There are a surprisingly small number of ivy species, 19,but taking English Ivy (H. Helix), on its own, it has over 400 cultivated forms. Evergreen climbers, enjoying most situations and soils, easy to prune, quick growing up walls, trees, or covering the ground. Flowers small, in umbels, some late in the year.
Ivies, especially the native species H. helix and H. hibernica, are perhaps THE most important plants for wildlife in Britain. Any that climb provide nesting, roosting and hibernation sites for birds (robins, wrens, house sparrows etc) and insects (brimstone and bomma butterflies); the flower buds are the main larval food for holly blue butterflies; the autumn flowers are a magnet for late insects such as wasps, hornets, butterflies, moths by night, bumblebees, hoverflies, ivy bees - in fact anything that eats nectar or pollen; the berries are the last food to ripen in late winter and essential for keeping birds alive in the event of a February 'Beast from the East', from pigeons to blackbirds and blackcaps. And it is NOT a parasite - it does not kill trees. Neither does it destroy brickwork - it actually protects especially older bricks against the damaging effects of frost - although you may want to keep it from reaching your soffits! Those forms that do not flower are still of value structurally, and even the ground-cover forms provide shelter for invertebrates and amphibians: to encourage flowering, allowing upward growth into sunlight is recommended.