Glandularia rigida has rough, dark green leaves and vivid purple flowers in the spring and summer. If this plant starts to look ragged, just cut it back to the ground, and fresh growth will sprout from underground stems. Even in very cold winters, this plant bounces back from these rhizomes. The foliage feels like sandpaper. This is one of the largest verbenas, growing to 2 feet tall by 4 feet wide.