This is a very distinctive genus in several morphological characters; perhaps the most obvious is the little crest (scutellum, literally a little shield) across the top of the calyx, the origin of the generic name.
1. Flowers all in axillary or terminal racemes (i.e., in axils of small bracts); principal leaves with petiole over 4 mm long (3–4 mm only on depauperate individuals).
2. Racemes chiefly axillary; flowers (4.5–) 5.5–7.5 (–8.5) mm long.
2. Racemes chiefly terminal; flowers ca. 11–16 (–20) mm long.
3. Principal cauline leaves with blade essentially lacking glandular dots beneath, strongly cordate, the lobes extending well below any tissue decurrent on the petiole.
3. Principal cauline leaves with blade glandular-dotted beneath, truncate or rounded at the base, usually with tissue decurrent on the petiole.
4. Calyx and bracts of inflorescence with some long, spreading, gland-tipped hairs.
4. Calyx and bracts with only very short, ± appressed or incurved, eglandular hairs.
1. Flowers in the axils of cauline leaves ± gradually (if at all) reduced in size; principal leaves with petioles none or less than 4 mm long.
5. Corolla (13–) 16–22 mm long; mid-cauline leaves (1.8–) 2.5–5.5 (–8) cm long, including distinct petiole 0.5–3.4 (–4) mm long.
5. Corolla 6–11 mm long; mid-cauline leaves ca. 1–4 cm long, sessile or on petioles less than 0.7 mm long.
6. Stem (middle internodes) glabrous or with a few scattered hairs; principal leaf blades ca. (1.5–) 2.2–4 cm long, with a few definite teeth on each side; corolla white to pale blue, ca. 9–11 mm long.
6. Stem puberulent or ± pilose; leaf blades 1–1.8 cm long, essentially entire; corolla deep blue to purple, ca. 6–9 mm long.