By far the most wide ranging Cypripedium in all of North America is C. parviflorum v. pubescens, also known as the large yellow lady slipper. It has been found in 42 of the lower 48 states in the US plus Alaska (missing only in California, Florida, Louisiana, Nevada, Oklahoma, and Oregon), as well as all of Canada’s 10 provinces and two out of three territories (missing only in Nunavut). This plant is wide ranging not only in physical space, but in appearance as well. Plants in the far north sometimes stand little more than hand high and bear dwarfed flowers with nearly perfectly flat petals, while those found in the rich forests of the southern Appalachian mountains can grow taller than an adult man’s knee and have flowers nearly as big as the same man’s hand if splayed out. Due to this extreme range across geographic space and habit it has been the most problematic North American Cypripedium to delineate into a clean category. This is compounded by its interaction and interbreeding with v. parviflorum, and where their ranges overlap, the separate species, C. candidum.
Cypripedium parviflorum v. pubescens (hereafter referred to as v. pubescens) is a large deciduous, perennial, terrestrial orchid most commonly found in moist forests. Depending on where the plant is found growing, its height can vary widely, with flowering specimens standing little more than 12 cm tall and as much as 80 cm, nearly rivaling C. reginae in stature. Growth stems bear between 3-6 pubescent, ovate to ovate-lanceolate leaves, deeply ribbed, with each 6-20 cm long and 2-10 cm wide, and borne alternately off the stem. The vigorous root stock is like other Cypripedium species with a creeping, branched rhizome bearing numerous, creamy white to amber yellow non-forking roots that can exceed 40 cm in large specimens. In nature this plant can grow a single stem or be large clump numbering 20 or more stems, however plants with 3-5 stems is closer to the norm.
Flowers are borne at the top of the stem, usually singly, but occasionally in pairs. As its common name implies, they tend to be rather large with a natural spread up to at least 12 cm in larger flower forms, however the form planipetalum of the far north can be half that size. The dorsal sepal is large and broad, up to 8.5 cm long and half as wide, with a tendency to stand more or less erect, but sometimes overhanging the lip as in C. kentuckiense. It can be twisted at its end much like the petals, or be nearly perfectly flat depending on the plant. The synsepal is a bit smaller, and though it is held just off the lip’s surface, it curves to follow its contour. The petals are long and narrow, and again, depending on the form can vary widely in length, being as short as just 3 cm or as long as 9 cm, but rarely more than 1 cm wide. They tend to be presented at an angle of 45 degrees to the ground, but can hang lower. In most forms they are highly twisted, reminiscent of a spiral ribbon, though this can vary widely from plant to plant with some having extreme twisting and others much less. In the form planipetalum the petals tend to be presented almost at a perfect 90 degrees relative to the ground and have little or no twisting. The lip is large, up to 5 cm long, and tends to be ellipsoidal in shape, however some plants have more rounded lips. The staminode is triangular in shape with rounded corners and is held tightly over the column underneath.
Given its great range in flower form and size, it shouldn’t be surprising that v. pubescens is also variable in flower color. The most consistent colored part is of course the yellow lip, which, regardless of the population sampled seems always to be a deep lemon yellow. Unlike v. parviflorum, it rarely shows any red spotting on the outer surface or around its orifice, but it can have a few red splotches on the inner surface. The petals, dorsal sepal, and synsepal all have a base color of light green that is finely striated with varying amounts of chocolate brown. The degree of striation is what gives this species so much variety – it can be nearly absent in some clones and almost solid in others. The resulting visual impression is either a very pale flower to ones that look more reminiscent of v. parviflorum, so much so that you can confuse the two varieties easily. Some plants of the form planipetalum can have flower parts that are totally green or even with a yellow cast – an unusual look indeed. The staminode is always a lemon yellow color and usually has at least some red spotting on it. The flower’s scent is “floral”, but with no hint of sweetness.
Variety pubescens has the largest geographic distribution of any North American Cypripedium with the exception of C. guttatum which grows well into north central Asia. As stated at the onset, it can be found across much of North America, perhaps even as far north as the arctic circle and southward to nearly the Mexican border in the west and Florida in the east. Historically v. pubescens has been found in a wide range of habitats, from calcareous swamps in the northern US and southern Canada, to rich woodlands of the southern Appalachian Mountains, in high altitude coniferous forests in the desert southwest, to treeless limestone barrens in Newfoundland, in remnant tall grass prairies of America’s central states, and on talus slopes in the Rocky Mountains. For this reason, is very hard to generalize about this species’ habitat – suffice it to say it is broad. Perhaps the most novel place it has ever been found was in Bailey County, in the panhandle of Texas. A single plant was found there in 1929 by B.C. Tharp growing in a wet depression between sand dunes. No other plant was ever found in that area, however neighboring populations can yet be seen in the mountains of New Mexico and Arizona – a place where they are literally growing on the edge. Though widely distributed, this variety is in general decline due to any number of factors including collecting pressure, habitat loss or modification, climate change, and herbivory by ungulates, notably white tailed deer and moose. Still, sizable populations exist in parts of western Canada, the Great Lakes Region, and locally throughout the Appalachian Mountains. Monitoring and assessing such a wide ranging species is difficult except in places where it is extremely rare, for example Arizona (status – critically imperiled).
Cypripedium species in general, and this plant in particular, have been used historically as a folk remedy for ailments ranging from nervous conditions, headaches, fevers, stomach disorders, epileptic fits, insomnia, the DTs, muscle crams and spasms, and even as a hallucinogen if taken in large doses. The typical method of extraction is through boiling the root stock in water with the resulting infusion taken immediately, though homeopathic alcohol based tinctures are also made, and can be purchased to this day. The calming effect of this herb has given it the name American Valerian. Of course such practices also put wild populations at risk from collection since growing nursery stock is time consuming, expensive, and not an undertaking for the novice gardener. Would be buyers should also be aware that there likely are many bogus products on the market claiming to be Cypripedium extract, while in truth some other cheaply available herb was used in preparation instead. Use your own judgement and ethics in making such purchases.
My first introduction to the large yellow lady slipper was my family’s garden in southern New York when I was just a young boy. Soon after purchasing the one and half acre wooded lot (and house) I grew up in, my father began clearing out the scrubby underbrush that dominated it, and planted a wide array of exotic and native plants. One of his first purchases were three types of “slipper orchid” from a nursery in Vermont – likely C. parviflorum v. pubescens, C. acaule, and C. reginae – three of each. He planted them out directly into the acidic, rocky woods loam native to the area and within a short time only one plant was left – a single growth of v. pubescens. There it grew for the next 18 years, never getting any bigger or smaller, but never missing a year of flowering either. I relished in its beauty each spring and hoped to find it somewhere in the local woods one day. Despite near heroic efforts, my dad and I never located even a single specimen, though we heard tales of them growing here and there all around us. To put this into perspective, this species was once found in Queens County, N.Y.C., and to this day county-level distribution maps for the state still record it as being present. I wish you good luck in your search in finding any there now!
My next encounter with v. pubescens was in the mountains of the southern Appalachians a decade later. Here I found it growing near wet seeps in deep deciduous woods, on the steep slopes of rich cove forests, as well as on relatively dry ridge lines at fairly high altitudes – up to 1500 meters in places. Plants in this region were highly variable in color – some with very pale flowers and others with such dark and twisted petals I first mistook them as v. parviflorum.
On all my journeys across the Appalachians, from northernmost Georgia clear up to north central Maine, I have never seen a truly massive colony. I do remember one mountaintop in Great Smoky National Park that was covered with a scattered colony that must have numbered into the many hundreds of plants spread out along a two mile long ridge line. The vast colonies of the Great Lakes Region are legend, and in truth, these days most of those populations are probably just that, legends. Like its cousin C. reginae, the fabled colonies of yesteryear are mostly a thing of the past. For a comprehensive report on this variety check out this excellent conservation assessment pdf.
For much of the mid 20th century all C. parviflorum varieties were included under the Eurasian species C. calceolus. Early authors described v. pubescens under a host of names, including C. calceolus (Linnaeus, 1753), C. flavescens (Redoute, 1802), C. pubescens (Willdenow, 1804), C. luteum (Rafinesque,1828), C. assurgens, C. aureum, C. furcatum, C. undatum (all Rafinesque, 1833), C. veganum (Cockerell and Barker, 1901), and C. bulbosum v. flavescens (Willdenow, 1913). Discussion began to brew again in the mid 1980’s and finally by the mid 90s (largely under the work of Sheviak and Atwood) a new picture began to form with v. parviflorum, v. pubescens, and v. makasin (a name resurrected by Sheviak, and still disputed by many, who put it under v. parviflorum) generally being accepted as true varieties of Cypripedium parviflorum, while C. kentuckiense was raised to specific rank. The enigmatic v. planipetalum (Fernald, 1940) is now largely considered an ecotype of v. pubescens and this conclusion has been supported by allozyme studies (Case, 1993).
This latter plant is a fascinating denizen of limestone barrens in the eastern end of its range in Newfoundland, Quebec, and Ontario, and also at home on treeless talus slopes in the high mountains of the Rockies from Colorado to Alberta. Looking at the plant you cannot help but see that it is dwarf in stature and that the petals are truly held flat or are just slightly twisted (hence the name planipetalum – literally “flat-petaled”). This plant has been recognized as a separate taxon, as a variety of v. pubescens, and most recently merely an extreme ecotype of v. pubescens. Being a plant of extreme environments – cold, windy, and treeless – some have argued that environmental conditions, not genetics, give the plant its distinctive form. Sheviak and others have tested this theory by growing “v. planipetalum” under normal garden conditions and all eventually changed into normal looking plants over a few seasons. Sheviak, to push this point, went a step further. He grew a normal v. pubescens in a growth chamber that approximated the cold, exposed areas that the flat petaled plant lives. In a short time these plants became shorter and their petals less twisted, thus adding proof to his theory.
Having said that, I know of at least two cases where this hasn’t happened. Darcy Gunnlaugson on Vancouver Island has grown planipetalum type plants alongside v. pubescens and the former maintained its dwarf habit for years without “reverting”. I’ve heard similar reports from folks in Germany. So, in the end, who can be sure. Perhaps there really are dwarf genotypes that aren’t just a product of extreme environments. To further support this idea, in a number of places v. pubescens and the form planipetalum are growing very close to each other in nature, for example, on the famous Bruce Peninsula of Lake Huron.
Another form of v. pubescens that is noted from time to time in the literature are fabled “alba” forms, that is, plants with white lips and greenish petals, dorsal sepal and synsepal. Without a doubt these white flowered plants are not pure v. pubescens, but rather the natural hybrid between this plant and C. candidum, C. x favillianum. This is a lovely hybrid, very easy in the garden, with a lip color that starts out creamy yellow and matures into a bright ivory.
Which brings me finally to growing this admirable plant in the garden. The good news is that in most gardens this is the easiest Cypripedium species to keep growing and flowering year after year. The bad news is that it, like all Cyps, is not an easy garden subject – this is no Hosta. That aside, you can grow it in almost any well drained moderately acidic to mildly basic soil (~ pH range 5.0 to 7.5) and under “normal” garden conditions, preferably in light shade. It only requires moist soils that don’t get too droughty. Similarly, it is a plant of wide tolerance with regard to temperature, growing naturally from USDA zone 2 in the far north to zone 8 in the south.
If you want to grow this plant optimally however, I recommend a near neutral compost made up of mostly inorganic, gritty substrate – pumice, perlite or the like mixed with just a bit of organic material. As with C. reginae, this plant responds well to totally inorganic substrate rather than true soils, whether they be loamy or high in humus. The key is soil structure, open and airy being far better than tight soils with little air movement. That plant my father grew in New York for two decades was finally moved and put into a more airy mix and within a season had increased from one to three stems. Also, remember this is a plant of forests usually, so it benefits from high shade conditions, not full sun. In general, the more sun you give this plant, the more dwarf its habit. I remember plants growing at an arboretum that were under a canopy of deciduous trees until a storm knocked many down. The plants grew and flowered nicely the next spring, but since they were now in full midday sun, they only stood about hand high – certainly a novel appearance, but ultimately too stressful, especially in warmer summer areas. Clonal variation is high with this variety, but generally most will be best suited for USDA cold hardiness zones 3-6, with zones 2 and 8 being the extreme limits of their temperature tolerance.
If happy this plant can put on many stems over time – clumps of 20 or more stems flowering all at once are not unknown and quite a spectacle. Care needs to be taken of such large clumps however. Over time they tend to lose vigor, especially at the center of the clump, so if you see them flower less or get smaller, then dig the plant up in the fall and inspect the roots. If they seem healthy, you can replant the whole clump as is, but put it into new, fresh compost. To maintain large clumps it is likely you will have to replant them every several years, watching them closely. Of course large clumps can also be divided (again, in the fall after the leaves go down) and planted out separately. This actually revitalizes them provided divisions have adequate roots and rhizome. A division with 2-4 eyes and ample roots is an ideal size to grow on.
I have managed to grow this plant in southern Japan in an equivalent USDA zone 9, but just barely. It isn’t something I’d recommend, but if you are up for the challenge, give it a go. For more on my efforts, check out this article on growing Cyps in a hot climate. Be prepared for failures however.
Here’s another lovely Cyp to grow in the open garden, perhaps the best of all Cyripedium species. Luckily, many artificial hybrids now exist with this variety as one parent, including the large flowered C. Aki (v. pubescens x macranthos). So far it seems pretty easy in the garden and has good hybrid vigor. Again, avoid taking plants from the wild unless they are threatened with destruction. This plant is readily available from many vendors of rare woodland plants – yes, at a higher price, but you can rest better at night realizing you aren’t harming natural populations.