There are two varieties of what is called the Greater Yellow Lady's-slipper and they are similar in character. The second variety - Cypripedium parviflorum Salisb. var. makasin has smaller flowers and much less hair, but in Minnesota, it has a similar range.
For var. pubescens:
The flower stems can be 8 to 30 inches high and are hairy.
Leaves up to 6 inches long, are ovate and have prominent parallel veins and a base that mostly surrounds (clasps) the stem; leaf margins are smooth but the surface is hairy. Both stem and leaves of the Cypripedium genus can cause dermatitis.
Flowers: Members of the genus Cypripedium have three petals and three sepals. These are the same color which can range from yellow-green to purple-brown in this species. Two sepals are joined together as to appear as one, forming the lower sepal. This joined sepal and the upper sepal form a lower and upper hood. Two petals are usually horizontal or descending, usually spirally twisted and usually purple-brown in color. The lower third petal forms an inflated lip, or pouch, or slipper, which is yellow, sometimes with purple veining and with some reddish brown dots on the inside. The larger yellow variety has flowers from 2 to 3 1/8 inches long and a pouch 1-1/8 to 2 inches long while the smaller variety (var. makasin) has a flower that is 1 to 2 inches long with the yellow pouch from 3/4 to 1 1/8 inches long and the sepals and petals are of darker color. The pouches of both varieties may show purple veins. There is usually one but may be two flowers on an inflorescence. Behind the flower stem is a green bract, resembling the leaves but smaller. The sexual parts are inside the pouch, somewhat hidden by a the large ovoid dorsal anther of a false stamen (a staminode). There is a real anther to either side.
Seed: Pollination is usually by bees and fertile flowers produce an oblong-ellipsoid ribbed capsule containing many small dust-like seeds, but reproduction is normally via the root system. The capsule ribs have short hairs.
Habitat: This Cypripedium is widely distributed due to it acceptance of sandy to loamy soils and moisture conditions ranging from moist to slightly dry. The root system is rhizomatous. Partial sun is preferred. From the wild they do not transplant with complete success due to a symbiotic relationship with certain soil fungus called “mycorrhiza.” The nursery trade has learned to grow them commercially.
Names: The former scientific name for this species was Cypripedium calceolus var. pubescens, but that is no longer accepted. The genus Cypripedium is derived from several Greek words that mean "Venus's shoe". The species name, parviflorum, is from the Latin meaning "small flower". The variety name pubescens means 'downy' referring to leaf and stem surface. The author names for the accepted plant classification are as follows: For the species itself ‘Salisb.’ refers to Richard Anthony Salisbury, (1761-1829), British botanist who developed an extensive garden and published many taxonomic revisions, but much of his work was plagiarized and discredited, however some of his work has been recognized as is the case here. As to the variety - first to publish was ‘Willd.’ who was Carl Ludwig Willdenow (1765-1812), German botanist, a founder of the study of the geographic distribution of plants. He was director and curator of the Botanic Garden of Berlin. His work was amended by ‘Knight’ who was Joseph Knight (1778-1855) English horticulturist whose most famous publication was the 1809 On the Cultivation of the plants belonging to the natural order of Proteeae, except that it contained other work on other families submitted by Richard Salisbury (yes, the same) who had plagiarized it from Robert Brown.
Comparisons: Greater Yellow Lady's-slipper is one of the two Lady's-slippers in the Garden (the other being the Showy Lady's-slipper), the Yellow blooms first, usually by mid-May but if the season is late, it could be the end of the month. There are several clumps, the largest near the patio area.
Varieties: There are three varieties of C. parviflorum. The variety "pubescens" (which means 'downy') is used to designate the larger flowered variety with its hairy stems, bract and leaves, compared to variety makasin, (Cypripedium parviflorum Salisb. var. makasin), which has smaller flowers and only sparse hair on the bract when young, and which grows in swamps and bogs and was formerly present in the Garden (see historic photo below). The larger flowered variety can occur more often on upland sites, which is where it is situated in the Garden. The third variety, var. parviflorum is also small flowered, with less hair but has much more densely spotted or blotched sepals and petals and is more restricted in range into areas that are south and east of Minnesota, Iowa and Wisconsin. According to Flora of North America (Ref.#W7) only this variety should be called "Lesser Yellow Lady's-slipper".
Below: For comparison - an example of the two varieties of Greater Yellow Lady's-slipper. 1st photo is of var. pubescens, 2nd photo is of var. makasin. Note the coloration and development, including the hairy stem and the green bract behind the flower are much the same as the larger variety - only the darker color of the purple-brown parts and the size is different.
Below: 1st photo - Two sepals are fused together to form the lower one and the third sepal forms the upper hood. The laterals are twisted petals and the pouch is the third petal. 2nd photo - A flower beginning to unfold, note the unfolding green bract behind the flower head. You can also see that the upper and lower sepals are the closest elements to the flower stalk.
Below: Fertile flowers form an oblong-ellipsoid ribbed seed capsule containing many small dust-like seeds.
Notes: Eloise Butler's records show that she obtained plants of this species as early as 1907 from within Glenwood Park (Now called Theodore Wirth Park); then in 1907 and 1908 from a source in Mahtomedi, MN; in 1908 from Osceola, WI. In 1911 and 1914 she gathered plants from the Big Bog area of Lake Minnetonka; there were several plantings in 1912, on May 22nd from Mound MN and on June 12 from Washburn Park, Minneapolis. Also, on June 18, 1916 ("2 clumps large") from 6th Ave. North in Minneapolis, more from there in 1919; "three large " on June 10, 1917 along Superior Blvd. in Minneapolis. MOre plants in 1919 and 1920. Other records indicate specimens of this plant were acquired from Mahtomedi, MN; from the Glenwood Park Bog, Minneapolis; from Fridley, from Twin Lakes, and from a meadow at Savage, MN. More were planted in 1920. Curator Martha Crone also planted the species many times, every year in the 1930s starting in 1934, and more introductions in '41, '49, '54, and '56.
The species is not long lived in a transplant environment as this indicates. From reports published in The Fringed Gentian™ we learn that poor rainfall in the late 1980s led to no bloom on the plants in 1988 and 1989. They finally bloomed again on May 23 1990 and then died out. In 1991 Gardener Cary George reported that the plants had disappeared. Fortunately, Friends member Judy Jones donated a large clump from her mother's garden. Cary divided it and planted one clump on the path to the front gate and another just of the patio area near Guidebook station 8. That is apparently, the clump that still blooms there. Cypripediums are difficult to grow via transplanting as explained in the article below.
For an article on both Lady's-slippers in the Garden and some history see Orchids in the Garden by Cary George in the Archive - Educational section.
Greater Yellow Lady's-slipper is widely distributed and found throughout much of North America with the exceptions being several states in the far south, several states of the far west and the Canadian Provinces of Yukon and Nunavut. In Minnesota both varieties are mostly found in the "old woods" band north and east of a diagonal line from Blue Earth County in the SE to Clay county in the NW. This is much of the state with the exception of drier SW quadrant. However var. makasin has more exception to that rule.
There are six Cypripediums found in Minnesota: C. reginae, Showy Lady-s-slipper; C. acaule, Stem-less Lady-slipper (or Moccasin flower); C x andrewsii, Andrews's Lady-slipper; C. arietinum, Ram's head Lady-slipper; C. candidum, White Lady's-slipper; and C. parviflorum, Greater Yellow Lady's-slipper in two varieties - var. makasin and var. pubescens.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"