This session, we are discussing the charming lady's-slippers or Cypripediums. I have been studying Cypripediums for about 20 years. Some of my investigations are into the behavior of populations from year to year but we have also looked at pollination biology, seed and pollen parent competence, flower longevity and species distribution. Over the past several weeks, we have been doing a census of the Showy Lady's-slipper orchid in a nearby park. It is difficult work finding plants but we have discovered 111 to date and over half of them flowered this summer-a very good sign. Furthermore, there was about 25% fruit set which tells us that pollinators are there and conditions were right this season for pollinator activity. Many seedlings are also a good indication that the population is healthy and we found many. Of course, being in a rather inaccessible part of a park does wonders for survival of these beautiful orchids. These orchids need space and time to grow.

Gaile
Marilyn, before we start, please explain how cyps differ from paphs and phrags.

MarilyninOttawa
I will be explaining the difference between Cyps and Paphs later on. Basically, Cyps have deciduous foliage and Paphs/Phrags do not. In Cyps, the dried flower adheres to the ovary whereas in the other genera, the flower falls when faded. That is the simplest explanation.

Cypripediums are mainly temperate terrestrial orchids of Asia, Europe and North America. China is the centre of generic diversity where, according the Cribb (1997) in 'The Genus Cypripedium', two-thirds of the 45 species have been observed. One of the most common in cultivation is the Formosan endemic C. formosanum. The leaves of this species are distinctively fan-shaped, appearing as if they had been sheared at the tips. Cribb considers C. formosanum distinct from C. japonicum although sometimes the names are confused. picture

About 25% of the genus is known from North America. Three species are reported from Mexico including closely related C. molle (left) and C. irapeanum (right). picture

Eleven other species are found in the continental United States; eight of these also being found in neighbouring Canada. These include the following:

Cypripedium acaule (Pink Lady's-slipper) A common species from eastern North America.

Cypripedium candidum (Small White Lady's-slipper) A threatened to endangered species in both the USA and Canada where agriculture has caused loss of populations. picture

Cypripedium passerinum (Sparrow's Egg Lady's-slipper) Mostly northern distribution. Self-pollinating.

Cypripedium montanum (Rocky Mountain Lady's-slipper) As the name implies, a Rocky Mountain species.

Chen Sing-Chi compared the orchid floras of temperate North America and Eastern Asia in a paper published in the Annals of the Missouri Botanical Garden 70: 713-723, 1983, where it was pointed out that more than two-thirds of the temperate North American genera have a phytogeographic link with eastern Asia orchid genera. Two Cypripedium species pairs are linked. The Ram's Head Lady's-slipper, C. arietinum is found in eastern North America and its Asian counterpart, Cyp. plectrochilum, is found in eastern Asia. Here we see the Ram's Head Lady's-slipper.

The Showy Lady's-slipper. C. reginae, has as an Asian counterpart, C. flavum. Here we see the white-flowered form of C. reginae. Some plants produce very pale pink flowers which under certain conditions appear white. An underexposed photograph will reveal if the flower has some pink coloration.

Molecular evidence supports the close relationships between Asian and North American taxa. What led to this disjunct distribution is not clear but it seems that these pairs and those of other orchid genera share a similar distribution.

Cypripediums are commonly know as 'slipper orchids' because of the characteristic slipper-shaped lip or pouch as seen here with the Small Yellow Lady's-slipper (Cypripedium parviflorum var. parviflorum). It is now accepted that C. parviflorum var. parviflorum is only found in the USA while another small-flowered var. makasin is found in wetland habitats in both Canada and the USA. picture

Cypripedium flowers have two anthers located on either side at the foot of the column and a sterile anther (staminode) which faces outwards partly blocking the pouch entrance as we see here in an opened flower of the Large Yellow Lady's-slipper, C. parviflorum var. pubescens. The staminode is yellow while the stigma is ivory. picture

The genus Cypripedium is temperate in distribution while its counterpart, Paphiopedilum, is tropical. Members of the genus Paphiopedilum have stiff leaves which are not deciduous whereas members of the genus Cypripedium have soft, plicate leaves. Paphiopedilum flowers separate from developing ovaries or detach from the ovary upon fading. After a Cypripedium flower is pollinated and has faded, it remains attached as a withered remnant to the developing ovary as seen here with C. californicum.

Cypripediums are long-lived rhizomatous deciduous perennials. They may exist singly or as clumps of stems connected by a stout rhizome. Roots are often long, hairy and fibrous. In the autumn, a perennating bud can be seen at the base of the present year's stem. The size of the bud is often a good indicator as to whether next year's shoot will bear flowers. picture

The roots are sometimes heavily infected with mycorrhizal fungi as seen here in a section through a root of C. acaule but the fungi may be actively growing only for part of the year. picture

Cypripediums may grow in acidic soil as with C. acaule or in calcareous soil as with C. parviflorum. There are species which prefer 'wet feet' including the Showy Lady's-slipper, C. reginae, which can be found in habitats that are seasonally flooded.

When there is insufficient rainfall, shoots of C. reginae may emerge late as seen to the left in this picture. The later emerging shoots are smaller and brighter green. They are unlikely to flower this season. picture

The European C. calceolus grow in drier conditions. Although it resembles the North American yellow-flowered lady's-slippers, it has been shown to be genetically distinct.

Some like the Stemless Lady's-slipper (C. acaule) and western North American C. fasciculatum have just two leaves nestled close to the ground but most others have three to eight-leaved stems bearing one to several flowers. Cypripedium fasciculatum bears its small clustered flowers close to the ground but after pollination, the flower stem elongates to hold the fruits high above the foliage. picture

N_Calif_Kathy
The better for the winds to spread the seed when the pod dehisces?

MarilyninOttawa
I expect so Kathy. I have measured breezes in local sites and it is surprising just how still it is close to the forest floor.

Cypripedium californicum bears many flowers, one in almost every leaf axil. I apologize but I only have pictures of the plant in fruit. The flowers are white and lemon-green/chartreuse. Exquisite! picture

Many Cypripedium species are spectacular in bloom with flowers lasting up to four weeks. We have observed that the large yellow lady's-slipper flowers last up to 23 days (Light & MacConaill, 2002). Flower longevity has been correlated with the cumulative minimum daily temperature. A majority of flowers faded when 140-150 degrees Celsius had been accumulated.

N_Calif_Kathy
You don't usually think of temps in terms of cumulative effect, do you?

MarilyninOttawa
Farmers think of cumulative daily maxima or heat units for the maturation of corn, for example. Here, we have a definite correlation with the cumulative minimum and after many years of study. It likely is a factor with other orchid bloom life but we do not have data.

The most widespread group in North America are the yellow-flowered lady's-slippers, Cypripedium parviflorum and its several varieties. This species is known from northern Ontario in Canada to Texas and from Newfoundland and Labrador in the east to Alaska and British Columbia in the west. Here we see the orchid growing in a Montana wetland. picture

Some very large flowered specimens of C.parviflorum var. pubescens are found growing in eastern deciduous forests. picture These large-flowered specimens have the 'wow' factor!

With such a wide distribution, geographical separation of members of the yellow-flowered group has given rise to forms that vary in plant characteristics and preferred habitat, and in flower size, colour, shape, scent, and pollinators. Variability in the yellow-flowered Cypripediums can be as great within as between populations.

The yellows require a minimum of three months cold annually to break dormancy. They prefer calcareous soil. Soil temperature should be cool but local populations regularly experience about 65F at their roots. Moisture should be available year-round.

Steve_in_the_Adirondacks
Marilyn, look at the first 4 pictures on this web site I made this site last summer. It shows how pale the Cyp. acaule are around here. I once saw hundreds of them along the French River in Ontario that were a deep rose color. The picture you showed tonight was far darker than our local version as well. Is it simply a genetic difference as I always assumed? I have wondered if soil or other conditions were a factor.

MarilyninOttawa
Steve, it looks to me that you have healthy vigorous plants with less than the usual complement of pink color. The color of C. acaule can vary quite a bit from pure alba to dark pink. As I understand it, the color varies according the number of alleles or copies of the gene coding for the anthocyanin pigment. The more the darker. Expression of the gene can also vary with temperature and likely, nutrition could play a role in overall color. I am looking forward to seeing a reputed population of pure white pouched forms next spring. Hope to have some pics to show then.

There are natural hybrids between species such as C. candidum and C. parviflorum var. pubescens and some of the these hybrids can be challenging to distinguish from the parental stock. Here we see two species which often grow together. Cypripedium candidum is on the left while C. parviflorum var. pubescens is on the right. Their hybrid flowers (C. Xandrewsii) can appear yellow through white. Look closely at the differences in the staminode shape. picture

Steve_in_the_Adirondacks
That reminds me... the ones I have seen in Canada grow in big clumps sometimes. Here, I never see even 2 next to each other. Always single plants.

MarilyninOttawa
We can get all kinds here Steve and I expect it may have to do with nutritional competence but there could well be other factors at work. The most we have locally are 3-4 shoots per clump. Many of the cyps are similarly variable in plant type.

Cypripediums attract pollinators but seem to offer no reward to flower visitors. Various native bees and bumblebees are frequently cited pollinators but hover flies and even beetles have been known to visit flowers. Here we see a native bee pollinator, Andrena sp., captured by a crab spider. The white fabric in the pouch has been used to block pollinator entry during pollination experiments. picture

N_Calif_Kathy
Ha! I looked at that picture several times and only now do I see the spider! Great mimicry!

MarilyninOttawa
Crab spiders can change their color and pattern to blend in with a flower. Misumenops sp. is quite common and found on many blooms other than orchids. I had been curious to see if the presence of the polypropylene fabric might deter pollinators but it apparently does not as evidenced by the poor bee. It is an effective blocker to bee passage and therefore a great mechanical aid to my investigations.

Here is a bumblebee pollinator resting near the slit-like opening in the pouch of C. acaule. picture

When a pollinator enters a lady's-slipper pouch, it finds it difficult to exit except by passing either of the two anthers located on either side of the stigma at the back of the flower. Here we see a hoverfly that was able to fit but got stuck to the pollen because its strength was insufficient to pull away from the sticky material adhering to the thorax. picture (I examine every single flower in a population having some 1200 flowers. Occasionally, we find such examples and photograph them for the record. It is not a 'staged' shot.)

If an insect visitor is just the right size and strength, it can exit a flower but while doing so picks up some pollen on its body. If that insect visits another flower, some of the pollen may be scraped onto the stigma as the creature passes through the flower. Looking at the stigma from inside the pouch, we can see the yellow pollen deposited on the stigma. picture

After pollination, fertilization is delayed for about 25 to 35 days. During this time, the ovary is readied. The ovary swells and elongates but if fertilization is unsuccessful, the ovary yellows, withers and dies. The ovary of Cypripedium is unilocular versus being divided into compartments. Here we see developing seeds of C. parviflorum var. pubescens in a capsule cut open in cross section at 60 days after the flower first opened. This is the point at which seeds begin to acquire desiccation tolerance as seen by the darkening seed coats. picture

Seeds of many species take about 70 days to mature but capsule dehiscence may not happen for another month or so. Cypripedium seeds are notorious for being difficult to germinate. Embryo culture has been employed successfully to overcome this hurdle. Seeds are harvested before the seed coat becomes brown. Pictured is a mature seed of the Showy Lady's-slipper, C. reginae. The outer coat (testa) is inflated but there is a very impermeable inner coat (integument) adhering to the embryo and this must be breached if the embryo is to be able to take up water in the germination process. picture

Cypripedium parviflorum has been used as the seed parent in 10 of the 11 registered hybrids using this species. Four of six hybrids registered having C. parviflorum var. pubescens as a parent have variously been made with it as the seed parent. Other horticulturally popular North American species include C. acaule, C. candidum, C. montanum and C. reginae. One beautiful hybrid cultivar is Cyp. Maria 'Glasgow' (parviflorum x macranthos). The name synonym is Cyp. Gisele. picture

Cypripedium arietinum, C. californicum, C. fasciculatum, and C. guttatum present intriguing horticultural possibilities but have not as yet been registered as hybrid parents although most are available as artificially propagated stock. One useful conservation initiative would be to identify and document the variation in fertility and other characteristics of existing populations. Without an understanding of the variation within and between populations, we risk losing a precious resource for future conservation and horticultural initiatives.

I would like to inform you about the International Orchid Conservation Conference planned for Sarasota FL next May. There are sure to be presentations about Cypripediums and other native orchids.

I am now happy to answer any questions you may have concerning the lady's-slippers.

N_Calif_Kathy
I take it that these varieties of Cyps (like parviflorum) have not been separated by DNA yet?
Also that hybridization is in its infancy because these are hard to grow in captivity, even though many of these species are available from legal sources.

MarilyninOttawa
Yes they have Kathy. Martha Case and others have looked at the genetic structure. Some differ by only a very little.

Hybridization got off to a roaring start but with a limited gene pool of seed and pollen parents. It may matter a lot (as in tropical orchids) which individuals are chosen to be seed and pollen parents. These plants are not all identical even though they may superficially look the same.

N_Calif_Kathy
I noticed you made a point of which were seed parents. I thought you may have pointed that out because one species may have made a better pod carrier than another.

MarilyninOttawa
We have looked at individual behaviour in the Large Yellow and found plants with poor pollen and plants which when mated with particular other individuals, produced vigorous offspring. We must start breeding programs with vigor in mind.

That could certainly be the case Kathy or it may have simply been a case of having certain species in stock and seeking pollen from a range of parents to see what worked. As I said, it is unwise to base a breeding program on a narrow range of individuals. It is best to start with a range of say, five individuals of each parent then cross between them to see what happens. It is not any different with Masdevallias or Epidendrums. These plants are individuals. I did not deal with all the various hybrids as I do not have many pictures to show. In general, the yellow color dominates and in fact, is likely a desirable shade. What often happens as with Paphs, is that we get 'toad' colors or muddy rose purple and a mottled effect. Some are good though but a lot need to be grown to find the few winners.

Steve_in_the_Adirondacks
In just the 4 Cyp pictures I showed, some have a nearly round pouch and twisted petals and others have a long pouch and flat petals. They are all from the same location.

MarilyninOttawa
Steve, I have noticed similar variation in our populations. I use variations in staminode markings and pouch shape to differentiate between individuals growing together in a supposed clump. Sometimes a clump is of several plants which grew together.

barbara_in_no._CA
What do you pot these plants in?

MarilyninOttawa
Depending on the type of Cypripedium, they are usually potted in composted bark mix with perlite. Those needing lime have some oyster shell or similar medium added. A lot depends on the need for moisture verus a drier compost and whether or not they prefer acidic or lime conditions.
Seed-raised stock may grow in a wider range of potting media than wild material. The seedlings are more vigorous. The roots should be packed with starch giving the plants a head start when placed in pots. What is most important is the soil temperature. The roots of most North American species should be cool even if the air above is warm. Cyp. formosanum is one of the most easy to grow species. Well worth a try.

N_Calif_Kathy
Some folks have a knack for growing and blooming these. Wilford Neptune does well with them. He's written up his potting recipe on Carson Whitlow's webpage. Of all of us here I think Steve should start his hybridizing program, and soon!

Steve_in_the_Adirondacks
In that case, I had better locate a 2nd species! I bet acaule would be hard to cross with the others. The pouch shape is so different, I wonder what else is different? Chromosome count?

MarilyninOttawa
C. acaule will breed with a range of species although crossing pink with yellow will not always produce the best flower color. Of course, you are also breeding acid-loving species with perhaps a species that prefers buffered soil. The chromosome number is the same as far as I know but what is on the chromosomes is quite another matter. Mismatching can lead to difficulties and loss of vigor.

Removal of wild-collected species for garden purposes is likely a death warrant for the plants. We should only ever buy seed-raised stock which is now available from a range of reputable dealers.

-end

Prechat Handout

Orchids with names beginning with 'C' - Cypripedium

Copyright Marilyn H. S. Light 2003

Cypripediums are mainly temperate terrestrial orchids of Asia, Europe and North America. China is the centre of generic diversity where, according the Cribb (1997) in 'The Genus Cypripedium', two-thirds of the 45 species have been observed. About 25% of the genus is known from North America. Three species are reported from Mexico and eleven other species are found in the continental United States; eight of these also being found in neighbouring Canada. Chen Sing-Chi compared the orchid floras of temperate North America and Eastern Asia in a paper published in the Annals of the Missouri Botanical Garden 70: 713-723, 1983, where it was pointed out that more than two-thirds of the temperate North American genera have a phytogeographic link with eastern Asia orchid genera. Two Cypripedium species pairs are linked. The Ram's Head Lady's-slipper, C. arietinum is found in eastern North America and its Asian counterpart, Cyp. plectrochilum, is found in eastern Asia. The Showy Lady's-slipper. C. reginae, has as an Asian counterpart, C. flavum. Molecular evidence supports the close relationships. What led to this disjunct distribution is not clear but it seems that these pairs and those of other orchid genera share a similar distribution.

Cypripediums are commonly know as 'slipper orchids' because of the characteristic slipper-shaped lip or pouch. There are two anthers located on either side at the foot of the column and a sterile anther (staminode) which faces outwards partly blocking the pouch entrance. The genus Cypripedium is temperate in distribution while its counterpart, Paphiopedilum, is tropical. Members of the genus Paphiopedilum have stiff leaves which are not deciduous whereas members of the genus Cypripedium have soft, plicate leaves. Paphiopedilum flowers separate from developing ovaries or detach from the ovary upon fading. After a Cypripedium flower is pollinated and has faded, it remains attached as a withered remnant to the developing ovary.

Cypripediums are long-lived rhizomatous deciduous perennials. They may exist singly or as clumps of stems connected by a stout rhizome. Roots are often long, hairy and fibrous. Cypripediums may grow in acidic soil as with C. acaule or in calcareous soil as with C. parviflorum. There are species which prefer 'wet feet' including C. reginae. Others such as the European C. calceolus grow in drier conditions. Some like the Stemless Lady's-slipper (C. acaule) and western North American C. fasciculatum have just two leaves nestled close to the ground but most others have three to eight-leaved stems bearing one to several flowers. Cypripedium californicum bears many flowers, one in almost every leaf axil. Many Cypripedium species are spectacular in bloom with flowers lasting up to four weeks.

The most widespread group in North America are the yellow-flowered lady's-slippers, Cypripedium parviflorum and its several varieties. This species is known from northern Ontario in Canada to Texas and from Newfoundland and Labrador in the east to Alaska and British Columbia in the west. With such a wide distribution, geographical separation of members of the yellow-flowered group has given rise to forms that vary in plant characteristics and preferred habitat, and in flower size, colour, shape, scent, and pollinators. Variability in the yellow-flowered Cypripediums can be as great within as between populations. There are natural hybrids between species such as C. candidum and C. parviflorum var. pubescens and some of the these hybrids can be challenging to distinguish from the parental stock.

Cypripediums attract pollinators but seem to offer no reward to flower visitors. Various native bees and bumblebees are frequently cited pollinators but hover flies and even beetles have been known to visit flowers. When a pollinator enters a lady's-slipper pouch, it finds it difficult to exit except by passing either of the two anthers located on either side of the stigma at the back of the flower. If the insect is not too large it can exit but while doing so picks up some pollen on its body. If that insect visits another flower, some of the pollen may be scraped onto the stigma as the creature passes through the flower. After pollination, fertilization is delayed for about 25 to 35 days. During this time, the ovary is readied for the event. The ovary swells and elongates but if fertilization is unsuccessful, the ovary yellows, withers and dies. The ovary of Cypripedium is unilocular versus being divided into compartments. Seeds of many species take about 70 days to mature but capsule dehiscence may not happen for another month or so. Cypripedium seeds are notorious for being difficult to germinate as the seed acquire dessication tolerance during the maturation process. Embryo culture has been employed successfully to overcome this hurdle.

Cypripedium parviflorum has been used as the seed parent in 10 of the 11 registered hybrids using this species. Four of six hybrids registered having C. parviflorum var. pubescens as a parent have variously been made with it as the seed parent. Other horticulturally popular North American species include C. acaule, C. candidum, C. montanum and C. reginae. These four species have been used to create 10 hybrids. Cypripedium arietinum, C. californicum, C. fasciculatum, and C. guttatum present intriguing horticultural possibilities but have not as yet been registered as hybrid parents although most are available as artificially propagated stock. One useful conservation initiative would be to identify and document the variation in fertility and other characteristics of existing populations. Without an understanding of the variation within and between populations, we risk losing a precious resource for future conservation and horticultural initiatives.