Plant 387

Cypripedium species (Orchidaceae)

Lady’s slipper orchid

Cypripedium species belong to what some consider the largest plant family, the orchids. The genus, with approximately 50 species, is commonly known as the lady’s slipper orchids, an allusion to the resemblance of the characteristic balloon-like lip of the flower to a slipper. Only one species, Cypripedium calceolus, grows in Britain, which is now found in only one secret location in Yorkshire, where it is protected during the growing season. However, Cypripedium calceolus is not uncommon in other parts of Europe. The species’ British distribution was reduced by past over-collection, clearance of their preferred habitat of light woodland on moist calcareous soils and by sheep grazing.

Cypripedium species are found growing in temperate and subalpine regions, in the northern hemisphere extending through Mexico into Central America. Most species grow in colonies, some of which can cover large areas, e.g., Cypripedium micranthos and Cypripedium tibeticum. They are deciduous, terrestrial perennials with fleshy rhizomes that store food during dormancy. The plants also spread by means of these rhizomes, giving rise to colonies of cypripediums with the same genetic make-up, and by seed. Orchids have very fine seed which has very little in terms of food reserves, thus a lot of seed is produced to increase its chances of finding suitable growing conditions. Cypripedium growth starts in the spring as temperatures rise and moisture levels increase. Flowering for most cypripediums occurs from May to early July, but a few species, such as Cypripedium irapeanum and Cypripedium molle, will flower in August.

Cypripediums are usually pollinated by bees, although a few species are pollinated by flies. They are attracted to the visual appearance of the flowers and well as by scent. The insect tries to land on the rim of the flower lip, only to find itself falling inside down the slippery inner surface. The only way out is by using the hairs at the back of the lip which act as an escape ladder. These take the insect past the fertile anthers where the sticky surfaces of the pollinia (a mass of pollen grains) become attached to the insect. Pollination is achieved when the insect visits another flower and falls into the same trap and must crawl out past the stigmatic surface, where the pollinia is left behind and pollen germinates.

In recent years, cypripediums have attracted increased horticultural interest as numerous hybrids have been bred that are well suited to garden cultivation.

Cribb, P 1997. The genus Cypripedium. Timber Press.

Kull T 1999. Cypripedium calceolus L. Journal of Ecology 87: 913-924.

Li P et al. 2006. Deceptive pollination of the Lady's Slipper Cypripedium tibeticum (Orchidaceae). Plant Systematics and Evolution 262: 53-63.

Lucinda Lachelin