowest floral leaf is the lowest leaf on the main stem with a flower or capsule associated with it. The teeth are in pairs, one at either edge of the leaf. Most Euphrasia have white or lilac flowers so this characteristic is only of limited help in distinguishing the species. Nevertheless, as flower colour is easily and reliably determined it is worth using it in the key. The corolla can be gently pulled from the calyx and measured across the top.
Some species have a few long hairs on the under side of the lower lip of the corolla.
The primary months for flowering are July and August though some species can flower as early as May and as late as September. As there is only limited variability in the flowering times of Euphrasia this character will only of be of use in occasional circumstances. Cauline internodes are the lower internodes on the stem without flowers in the axils of the leaves. Divide the length of these internodes by the leaf length. A simple estimate of this parameter can be made by bending the leaf up against the stem.