Indicator Species - A Closer Look

Indicator Species - A Closer Look

Small White Lady's-slipper (Cypripedium candidum)
An endangered species in Ontario
photos and text by P. Allen Woodliffe, MNR District Ecologist, Aylmer District
Bluestem Banner - Spring 2003

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Orchids have a particular appeal to naturalists. Endangered prairie orchids are especially esteemed.

Small White Lady’s-slipper is one of the most restricted orchids in Ontario and is currently found, in Canada, only in the provinces of Ontario and Manitoba. It has declined significantly from its original range, as has its prairie habitat, to the point that in Ontario it only occurs in Lambton, Norfolk and Hastings counties. In Norfolk County the population, when last checked, was down to a single plant in the Turkey Point area, and in Hastings County a very small population occurs in the Stoco Fen. Only the Lambton County populations, all on private lands where prairies are managed with regular fire, are considered healthy. In fact of the several sites where they occur, it is not uncommon to see dozens or even hundreds of these delicate plants swaying gently in the spring breezes.

Shortly after the spring fire season, the stem and leaves of this long-lived perennial begin to emerge above the ash covered ground in early May. Sometimes a dozen or more stems will arise from a single rhizome, reaching heights of 36 cm, although 20-25 cm is more typical. The three or four erect leaves are obviously folded at the mid vein. Above the leaves at the top of the stem is a single, small flower, a bright white inflated pouch about 2.5 cm in length, resembling that of a slipper. The genus Cypripedium comes from an incorrect interpretation of Greek words meaning ‘Venus’s shoe’, and the species name candidum means ‘white’.

This pouch is sometimes finely veined or spotted with purple around the opening in the top, with heavier spotting visible inside. The ‘slipper’ is actually a modified petal. There are two other petals, occurring as twisted, greenish-yellow parts extending laterally on either side of the pouch. Often they are slightly tinged with brown or purple. Three similarly coloured sepals are also present, one extending upwards above the pouch and the other two extending downwards. In southern Ontario, Small White Lady’s-slipper flowers from about mid-May until early June.

The Small White Lady’s-slipper is pollinated by insects, often small bees. Because this plant blooms early in spring, cool weather often hinders insect activity and therefore pollination. Also, late spring frost or fire can prevent proper flower development and so typically only a small number of flowers produce seed. Orchid seeds are very numerous, usually thousands per seed capsule, but small and very light, relying on wind dispersal. Germination is usually quite low.

Sometimes occurring in the same location as the Small White Lady’s-slipper is the much more common and widespread Small Yellow Lady’s-slipper (Cypripedium parviflorum). The latter species typically flowers a bit later in the season, but where they occur in close proximity to the former, and if the flowering period overlaps, interesting hybrids can occur. Depending on the genetic lineage, various combinations of white slippers, pale yellow slippers, greenish sepals or very purplish sepals will occur. These hybrids are actually much rarer than the Small White- Lady’s-slipper and it is always a delight when searching for and finding this endangered species to discover what colour combinations exist in a population.

Most prairie plants benefit from the regular occurrence of fire, and the Small White Lady’s- slipper is no exception. Obviously the main threat to this species would be conversion from prairie to agriculture, urban development or some other unnatural land use. However even restricting the use of fire, which results in vegetation succession to more shaded, shrubby conditions is also a factor in its decline. If fire is resumed as a land management practice, the species can usually regain its position in the natural landscape. Disturbances such as foot or vehicular traffic can also cause decline.

Small White Lady’s-slipper, as well as the other Cypripediums, have been considered sedative, antispasmodic medicines. Pioneers used the powdered root to treat insomnia.

Are there opportunities for the Small White Lady’s- slipper to be discovered in new places in Ontario? With the resurgent interest in prairie protection and management, plus the effort going on to discover new remnants, there is always hope. But the likelihood of finding high quality wet-mesic prairie habitat required by this species will probably be very small. If the species didn’t occur there in the first place, the chances of new seeds finding these sites are probably as miniscule as the seeds themselves.