Pseudolithos migiurtinus - Cactus Club

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Pseudolithos migiurtinus

Plant of the Month > Species O to P

by Bruce Brethauer

Pseudolithos migiurtinus is a rare endemic from dry regions of eastern Somalia. This is one of the most unusual members of the Asclepiadaceae or milkweed family, with highly succulent stems patterned with irregular, rather warty looking, hexagonal tubercles -(podaria) giving this plant the appearance of a curious, rough stone - which is reflected in its generic name, which translates "false rock". In my own minds-eye, the stems of this plant are more reminiscent of the fruits of the Osage Orange tree, a tree which was once widely planted throughout the Midwest and other states to mark property lines and fence rows.

   The stems of P. migiurtinus are initially spherical - but eventually become more egg-shaped  or even columnar as the plant ages. The stems bear 4 rows of small, truncated stems, from which the flower buds emerge. These side stems lengthen very slowly as the plant matures, producing additional flower buds at their apex when conditions are favorable. Plants typically remain solitary throughout their lives, but in photographs of some venerable old plants which I have seen, it appears that this species may eventually produce an offset or two, and the curious peduncles from which the flowers emerge may take on a rather branch-like appearance on very old specimens. The plants are remarkably similar in appearance to some species of Larryleachia, but on the basis of significant differences in their flowers, they are not considered to be very closely related, and that their remarkably similar appearances are probably due to convergent evolution in which two different species have acquired very similar traits as they adapted to very similar environments.

   Curious small starfish-shaped flowers are produced in clusters from the short side shoots of these plants; individual blooms are barely about 1/4 of an inch across. The flowers are of such a deep maroon coloration, that they oftentimes appear to be practically black. The petal tips bear small tufts of hair-like fibers which flutter at the slightest breeze. The greater portion of the petal surface bear minute (practically microscopic), club-like hairs which probably assists the dispersal of the foul aroma of these flowers. Most authorities report that the flowers of this plant produce a carrion-like aroma, but in photographing the flowers of my plant, I detected a scent more reminiscent of cat dung. Either way, the local flies are are drawn to the flowers of this plant like a fly magnet. While I have not yet seen any fruits produced on my plant - the flowers are known to self, and can produce viable seed. Because the spontaneous production of fruits is relatively infrequent, I speculate that the local fly population is of the wrong size to effectively pollinate the flowers of this plant, and that some other agent (probably a much smaller fly) is probably responsible for the transfer of pollen in its native habitat.

   This is a notoriously difficult plant to maintain in cultivation. It is sensitive to over-watering, under-watering, cool growing conditions, inadequate light, excessive light, and seems to be rather selective about its potting mix as well. In relating their experiences in growing this plant, most growers, including those people who have managed to maintain it for years, invariably end their story with the phrase "and it turned to mush overnight".  I sometimes wonder if this plant is one of those that gardeners refer to as a "short lived perennial" in its native state - it seems to be so selective about its growing situation that I find it hard to believe that it is long lived - even in habitat.

   Clearly this plant is not a good choice for beginners - and for that matter, it may not be a good choice for many experienced growers either. It requires careful attention to detail. I have found that it is sensitive to any change, including such annual events as transitioning from dormancy to its growing period, or summer conditions to winter dormancy, with the attendant changes in temperature, exposure to sunlight, watering regimens, etc., as any of these changes may bring on the demise of this plant.

       In years past, I have grown this plant, and another close relative P. caput-viperae, and managed to maintain both for 2 years or so - better than average perhaps, but still nothing to brag about. I have recently acquired seedlings, and a mature plant, and hope to eventually propagate additional plants from these plants in the next year or so.

   There are several factors which I believe are necessary for long term success with this species.

       A quick drying potting medium that maintains lots of air pockets to keep aerobic conditions at the root zone. This medium should be fertile - not merely gritty. I have have good results with a blend of sifted mineral soil, Turface all-sport, and coir, but am currently using  Moo-nure with one of the seedlings with good results so far.

        The plants should be grown with a top dressing of pea gravel or some similar material to keep the lower stem dry, and to limit the spread of soil borne pathogens.

       While this plant will tolerate temperatures to the fifties and upper forties, I would recommend maintaining somewhat warmer temperatures during the winter dormancy (about 60 degrees and warmer), and keeping the plant warmer than 70 degrees during its growing period.

       I grow my plant outdoors during the summer months to benefit from increased exposure to daylight, increased temperatures and exposure to rain - which is arguably the best source of water for most plants. Given a fast draining potting medium, I have not yet lost a plant due to excessive rains, but I imagine that it is a definite possibility

These are good guidelines, but they will not guarantee success in and of themselves - the formula for long term success with this plant is still a bit of a mystery to me - I suspect that under anything short of a climate controlled greenhouse, long term survival of this plant may be a challenge to many growers.

   But don't let a challenge completely deter you - many people successfully grow and propagate this species -it can be done! The web is full of people who can offer you their advice on growing this plant, and for that matter, you can learn from the mistakes of others as well. If anyone has had good success in growing and propagating this species over a period of many years, I invite you to share your your techniques for success; I suspect that many others would be interested in such an exchange.

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