Cypripedium flavum, the yellow Cypripedium of western China

In his book Native Orchids of North America, Donovan Correll wrote of an extremely disjunct population of the showy lady slipper (Cypripedium reginae) said to be found in the mountains of western China. That was an eyeful for me at the time (I was 16) – how could that be? China was literally on the other side of the world! Surely, some strange force was at work here. Years later I learned of the yellow counterpart to C. reginae growing in western China’s fabled mountains, the now well known Cypripedium flavum.

These two species are at once highly reminiscent of each other, and yet obviously different, something Correll didn’t notice in the dried herbarium specimens he had examined. Indeed for many years, with the “Bamboo Curtain” fully drawn, many Chinese orchids fell into near mythical status – unknown except by the handful of botanists who roamed those far regions a hundred or more years ago. This is the story of this lovely slipper orchid today.

Cypripedium flavum is a deciduous, herbaceous, perennial, terrestrial orchid found in thin woods of high mountain valleys. It’s fleshy, densely pubescent stem can grow nearly as high as C. reginae, up to 60 cm tall in large specimens, but is usually two thirds that height. Also, like C. reginae, it bears many pubescent, elliptic leaves, as many as 10 in number, in a alternating pattern up the stem. The rhizome is stout, bearing many thick, light brown roots. Plants tend to clump, with 15 or more stems each, but can occur singly.

The flower again is much like in C. reginae, but smaller, having a natural spread of 4-6 cm on average (or as Dr. Phillip Cribb says, “flowers the size of ping-pong balls”). The dorsal sepal and synsepal are very broad to the point of being nearly ovate, the former hanging in a horizontal position like a hood over the lip, the latter, cradling the bottom of it. The petals are more elongate and in most plants tend to recurve backwards. The lip is rather round to somewhat elongate, sometimes having a slight cleft “chin” appearance, and often is laterally compressed.

Flower color is variable, usually being a yellow to cream base throughout. The petals and sepals can be flushed, spotted, and striated with varying amounts of purple-maroon color, or can be completely unmarked. The same goes with the lip – it can be highly spotted, lightly so, or not at all. The staminode tends to be deep maroon, but Cribb cites specimens with “butter-yellow staminodes” from northern Sichuan. Alba-like forms have been found as well in northern Yunnan with nearly pure white flowers – except the staminode which retains some purple pigment. Flowers are borne singly, or very rarely in a pair.

Cypripedium flavum is a plant of high mountain valleys, found only in western China from northern Yunnan, a tiny part of eastern Xizang (Tibet), throughout western Sichuan, southern Gansu, and western Hubei. It probably also occurs in parts of southern Shaanxi, but is not reported from there.

This rare yellow slipper orchid is an endemic species confined to alpine valleys from ~2,300-3,700 meters elevation in the Hengduan Mountains of western China. It seems most at home in areas where limestone is near the surface, sometimes numbering in the thousands of plants, such as northern Sichuan’s Huanglong Valley with its famous travertine limestone formations. It can also be seen on limestone scree slopes, in thin coniferous forests or forest margins, in deciduous woods, and in thickets and scrub. It is often accompanied by other Cypripediums in the wild – typically C. calcicola, C. tibeticum, and C. bardolphianum, and occasionally C. farreri, C. franchetii, C. margaritaceum, C. guttatum, and C. plechtrochilum.

The first images I ever saw of this species on the internet drove my imagination wild, back in the day when dial up was king and jpegs were small and had poor resolution. What I saw were flowers that looked brilliantly yellow and otherwise nearly identical in form with C. reginae. Years later Cribb’s monograph The Genus Cypripedium put things into perspective – this was no brilliant yellow colored version of C. reginae, but rather something quite different.

In June 2013 I was fortunate enough to visit the only place in the world this species is found naturally, the great mountain chain just east of the Tibetan Plateau, the Hengduan Mountains. In the far north of Sichuan Province I finally got to see it face to face, first at Dr. Holger Perner’s nursery at Huanglong, and then again here and there in the nearby wild valleys. What I found was surprising. The flowers and plants were a bit smaller than I had imagined, and the variation of flower color in any given colony was extreme. What follows are the various forms I saw in the wild, a couple nice cultivated plants, plus a “semi-alba” flower native to northern Yunnan.

A fairly typical flower form in northern Sichuan has cream to light yellow flowers with limited maroon spotting on the uppermost lip and on the base of the sepals and petals. These flowers tended to have fairly strongly laterally compressed lips as well. As with most C. flavum flowers the petals often recurved backwards – a feature not desired for horticultural purposes.

A less common form had red-maroon flushing and striping on all the sepals and petals such that the overall impression was they had a solid purple-pink tone. The lip in these forms tended to have similar spotting as the first type.

A even less frequent form was essentially pure yellow throughout – all except the staminode which retained a dark purple-maroon color. I can remember seeing only a few plants with this coloration and we saw many hundreds of flowers.

An near alba flowered form is found in northern Yunnan province. These tend to be smaller plants in stature than the other types. The lip, sepals, and petals are all a clear creamy ivory color except the staminode which retains some purple pigment. This is a very choice plant for gardeners and often sold under the name “semi-alba”.

In addition to the above forms seen in the wild, we also saw two heavily purple colored forms at Dr. Perner’s nursery in Huanglong. The first form had intense maroon spotting on the ventral sides of the sepals and petals, as well as around the lip orifice. The other one had a lemon yellow lip with many small maroon spots throughout it, and clear yellow-lime sepals and petals. Both were striking flowers and are part of his breeding stock, so if you buy plants from him they are likely to be very attractive forms!

As with many Cyps in western China, this species loves to grow in limestone areas, particularly on travertine – a type of limestone that is formed from the precipitation of calcium carbonate out of mineral water springs (for more see the C. tibeticum article, paragraph 6). Having said that, this plant seems to actually thrive on limestone, preferring substrates with a pH above 7.0. In such areas this species grows in great luxuriant patches, what the botanist Farrer called, “sudden outbursts”, and indeed that is the impression they give – great drifts of flowers exploding out of the surrounding woods. It is a remarkable thing to see mossy islands of scant shrubs and dwarfed conifers brimming with these flowers, growing literally in the midst of travertine streams just centimeters away.

Huanglong Valley is part of the far larger Huanglong National Park, a World Heritage Site, and home to many endangered animals and plants, notably giant pandas and the golden snub-nosed monkey. In our visit there we witnessed thousands of orchids in full flower surrounded by the other worldly beauty of its 3.5 kilometer long travertine formation, complete with waterfalls, steams, and its many aquamarine terraced pools. This amazing experience was marred only by one thing – hundreds of Cypripedium plants had been killed by late season frosts, in particular C. flavum. We saw patch after patch of red-brown scorched clumps instead of flowers. Nevertheless, the display was phenomenal, the plants will recover in coming years, and yet, it spoke to a deeper, perhaps more ominous problem – climate change.

Dr. Perner has witnessed Huanglong’s orchid display for the past 15 years and he has never seen such an event in all that time. Due to peculiarities in weather having to do in part with such high elevations in what is essentially a subtropical area, the climate here is very stable with few perturbations from year to year. And yet over the past decade that stability has been challenged. A late season frost while many plants were in bud is just one symptom of larger changes. Yunnan, just to the south, has been in severe drought for five years now. Many plants are dying or are reproductively at risk due to summer monsoon rains coming too late in the season.

The Tibetan Plateau, just to the east, is a vast icebox of permafrost at a very low latitude, and exerts an enormous effect on much of south-central Asia. From it flow some of the most important river systems including the Yangtze, Mekong, and Brahmaputra, to name just a few. All of these depend on Tibet’s vast land-based ice deposits, which are the third largest in the world after Antarctica and Greenland. And yet we now know that Tibet is rapidly losing its permafrost and all that ice is therefore in danger, along with the rivers and climate of much of south Asia. How this will impact the entire region’s ecosystems and dependent human populations leaves a large question mark on the future. Perhaps one freak spring frost is just happenstance, then again it may be just a taste of things to come.

This plant was first collected in western Sichuan by a French missionary in 1869 and was finally described by Franchet 18 years later as Cypripedium luteum – a name that as fate would have it had already been used by Rafinesque in 1828 to describe a form of C. parviflorum. Though this name was later found to be invalid, the reuse of the epithet luteum was unacceptable. Many years later Hunt and Summerhayes (1966) renamed it C. flavum. Luckily both names mean essentially the same thing – yellow flowered.

Cypripedium flavum is a member of section Obtusipetala, a group only shared by two other species, the aforementioned C. reginae and the truly boreal North American species, C. passerinum. To date no known naturally occurring hybrids have been found, something that is not totally unexpected. A number of artificial hybrids have been made, with C. Ulla Silkens being one of the oldest and most recognized. Being a product of the cross with C. reginae, the plant and flowers are somewhere in-between the two species, and yet highly variable in color – some are nearly pure white, some heavily spotted, and a few that are near dead ringers for C. reginae. The oddest hybrid I’ve heard of is C. Ilse, with the other parent being C. californicum!

In the horticultural trade there have been quite a few varieties designated, mostly due to flower color. It would be interesting to see if such forms breed true, but based on what I saw in the wild many of these live side by side, hence they probably are not genetically pure. The near white flowered form of Yunnan seems to be a more distinct entity, but I imagine that the spotted flowers, “red petaled forms”, and pure yellows are a real grab-bag.

With the opening of China’s borders in the early ’90s, collected plants of this species began to show up on the world market – principally in Japan, Europe, and North America. Instead of being a relatively easy plant to grow like its near cousin, C. reginae, many found it to be rather finicky, dying out within a few seasons.

Exactly what the problem was remained uncertain, but over time specific requirements this species demands for good health have become more apparent. The following are guidelines for growing this species successfully.

First and foremost, this plant requires cool to cold growing conditions to thrive. Research by Chinese scientists has shown that photosynthesis for this species is optimal around 18-20 C, and rapidly diminishes with each degree higher. Plants subjected to over 25 C literally “shut down”, starving to death, so to speak. This need for cool growing conditions (similar to C. guttatum and C. passerinum) puts a serious limitation on where this plant can be grown successfully. Check out this pdf of their research to see the findings.

Many areas in eastern North America are not suitable for cultivating this plant since heat waves in summer will effectively finish them off in a few years. Ron Burch has reported success in his zone 5 garden in northern Connecticut, however to keep them going he has to grow them in what he calls “deep shade” – not an optimal situation for this plant. On the other hand, Darcy Gunnlaugson has grown them in Victoria, B.C. in zone 8. The difference is that summer temperatures there are quite cool, in fact nearly identical to those of the mountains of western China.

Another issue is soil pH. The more I hear about this species, the more I would label it a “calciphile” – a lime lover. In this group I would include C. candidum, C. farreri, European forms of C. calceolus, and probably C. wardii. To wit, yes, they all can be grown in neutral to even slightly acid conditions, but none prefer this. So why stress a plant that is already a challenge to grow with too acidic composts? So what pH is best? You’ll have to experiment with your local conditions, but I’d recommend keeping the pH between 7.0 and 7.5. No doubt they can take even higher. Definitely avoid anything below 6.5.

Third, this plant likes light, not shade. It can be grown and even flowered in moderate shade, but clearly prefers either very high shade (as in a high, thin canopy or north facing wall) or at least a few hours of sun. I saw no plants in what I’d call deep shade in the wild, but plants in moderate shade still seemed happy enough to flower. I say this with one caveat, though taller in stature, they tended to have a single growth as compared to plants in more open areas that grew in large clumps and clearly were more vigorous.

To see live video of this species in the wilds of Sichuan, check out this video:

Like all western Chinese Cyps they require drier conditions in winter as compared to Cyps from other regions of the world. The best way to achieve this is to cover their beds with protective covering of some sort in winter. Another way to combat winter wetness is to make sure their beds are well drained. Darcy Gunnlaugson has managed to keep most of his plants happy without winter cover despite his region having a winter “monsoon season”. His trick is perfect drainage in his Cyp beds.

The growing medium should probably be mostly inert ingredients such as pumice, non-acidic sand, perlite, baked clay, and the like. I would grow it in a similar substrate as C. tibeticum since they live side by side in nature – say one part perlite (or pumice), one part sand, and a generous overburden of conifer needles worked into the top layers of the compost. For this species I’d ensure sweet conditions by adding lime on a regular basis.

During growth give them plenty of water and fertilize regularly. Lower concentrations of fertilizer, applied frequently with generous flushing of beds and pots with pure water between applications, is recommended. If happy this species is fast growing and will benefit from regular feeding.

This plant is optimally grown in cool summer areas with long, unbroken winters. In the eastern US that would include only the northern tier states and adjacent areas of Canada. In the west it may be grown perhaps even down into coastal Oregon. It is difficult to talk about USDA cold hardiness zones for this plant. In cool summer areas it can be grown even to zone 8, in regions that experience hotter summers, zone 5b and lower seems appropriate. If you experience hot summers, even for a relatively short period, I would not recommend trying to grow it.

Fortunately, this species has been grown from seed with great success. At the present time, Europe has the best sources, though Ron Burch has offered it though his nursery, The Gardens at Post Hill. Dr. Holger Perner also has many in production in China. See Hengduan Mountain Technology’s website for more about importing plants from him.

If you have cool summer conditions this may be a plant for your garden. I can only look on with envy since the baking summer heat of southern Japan (my home) would be the death of it quick! At least I have my memories of this wonderful slipper orchid in its wild home to savor.