The Yellow Lady's Slipper Orchid - Cypripedium calceolus

Aquilegia Vol. 2, No. 1 January - February 1978

Cypripedium calceolus, by William A. Weber

One of the really endangered species in the Colorado Flora, but unfortunately not eligible for the Federal Protected list because it happens to grow in other parts of the world, is the Yellow Lady’s Slipper orchid. Cypripedium calceolus L. It is so well-known that no description or drawing is necessary here. In fact, recognition is not the purpose of this article. Many of the known colonies of this orchid are on private land and they have been protected by the landowners for many years. Those few colonies still present on public lands might best be left unpublicized if they are to survive. Certainly, the Yellow Lady’s Slipper should never be collected, picked, or taken into the garden any more if it is to continue to survive in the wild state in Colorado.

a photo of a yellow lady's slipper plant

Yellow Lady’s Slipper (Cypripedium parviflorum var. pubescens)

 J. D. Lovis, writing in The Naturalist, pp. 5557, 1976, discusses the problems of conservation of this orchid (another subspecies of C. calceolus) in England, where there is only one known remaining small colony as well-protected as it can be,”yet in real danger of extinction for other reasons. Lovi s writes: “There is no doubt that the population of Cypripedium calceolus in this country is now far below a viable minimal level. This means that unless it can be assisted to increase its population size, it will certainly become extinct from natural causes, even if the hand of man does not (as past experience makes only too likely) first apply the coup de grace.

Unlike Ophrys apifera (Bee Orchid), C. calceolus is not adapted for self-pollination. Isolated plants have no chance of being pollinated, simply because of the lack of a pollen source. Even where two or three flowers occur in proximity, the chance of pollination is low. Like other orchids, Cypripedium pollen is transferred in sticky masses – an all-or-nothing tactic. The likelihood of seed being set naturally in this country is therefore very remote.”

Lovis goes on to point out that climatic fluctuations sometimes encourage, sometimes discourage flower production as well as vegetative performance. Inevitably for small populations, the net results are usually decrease and extinction. Slugs damage the plants, and while seeds in a single capsule are astronomically numerous, it is often 6 to 10

years before a seedling can be noticed in the field. In the English colony. it is certain that the entire “last population” is a clone, so that the plants are all genetically identical and unable to “cross”-po1linate. since they are mostly self-incompatible, and although seeds are sometimes set, these have never germinated. A lot of study has gone into trying to develop germination, but at the moment it appears that the only practical solution is to find another population and artificially cross the plants.

Young plants of Cypripedium can be mistaken for lots of other broad-leaved monocots, and rumors have been rife that there are, indeed, other colonies of Lady-Slipper in England, but all leads have checked out negatively. Now the problem is, in England’s conservation-minded public, there just might be a colony of Cypripedium somewhere and it is being kept secret. As long as the plants do not flower the secret can be easily kept, but once in flower someone, possibly unscrupulous, will learn about it, and the curtain falls on the population. So the Nature Conservancy Council is in the position of having to beg the people not to sit on these colonies in silence, but to inform the Council so that cross-pollination programs can be put in effect, and the Council must go out of its way to assert its moral character in the matter.

The last sentence of Lovis’ article is telling.”Anyone who is in possession of knowledge of a second colony and does not now inform the Nature Conservancy Council should realize that they will have contributed towards, and must bear some of the responsibility for, the ultimate disappearance of this species from Britain just as effectively as if they had cut the flower and put it in a vase or a plant press, since they will have just as certainly deprived the plant of the opportunity of setting seed, which is the only way in which it may be saved.”

a photo of yellow lady's slipper

Yellow Lady’s Slipper (Cypripedium parviflorum var. pubescens)

It is very likely that the Colorado populations, small as they are, are going the way of the British colonies and ultimately survival will depend on the same measures.

Editor’s note: The name of Cypripedium calceolus has since been changed. In William Weber’s last Colorado Flora, published in 2012, he named it Cypripedium parviflorum. Jennifer Ackerfield, in her Flora of Colorado calls it Cypripedium parviflorum var. pubescens, and the Colorado Natural Heritage Program calls it Cypripedium calceolus ssp. parviflorum.

Globally, Cypripedium parviflorum is still considered secure, but in Colorado, the Colorado Natural Heritage Program tracks 28 populations and lists the species as S2 (Imperiled). In England Cypripedium calceolus is still called Cypripedium calceolus and there is still one remaining population which is under guard in a secret location.