There are many members of the speedwell family. Some are annuals, and some, such as thyme-leaf, are hardy perennials. All are low-growing, ground-hugging plants, and remain particularly difficult to control. Thyme-leaf speedwell is a dark, shiny green. Its egg-shaped leaves are opposite each other and closely spaced on creeping stems. It forms dense, spreading patches that suffocate good turf. Flowers are white, tinged with purple, and have four irregularly shaped petals. Other species of speedwell have flowers that range from bright blue to purple. A most unique characteristic of this family is the heart-shaped seed capsules. They contain many seeds and are arranged along the stem below the flowers.