Mexipedium xerophyticum
This is one of the most prized orchids in my collection and I treasure it. I purchased it from Russ at Looking Glass Orchids just outside of Asheville NC, and as a side note, I highly recommend checking this place out if you have the chance. His collection is heavily geared towards slipper orchids and his prices are incredible for what you get.
Mexipedium xerophyticum is something of an anomaly within the slipper orchids. This Mexican species from Oaxaca is an evolutionary "missing link" between the South American Phragmipedium orchids and the Pan-Asian Paphiopedilum orchids. The flowers are tiny (size of a US dime coin) and proportionally small even given the small size of the foliage. It's more of a botanical curiosity than a prime-time showy orchid, but what it lacks in size, it more than makes up with rarity and charm.
These were only fairly recently discovered in the past 20 - 30 years. The original colony that was discovered was destroyed in a wild fire, so for quite some time, they were presumed to be extinct in the wild. Fortunately, additional populations have been discovered, but it is still exceedingly rare and quite endangered.
The species name, xerophyticum, reflects the fact that these grow in arid regions, albeit in "oasis" areas that get plenty of water through parts of the year. The foliage is small, but very succulent, and they tolerate periods of drought quite well. I grow this in bright light, but far from full sun. It gets copious watering from spring through fall, and then I cut back significantly during the winter. It never sits in water, which is how I grow some of its close relatives in the genus Phragmipedium. This is grown in a bonsai pot (bulb pot) in small, seedling sized fir bark with medium charcoal and medium perlite. It's susceptible to rot if over watered, particularly if over watered in the winter.
The growths are small, but they produce long rhizomes, so this is a spreading plant. I struggle to keep it in its pot. The new growths develop at the end of lengthy, fragile rhizomes. I'd be embarrassed to admit how many of these new growths I've accidentally broken off in my attempt to keep the plant contained in its pot. This will be repotted after it finishes flowering as it's been in this pot for a few years now. The mix is starting to break down, as evidenced by the minute little brown mushrooms that occasionally pop up.
The flowers are produced sequentially, 1 - 3 at a time on a spike. The spikes are branched similar to the way that Phragmipediums sometimes produce spikes, so that means a spike will often have several flowers open at once. Currently there are 3 spikes on the plant, though I suspect a few more are on the way.
Given the rarity of this plant, they can be on the expensive side to acquire ($100 USD for a multigrowth plant isn't unreasonable). That being said, if you are interested in getting one, I highly recommend spending the extra money on a mature size mulitgrowth plant. They are very slow and difficult to grow when they are seedlings or small divisions. Once they get some size on them, though, they aren't that problematic to grow and bloom reliably so long as you reduce watering in the winter.