The genus Clematis consists of over 280 species of climbing and woody herbaceous species, mostly deciduous, but some evergreen. Whilst they are spread widely over the temperate regions of the world, they mostly grow in the Northern Hemisphere.
The genus belongs to the family Ranunculaceae, along with such other varied genera as Aquilegia, Delphinium and Thalictrum. While it is difficult to see the similarity between those genera and Clematis, other members of the family will bring similarities to mind, such as Ranunculus (the buttercups) and Caltha (the king cups).
The two characteristics mostly associated with clematis are their habit of climbing (though by no means all species do so) and their beautiful flowers. Climbing is achieved by specially adapted petioles (leaf stalks) which wrap around suitable supports. If such supports are not available, they will not climb, say, a wall, but grow as a tangled mass or out along the ground. The ability to climb gives the genus its name, which is derived from the Greek klema, a vine-branch or twig.
The flowers do not carry true petals, carrying instead a group of 4 to 8 petal-like (petaloid) sepals (often referred to as tepals). In shape, the flowers are normally either a flat disk or bell shaped (campanulate), though other shapes, such as tubular, do occur. Flowers are normally bisexual, though some species have single sex flowers. They are normally solitary or in panicles.
Another important characteristic is the seed heads. Most species carry seed heads which become very attractive as they develop into fluffy balls as the seeds ripen. The seeds themselves are small, inconspicuous achenes.