Description: This native perennial plant is 1–2½' tall and usually unbranched. The central stem is round in circumference, rather stout, and densely covered with hair. Three or more leaves alternate along this stem. These leaves are up to 6" long and 4" across. They are oval-ovate, smooth along the margins, and pubescent. Parallel veins are readily observable along the upper surface of each leaf. The base of each leaf clasps the stem. The color of the foliage can vary from dark green to yellowish green, depending on growing conditions and the maturity of the plant.
The central stem terminates in 1 or 2
flowers. Each flower is held above the foliage on a long stalk that has a
single leafy bract behind the flower. This bract resembles the leaves, but it
is smaller in size. Like other orchids, each flower has 3 petals and 3 sepals.
However, because two of these sepals are fused together, there appears to be
only 2 sepals. The lower petal is in the shape of a slipper or a pouch with an
opening on top; it is bright yellow, shiny, and 1¼–2" in length.
Within the interior of this petal, there are frequently reddish brown dots. The
2 lateral petals are narrow, more or less twisted, and 2–3¼" in
length. They vary in color from greenish yellow to brownish purple and have
fine veins running from the base of the flower to their tips. The sepals form
an upper hood and a lower hood. They are broader and shorter than the lateral
petals, otherwise their appearance is similar. The reproductive organs are
located toward the posterior of the slipper-like lower petal. The blooming
period occurs from late spring to early summer and lasts about 3 weeks. There
is usually no noticeable floral scent. If a flower is successfully pollinated
by insects (often this doesn't occur), it will form a sack of fine seeds; these
seeds are easily carried aloft by the wind. The root system consists of a tuft
of fleshy fibrous roots. When several plants occur together, they are often
vegetative offsets of the mother plant.
Cultivation: The preference is partial sun to light
shade, moist to slightly dry conditions, and a soil that consists of loam or
sandy loam. Young plants require the presence of the appropriate
endomycorrhizal fungus in the soil in order to flourish. Starting plants from
seed is the job of an expert, although it is possible to successfully
transplant large plants that have been grown in a greenhouse. This is one of
the easier orchids to maintain in a flower garden.
Range & Habitat: Yellow Lady's Slipper Orchid is
an uncommon plant that is widely scattered across Illinois (see
Distribution
Map). It is less common than formerly, but still persists in small colonies
at several sites. Habitats include mesic to dry deciduous woodlands, sandy
woodlands and savannas, thinly wooded bluffs along rivers, and shady areas of
bogs. The size of local populations can increase in response to fallen trees or
occasional wildfires, as this reduces excessive shade from woody vegetation.
Some authorities regard this orchid as a native variety of Cypripedium
calceolus, which occurs in Eurasia. Under this system of classification,
its scientific name is Cypripedium calceolus pubescens.
Faunal Associations: The showy flowers attract small
bees and various flies. Charles Robertson observed Ceratina spp. (Little
Carpenter bees) visiting the flowers, although he did not consider them to be
effective at pollination. Herman Müller observed Andrenid bees pollinating
the flowers of Cypripedium calceolus (a very similar orchid in Eurasia).
He also observed various flies visiting the flowers, but they were ineffective
at pollination. Müller claimed that the flowers occasionally produce small
amounts of nectar as a reward, but other authorities dispute this. White-Tailed
Deer readily consume the foliage of this and other orchids, and local
populations may require a deer-resistant fence for protection where these
animals are abundant.
Photographic Location: A thinly wooded bluff
in Vermillion County, Illinois.
Comments: This is one of the largest and most
attractive orchids in Illinois. It is more abundant than most species of
orchid, although by no means common. While the flowers are in bloom, it is easy
to identify this plant as a Cypripedium sp. (Lady's Slipper Orchid)
because of the slipper-like lower petals. The only other species that it can be
confused with, Cypripedium parviflorum (Small Yellow Lady's Slipper
Orchid), has similar flowers that are smaller in size. The lateral petals of
its flowers are less than 2" long, while the slipper-like lower petal is about
¾–1¼" in length. The flowers of this species are more likely
to be fragrant. The Small Yellow Lady's Slipper Orchid usually has a pair of
leaves toward the base of the central stem, while Yellow Lady's Slipper Orchid
usually has 3-6 leaves along the central stem. When this latter orchid is not
in flower, it can superficially resemble Polygonatum commutatum
(Solomon's Seal) and similar species in the Lily family. However, the central
stem of this orchid and the upper surface of its leaves are pubescent, while
the latter group of plants has stems and upper leaf surfaces that are waxy and
glabrous.