This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The spike is dense as a rule. The flowers are whitish. The bracts are broadly ovate, acute, with 8-14 acute teeth. The calyx has small stiff bristles, and glandular and lance-shaped, narrowly-pointed teeth. The corolla is small, the lobes of the upper lip entire or notched. The capsule is elliptic, notched, fringed with hairs.
This plant is without hairs or slightly, softly downy. The stem is stout, simple, or but little branched. The leaves bear few hairs. The stem-leaves are few, distant, ovate, blunt, with 4-6 blunt teeth. The spike lengthens a little. The flowers are purple. The bracts are not so large as in the last, and rather distant, sometimes acute, with acute-pointed teeth. The calyx is devoid of hairs, or there may be a few bristles, and the teeth are triangular to lance-shaped. The corolla is small,with the lobes of the upper lip entire. The capsule is elliptic, long, notched, fringed with hairs, longer than the calyx-teeth.
The habitat of this plant is limestone pavements and cliff's, walls, sand-dunes, or non-calcareous rocks. As a rule it appears to be a lowland plant, but ascends to 300 metres. The plant belongs to the group with narrow leaves, usually more than twice as long as broado The stem is simple or branched below. The leaves are without hairs, or have few, very small, bristles. The stem-leaves are lance-shaped, 2-5 times as long as broad. They are very acute with 4-6 distant, long, spreading, awned teeth. The spike finally is much lengthened. The flowers are white or bluish-purple or violet. The bracts are ovate to lance-shaped, with 4-10 (usually 6) teeth, similar. The calyx is devoid of hairs, or has a few very small bristles, with triangular to lance-shaped teeth. The corolla is small, the lobes of the upper lip turned back, notched, or with a few small teeth. The capsule is wedge-shaped to long, blunt to notched, without hairs, or slightly hairy above.