Native to Europe, these creeping perennials spread by surface and underground runners to form low, dense foliage mats. Upright spikes of hooded flowers rise above the leaves in summer. Though names are much con- fused, all species are tough, tolerant, and deep rooted. They are useful for small-scale ground covers and can endure the occasional footstep; set 1 ft. apart. Choose location carefully, though: These plants are too invasive to risk near choice, delicate rock garden plants. After bloom, shear off spent flower spikes to keep the planting neat and prevent seed formation.
P. grandiflora. Leaves to 4 in. long; stems to 1 ft. tall, bearing spikes of 1- to 1-in., purple blossoms. Varieties include 'Blue Loveliness', 'Freelander Blue' (compact grower with violet-blue blooms over a long period), 'Pink Loveliness', 'Purple Loveliness' (lilac-purple touched with white), and 'White Loveliness'. Hybrid 'Summer Daze' is compact, at 10 in. high and wide, with rich pink flowers.
P. vulgaris. This is the common species. Smaller in all its parts than P. grandiflora, with leaves to 2 in. long, 1-ft. stems, and purple or pink flowers just in. long. P. v. incisa has deeply cut leaves.