1996 - Cultivation & Propagation
THE DIMINUTIVE PHRAGMIPEDIUM XEROPHYTICUM
Marilyn LeDoux
Orchid Digest 60(3): 122-128. 1996
Marilyn M. LeDoux is a probationary American Orchid Society judge in the Mid-America Region.
Phragmipedium xerophyticum (Soto, Salazar & Hagsater, 1990) is a unique new species from southeastern Mexico. The specific epithet, xerophyticum, refers to its relatively dry habitat and to its vegetative characteristics, namely thick, succulent leaves which are very different from all other phragmipediums. The plant itself is quite small and has diminutive white flowers with a pink tinge.
Discovery and Habitat
A very peculiar pressed-plant specimen collected in September 1985 by Heriberto Hernández in Oaxaca, Mexico was sent to the herbarium of the Mexican Association of Orchidology (AMO) for identification. It was among material collected by a group of collaborators of Dr. Thomas Wendt of the College of Graduate Studies of Chapingo. The plant had fan-like leaves joined by very long rhizomes and a developing pubescent apical inflorescence. A second specimen of the same collection had just one flower, enough to confirm suspicions that it was a member of the Cypripedioideae subfamily, and probably of the genus Phragmipedium. An excited Eric Hagsater, Gerardo Salazar, and Miguel Soto of AMO organized a collection trip as soon as possible to the locality to obtain live material.
In September 1988, Mr. Hernández took them to the site of his original collection in the warm and humid region of Oaxaca, an area of very rich and diverse flora . Here the jungle consists of an impressive and extensive evergreen tropical rain forest with patches of oak, pine, and sweetgum forest. Near a river there is a group of north-south oriented hills that end abruptly to the north in karst (limestone) outcrops, with a xeric plant community dominated by Beaucarnea, Agave, low trees of Plumeria and Pseudobombax, and an orchid (Cyrtopodium paniculatum).
This very interesting vegetational "island" is found within the realm of the rain forest and is the only known locality of Phragmipedium xerophyticum. The plants are not abundant and it took the collectors quite a while to find the specimens they were seeking. The plants grow on vertical cliffs without trees, in small cracks with humus or on the exposed rock. The cliffs face north and east so the plants are not totally exposed to the full intensity of the midday sun. The strongest plants are growing in humus and not on naked rock. The elevation is 320 meters (1,050 feet) above sea level. The area receives about 250 centimeters (98 inches) of precipitation annually with a definite dry season during the spring. The average annual temperature is about 25°C (77°F). On this 1988 expedition the type specimen was collected and in 1990 Soto, Salazar, and Hagsater published their official description of the plant in the Mexican publication Orquídea.
Plant and Flower Characteristics
Having successfully grown two different cultivars of this species since 1990, most of the plant and flower observations to follow, especially numerical ones, are based upon my experiences. Some comparisons will also be made to the actual plant description published in Orquídea.
Plant
This sympodial species has relatively short, rigid, fleshy light green leaves that are distichous and arranged in a fan shape. My fully mature plants have five to eight leaves and are up to 22 cm in natural spread, although 12 to 18 cm is more common. The basal leaves are very small and the superior leaves are larger. My largest leaves are up to 14 cm in length and 2.5 cm wide, although another grower I've shared observations with reports a leaf over 22 cm long on a plant with a natural spread of over 25 cm (Phragmipedium xerophyticum 'Oaxaca', CBR/ AOS). When the cultivar 'Oaxaca' received a CBR/ AOS award in June 1992 the largest leaf was 8.3 cm long by 1.3 cm wide, so a blooming plant can be considerably smaller than the maximum sizes observed since then. New growths develop from brittle, elongated, above-ground rhizomes which in cultivation are 1.5 to 18 cm long. In its natural habitat described in Orquídea, one cultivar of this species with all its rhizomes and growths covered an area of about one square meter. Roots do not form from the rhizome itself, but only develop when the rhizome begins to flatten out and expand at the tip, forming a new plant.
Inflorescence
The sturdy, pubescent inflorescence is apical, arising from the center of the leaf fan. Under my cultural conditions, both in a greenhouse and under lights, it becomes visibly noticeable between March and June. According to the original description, its total length is 6.5 to 13 cm. In cultivation my inflorescences have been 11.5 to 24 cm long with the aforementioned grower reporting a nearly 32 cm inflorescence. The type of inflorescence is a panicle with one to four branches, though most generally two. Normally the branches bearing the flowers are very short, so that the flowers almost appear to come directly off the main stem of the inflorescence. I have had two inflorescences with three to four branches in which the lowest branch on each was 5.5 to 6.0 cm long, therefore holding those flowers up and away from the main peduncle. When the panicle does have two to four branches, the apical branch normally develops and begins to bloom first. The original describers felt that the lower branch would probably only develop when the apical one was not going to form more flowers; however, this is not my experience with plants in cultivation. Generally, one to three flowers will bloom on the apical branch, before lower branches begin to bloom. However, on a plant with three branches both the apical and middle branch opened their first flowers on the same day. The flowers on each branch are normally successive with one flower open at a time, but two to four branches can certainly be blooming simultaneously. The original description noted three to seven successive flowers per branch, but in cultivation I have observed up to ten flowers per branch. The cultivar 'Oaxaca' recently had eighteen flowers, ten on the apical branch and eight on one lower branch. The inflorescence bloomed over a six-month period, from the end of April to the end of October. There can be anywhere from ten to thirty-two days between successive flower openings, with the first flowers to bloom usually having the least number of days between them and the last flowers to bloom often having the most.
Flowering
In keeping with small plant proportions, the scentless flowers are also small but showy. The natural flower spread for the cultivar 'Oaxaca' CBR/ AOS is 2.2 cm horizontally and 2.3 cm vertically, or about seven-eighths of an inch. Flower measurements to follow are also from this cultivar. The species has a white flower flushed with pink, especially on the outer surface of the dorsal sepal and on the staminode. The dorsal sepal is 0.7 cm wide and 1.6 cm long. The pointed petals are long, narrow, and arch inward, sometimes with a slight twist. They are 0.3 cm wide and 1.4 cm long. The delicate rounded pouch has incurved margins and an inflated appearance. It is 0.8 cm wide and 1.3 cm in length. The synsepal is 0.7cm wide and 0.8cm long. Individual flowers remain fresh-looking for as long as fourteen days. As the flower starts to fade it wrinkles and turns slightly brown before falling off in a day or so, leaving the ovary to shrivel on the plant and fall off about a week later (if not pollinated).
Classification
The flowers of P. xerophyticum most closely resemble the two species of Phragmipedium in the section Micropetalum, P. besseae and especially P. schlimii, due to their small size and pink flushing. However, both P. schlimii and P. besseae have much wider, more rounded petals. Phragmipedium xerophyticum also lacks the transparent windows at the sides and back of the pouch, though all three species share the trait of inrolled pouch margins which create an inflated appearance. Though the flowers of P. xerophyticum differ somewhat from other phragmipediums, it is the xeromorphic plant habit that very visibly sets this species apart.
In 1992 scientists Victor A. Albert and Mark W. Chase placed P xerophyticum into a genus of its own, Mexipedium, so named because of its country of origin. Their reasoning is as follows, though many others do not agree with this move. Phragmipedium xerophyticum has floral characteristics of both Phragmipedium and Paphiopedilum and therefore does not belong in either genus. Paphiopedilum and Phragmipedium xerophyticum have unilocular (one cavity) ovaries, while all other Phragmipedium species have trilocular (three cavity) ovaries. Some Phragmipedium species, including P. xerophyticum, have branched inflorescences, while Paphiopedilum species have unbranched ones. Finally, all Paphiopedilum species have sepals which overlap in the bud stage (imbricate sepal aestivation); all Phragmipedium, including P. xerophyticum, have sepals which do not overlap but join at the edges (valvate sepal aestivation). Albert and Chase felt it was important not to confuse the taxonomic distinctions between Paphiopedilum and Phragmipedium by including the new species in Phragmipedium. Other scientists disagree, however, including Eric Christenson and Harold Koopowitz. Dr. Koopowitz's arguments against creating the genus Mexipedium are in the July-Aug.-Sept., 1995 issue of the Orchid Digest. Dr. Koopowitz feels that the unilocular ovary in P. xerophyticum is just an adaptation brought about by the small size of the flower and is certainly not enough reason to create a new genus when the species is so closely allied to Phragmipedium in its other characteristics. Dr. Koopowitz also feels that the plant's breeding behavior will shed further light on the plant's relationships. Hopefully, the correct classification of this species will be resolved over time.
Conservation
This species is a very rare plant in danger of extinction in the wild. It is known from only one locality with a very specific habitat, rocky karst areas. The exact locality in Mexico has not been disclosed to protect the seven individual plants that were found. Thankfully, the location is remote and is not accessible at all by vehicle during the rainy season, due to river levels.
Small divisions of the plant were removed by the group from the Mexican Association of Orchidology in 1988 and exported to Phragmipedium experts in the hopes of blooming and propagating the plants by seed with the goal of avoiding plant removal from the natural habitat by illegal collectors. Lucile McCook, who was doing her dissertation on the genus at Cornell University, received two of the cultivars in 1988 which were later named 'Oaxaca' and 'Windy Hill'. The plants were sent under the provisions of CITES for the exchange of scientific material between recognized institutions. In view of this, approval was recently gained from the U.S. Fish and Wildlife Service for the export of artificially propagated progeny from these two cultivars, and growers (exporters) can have them added to their appropriate CITES permits. Seedlings are now available from several commercial orchid establishments. The objective of the original collectors from AMO is being realized and the future existence of the species seems assured, at least in cultivation.
- Phragmipedium xerophyticum ‚Oaxaca‘ CBR/ AOS.
- Phragmipedium xerophyticum ‚Windy Hill‘. This is the type specimen clone.
- Phragmipedium xerophyticum ‚Windy Hill‘. The panicle has three branches. The Iowest one being unusually long and the two upper ones very short as they normally are. Note the plant and rhizome habit below.
- Phragmipedium xerophyticum ‚Oaxaca‘ CBR/ AOS.
- Looking down on the plant.*
- Looking down on the plant (with a ruler for scale).*
- Close-up of plant growth habit.*
- This panicle has four branches although one has aborted and will not produce flowers. The lowest branch is unusually Iong and the upper ones are very short as they more commonly are.
- Front view of the flowers shown in the previous photograph.
* Notice individual pots taped together and new plantlets just beginning to form on pots with fresh New Zealand sphagnum moss.
Culture
Having grown this species over five years both in a greenhouse and under lights and bloomed it for the past four, I feel confident in sharing the cultural techniques that have been successful for me.
First, it is important to consider the natural habitat of the plant: warm, humid, growing on karst rocks or in humus in the cracks of the rocks, on east- or north facing cliffs.
Light
I grow P. xerophyticum with all my other phragmipediums, and light conditions are essentially the same for all. Under artificial lights I use a "Suncircle" for revolving light with one 1,000-watt metal halide bulb and one 1,000-watt high-pressure sodium bulb. Day length is increased in summer and decreased in winter to approximate natural conditions; however, the plant's blooming period can probably be changed by adjusting this factor.
Phragmipedium xerophyticum receives 2,000 to 4,000 footcandles of light depending upon bulb locations when the readings are taken. The grower I mentioned earlier for growing very large plants, reports giving his plants 5,000 to 7,000 fc. He attributes his larger plants to the very high light and giving weak fertilizer applications with almost every watering. He believes that this much intense light is probably excessive because his flowers did not have their normal pink flushing and the petals were irregularly twisted. The inherent heat accompanying these light levels, even with fans for rapid dissipation, also probably contributes to these abnormalities in the flowers. A recent inflorescence on his cultivar 'Oaxaca' did, however, reach 32 cm with three flowers open simultaneously and five visible buds present.
Temperature
Under lights, my summer temperatures run approximately 68° to 70°F (20° to 21 °C) at night and 82° to 85°F (28° to 29°C) during the day. Winter temperatures are 60° to 65 °F (16° to 18°C) at night and 75° to 80°F (24° to 27°C) during the day. In the greenhouse the extremes are greater, with 55° to 58°F (13° to 14°C) on winter nights and at least 90°F (32°C) on hot summer days. The plants under artificial lights have done better, perhaps due to temperatures more to their liking. Climatic data from a site in Mexico similar to the species locale indicates that summer nights average about 70°F (21°C) and days average 83° to 84'F (28° to 29°C). Winter temperatures there run 63° to 64°F (17° to 18°C) at night and 73° to 74°F (23°C) during the day. These temperatures correspond quite closely to my temperatures under lights.
Humidity and Air Circulation
The humidity of the region from which the species originates is very high year around, 80 to 90 percent, even during the dry season. This is difficult to duplicate under lights, but I do try to maintain at least 50 percent humidity, with it rising to at least 80 percent after watering. In situ the plants experience heavy dew deposits daily; under lights I simulate this by daily early morning misting. Plants growing on exposed cliff faces will naturally be exposed to excellent air movement, which I provide with wall-mounted fans.
Watering and Fertilization
As the former grower of at least 10,000 orchid plants at the Missouri Botanical Garden, I learned that the best way for me to deal with the different water needs of so many kinds of orchids and get my watering chores done efficiently was to adjust the potting mixes to hold more or less moisture, and then water nearly everything in pots at the same time, unless plants needed a dry or nearly dry rest period. l treat P. xerophyticum in this fashion and put it in a slightly coarser mix than my other phragmipediums but water it at the same time, every two to four days depending upon how fast all my plants are drying out. ln nature, the plant experiences a definite dry season during the spring. In cultivation, l have kept the plant somewhat drier for a month or two during March and April while still misting it daily, and have also just ignored its dry season with equal results. I water with a weak fertilizer solution, about one-quarter strength, at least every two weeks.
Potting Medium and Special Techniques
My normal Phragmipedium mix is the following: nine quarts fine bark, three quarts extra-fine charcoal (1/8" to 1/4"), three quarts loosened Canadian peat, three quarts perlite, one-half cup bone meal and one-quarter cup dolomite lime. To any portion of this mix separated out to use for P. xerophyticum I add one-quarter more charcoal for drainage. For example, for two cups of the above mix, I add an extra one-half cup of extra fine charcoal. Probably most well-drained mixes will work for this species as long as dolomite lime is in the mix. I think it is important because the karst area from which the plant originates is composed of relatively soluble limestone rock.
I use a special technique that I feel contributes to my success in growing and blooming the species. The rhizomes sent out by the mother plant are usually too long to be contained in the pot without putting the plant into a larger pot. I recommend strongly against this practice since the plant will likely languish and not grow vigorously. As the rhizomes grow over the edge of the pot, I mist them daily. When they begin to flare at the end to begin plantlet formation, I put a 2.25-inch plastic pot filled with medium and topped with a thin layer of New Zealand sphagnum moss under the new growth and tightly tape this pot to the mother pot for stability. If the stolon is too long to do this, another pot can be taped upside down in between the plantlet's pot and the mother pot as a spacer. Be careful in working with the plants because rhizomes are quite brittle and easily broken. Once the newly forming plantlet has a pot and medium under it, I use a thin strip of waterproof tape over the top of the rhizome behind the new growth and attach it to the sides of the pot to hold the rhizome firmly down to the sphagnum moss until it is securely rooted. I mist the sphagnum moss daily to keep it moist without keeping the medium soggy underneath to encourage rooting. With other environmental factors being favorable, the plants will flourish using this technique, and new rhizomes will be continuously produced.
My experience is that a rhizome cannot necessarily be kept shorter by putting a favorable rooting medium under it when it is short. It will often still grow over the edge of a new pot of medium and into mid-air before it begins to flare out for plantlet formation. However, very often when it hits an obstruction, such as a pot edge, it will stop growing and produce a plantlet. By planting the mother plant deeper in the pot more plantlets should root within the original pot to achieve a fuller look. If the developing plantlet finds no medium to root into, it and the entire rhizome will eventually die.
I grow P. xerophyticum in plastic pots because I am always taping the pots together and taping new rhizomes down to the pots. Small pot size is important because it simulates the small crevices in the rocks where the plants grow naturally. I grow single growths in 2.25-inch to 2.5-inch pots. With two growths close together I use a 3-inch pot, and with three close growths I use a 3.5-inch pot.
Propagation
Division: As soon as the new plantlet is well rooted and about half grown it may begin producing its own rhizomes and can be removed from the mother, if desired, by severing the connecting rhizome. However, I have observed that the new plantlet will grow faster if left attached to the mother plant a little longer, at least until its own first rhizome begins to flare out and begin plantlet formation. It has been my experience that the mother plant must have plantlets to initiate the inflorescence. My friend found, to his dismay, that taking all of the plants from the mother cost him an inflorescence. After new stolons were anchored and began plantlet development, the mother plant developed an inflorescence.
Seed: Pollination has been most successful when done three to four days after the flower is fully open. Due to the flower' s small size and delicate texture it is very difficult to do without damaging it, especially the pouch. However, pollination has been successful for me even with the pouch torn off as long as the stigma is not damaged.
Seed-capsule maturation times (dry pod) for species seedling production have been extremely variable, from 114 days for a selfing of the cultivar 'Windy Hill' to 276 days for a selfing of the 'Oaxaca' cultivar. This seems to be dependent upon environmental conditions, especially temperature, with the 276-day capsule being subject to 55° to 58°F winter night temperatures in a greenhouse. Average capsule maturation times under warmer, more stable light room conditions have been 155 days for 'Windy Hill' capsules and 160 days for 'Oaxaca' capsules. All conditions being equal, the 'Windy Hill' cultivar always matures its pods before the 'Oaxaca' cultivar. When the capsule is mature it is about 3.5 cm to 4.5 cm in length by 3.0 mm in width. Since the capsule is relatively small, seed quantity is also reduced compared to Phragmipedium species with large capsules.
I have sent seed capsules to several labs which guard their processes and formulas carefully; however, I do know that a relatively mild flask medium should be used. It is very easy to burn the protocorms and seedlings.
Hybridization
Phragmipedium xerophyticum does appear to hybridize readily with other phragmipediums. The results are yet to be seen, as the seedlings are still in the lab. Capsule maturation times for hybrids have averaged 150 days with P. xerophyticum as the pod parent, but like the species itself, this is very dependent upon environmental conditions and the cultivar used . Capsule maturation times using the other species as the pod parent will correspond to the natural maturation time for the particular species used.
One obvious goal of breeding with this species is plant size reduction. Picture large Phragmipedium plants with very long petals such as P. wallisii, P. caudatum, or P. Grande "miniaturized" by crossing them with P. xerophyticum. Although we don't know which traits will be dominant and which ones recessive in breeding with this new and very different species, the results will be exciting to see.
Breeding with P. schlimii has been somewhat of a plant size reducer in the past but pink is nearly always the dominant color in the progeny. By breeding with P. xerophyticum instead with its near-white flowers, perhaps the colors of the other parents will be exhibited. Also, by breeding P. xerophyticum with other very pale parents, perhaps near-whites can be produced in hybrids.
The narrow, incurved petals which contribute to the dainty look of P. xerophyticum are perhaps its poorest feature to pass along to its progeny when judging standards are considered. Its long space between growths is also an obvious disadvantage in breeding, as a neat tidy plant may be hard to produce.
Another desirable possibility in breeding with this species is Phragmipedium-Paphiopedilum hybrids. Seedlings are germinating between Phragmipedium xerophyticum and several Paphiopedilum species in the Brachypetalum and Parvisepalum sections, such as Paphiopedilum niveum and P. delenatii. The species may yet prove to be a link between phragmipediums and paphiopedilums in its breeding characteristics.
AOS Awards and Judging
A Certificate of Botanical Recognition from the American Orchid Society is the only award granted to this species to date. It was awarded on June 27, 1992 in Glencoe, Illinois and was the first known blooming of the species in cultivation. This plant was named ‘Oaxaca’ in honor of the Mexican state in which it was discovered and was exhibited by Dr. Lucile M. McCook and myself. Dr. McCook was one of the original recipients of the species distributed by Eric Hagaster, Gerardo Salazar, and Miguel Soto of Mexico.
A Certificate of Horticultural Merit is a future award possibility for this species. According to the American Orchid Society's Handbook on Judging and Exhibition, a CHM is "awarded to a cultivar of a well-grown and well-flowered species or natural hybrid with outstanding aesthetic appeal that contributes to the horticultural aspects of orchidology." The species is definitely appealing to many orchid growers and its horticultural as well as scientific contributions to orchidology are beginning to surface. A future quality award is also possible if one of the seven cultivars in cultivation or their progeny prove to have superior flowers, or after sufficient blooming demonstrate that the 'Oaxaca' and/ or 'Windy Hill' cultivars are in fact of a superior nature.
Since very few AOS judges have actually seen this species in bloom, when plants are to be judged comparisons should be made to the original description in Orquídea, the CBR award description, and my observations in this article. Unfortunately, Orquídea, is not readily available in judging centers and is written only in Spanish as well. Judges should especially keep the following in mind: when it was awarded a CBR, the cultivar 'Oaxaca' had one flower and two visible buds, with another bud later appearing and blooming. Therefore, not all buds are yet visible when the first flower or flowers are blooming. As I previously mentioned, I have seen eighteen flowers open over a six-month period on one inflorescence. Normally, each branch on the panicle will only have one flower open at a time and two branches per panicle is the norm, while three [four] branches is the most I have observed on one inflorescence in my four years of blooming this plant. To have three flowers open on one inflorescence at the same time (as was recently demonstrated by another grower of the 'Oaxaca' cultivar) is exceptional. The wiry inflorescence is sturdy and should be selfsupporting. Although the petals sometimes have a slight twist, this is undesirable, and ideally both petals will be uniformly arched without twisting. The plant has not been particularly easy to bloom, and a plant with multiple mature blooming growths does not necessarily have uniformly developed inflorescences, a point to consider especially if a Certificate of Cultural Merit award is being discussed by the judges.
I hope this article has been helpful to those orchidists desiring to know as much as possible about this extraordinary and unique little species of Phragmipedium from Mexico. By propagating and growing it successfully, we can assure its protection from extinction.
Acknowledgments
Special thanks go to Salvador Vitanza and Doug LeDoux for translating the original plant description from Spanish, to Tom and Barbara Larkin for their helpful observations and suggestions, to Lucile McCook for sharing divisions of her plants and other information with me, and to Eric Hagsater, Gerardo Salazar, and Miguel Angel Soto for reviewing my manuscript for accuracy, and for additional information provided by Gerardo Salazar.