Mexipedium xerophyticum, note the small size (in a 2.5" pot).
An excellent review of the discovery and habitat of this plant is presented by Marilyn LeDoux (1996). The plant was first collected and presented as a pressed herbarium specimen in 1985. The site was revisited in 1988 and live material was collected. The plant was described by Soto et al in 1990, and transferred to it's own genus by Albert and Chase in 1992, based at least in part on it's unilocular ovary more reminiscent of Paphiopedilum and Cypripedium than Phragmipedium's trilocular ovaries. This transfer is not universally accepted (see Koopowitz (1995)).
The habitat is said to be restricted to one isolated locale in Oaxaca, Mexico, where it grows on exposed steep cliffs with a north and east exposure, shielding it from full mid day sun. It is also said to grow both directly on the rock and in accumulated detritus in crevasses in the rock, with the latter being the habitat the plant is more vigorous in.
Average Monthly Rainfall
The plants grow at an elevation of 1,050 feet (320 m) and receive an annual rainfall of about 98 inches (250 cm), but as you can see from the accompanying chart derived from data published by the Bakers (1991) the rainfall is far heavier from June through November, and very much reduced from December to May. They also grow in very warm conditions year round, with approximately an average 10F diurnal variation (chart again reproduced from data published by Baker and Baker (1991)). The small, stiff and semi erect thick leaves indicate that this is a plant capable of withstanding some very harsh conditions.
Average Monthly High and Low Temperatures
We grow this plant best in a mix containing approximately 40% #3 charcoal, 50% fine fir bark and 10% perlite. This makes for a dense but quick draining and drying mix. Because the plants are in a less moisture retentive mix they do dry out somewhat in between waterings. We fertilize virtually every watering at the same rate we use for our Paphs. Our irrigation water is RO, and the water/fertilizer pH is adjusted to approximately 6.5 This is the only "Phragmipedium" to grow in association with limestone, and we do grow it with a top dressing of crushed oyster shell similar to how we grow calcicolous Paphs.
Closeup of Mexipedium xerophyticum Flower.
We grow it with the strap leaf Paphs, but it would probably do well also with Phrag caudatum as long as the mix is kept a little less moisture retentive. The plants receive about 2200 to 2500 footcandles of light at the maximum, probably much less than they receive in the wild. Some growers report good successes with these plants at much higher light levels, but compromises have to be made in the mixed collection.
The plants can roam quite a bit by putting out quite long rhizomes, when this occurs it is best to place another pot under the errant growth, and gently anchor the base onto the pot with a piece of wire until it is fully rooted. Then you can severe the rhizome if you wish. We have tried to select plants with a shorter rhizome for reproduction, but only time will tell if we've been successful.
The plants flower for us in the spring.
Rhizome Heading Out of the Pot.
Mexipedium xerophyticum has proven quite easy to germinate in the laboratory, but a bit more difficult to grow up in flask and compot. However, it is becoming somewhat more available with time as progress is made in learning to overcome these obstacles. Hybrids have also been generated with Phragmipediums, however to the best of my knowledge none have yet bloomed.
References:
Albert, V. A. and M. W. Chase. 1992. Mexipedium: A New Genus of Slipper Orchid (Cypripedioideae: Orchidaceae). Lindleyana 7 (3): 172-176.
Baker, M. L. and C. O. 1991. Orchid Species Culture: Pescatoria, Phaius, Phalaenopsis, Pholidota, Phragmipedium, Pleione. Timber Press, Portland, Oregon.
Koopowitz, H. 1995 The Diminutive Phragmipedium xerophyticum. Orchid Digest 60 (3): 123-128.
LeDoux, M. 1996 Phragmipedium xerophyticum and its Culture. Orchid Digest 59 (3): 108-110.
Soto, M. A., G. A. Salazar and E. Hagsater. 1990. Phragmipedium xerophyticum, una nueva especie del sureste de Mexico. Orquidea, 12: 1-10.
