A bright lady slipper in a dark forest

By Jeff Mitton

More than 20,000 species of orchids have been described, and more species are being discovered each year.

Most orchids are tropical epiphytes, or plants growing on other plants. Temperate orchids are terrestrial, rooted firmly in the ground. More than two dozen species of orchids are native to Colorado.

Calypso bulbosa is known by several common names: lady slipper, fairy slipper, Calypso orchid. It is circumboreal and is found today in Sweden and Finland, eastern Siberia, Japan, Canada and most of the northern and western states. Although it is widespread, it is rare and frequently occurs as a solitary plant in a pine forest, usually on north-facing slopes. But occasionally lady slippers grow in small, dense populations.

Lady slipper is a small plant. It has a single oval leaf growing from the ground and a single stalk rising 2 to 9 inches. Each stalk has a single flower. The flower is bilaterally symmetric and is composed of three petals and three sepals. The lower, central petal is modified to a pouch, inspiring the notion of a slipper. The sepals and two upper petals are lavender. The outer portion of the slipper, called the lip, is white with three prominent stripes of bright yellow hairs. The inside of the slipper is white with dark purple dots and stripes. Beneath the lip is a white, forked structure that looks like a pair of nectaries, but they do not produce any secretions.

Stalks and flowers appear in late spring or early summer. The orchid grows from a bulb-like corm; each summer the old corm grows a new bulb with two fibrous roots and a stalk with a single leaf. The leaf overwinters and nourishes the flowering stalk that appears the following spring. Lady slippers live up to five years.

Lady slippers indulge in deceptive pollination. Their bright flowers attract bumblebees, but they do not produce nectar. Bumblebees visit flowers primarily to collect nectar. If a flower has been drained of nectar, they move on to the next flower, but if they are not rewarded they switch to another species. Young, naive bumblebees will visit lady slippers and inadvertently transfer pollen, but after visiting a few flowers they learn their lesson and will not return to lady slippers.

Deceptive pollination is a risky strategy, for if the pollinator learns its lesson quickly, flowers will not be pollinated. But if flowers can get by with only the brief services of naive pollinators, they have conserved energy by not producing nectar. So, are lady slippers deceptive and deceitful, or thrifty?

Fortunately for lady slippers, a single pollination is sufficient to produce thousands of tiny seeds. The tiny seeds rely on a mutually beneficial relationship with fungi for germination. Microrrhizal fungi help the seed garner water and minerals from the soil, and in return they receive nutrients after the orchid begins photosynthesis.

But orchids are very fussy when it comes to microrrhizae, and if the correct species are not available, the seeds will not germinate. Similarly, if an orchid is taken from its native site and transplanted to a place lacking the required species of microrrhizae, the orchid withers and dies. Because transplantation almost always fails, it is far better to enjoy orchids where they grow naturally.

Jeff Mitton, mitton@colorado.edu, is chairman of the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.