by Bruce Brethauer
There are a good number of species from the “mesemb” family which are sometimes referred to as “Mimicry Plants” – these are plants which take on the features of the substrates in which they grow - including the size, shapes, textures, and coloration of the pebbles, stones and scree to be found in their habitat. In many instances, these plants so closely resemble the features of their substrate that they become virtually indistinguishable. The genera of Lithops and some species of Conophytum are frequently listed as mimic plants, but the list may also include members from the genera Argyroderma, Dinteranthus, Lapidaria, Pleiospilos and others. Most of these plants mimic pebbles which are small and generally fairly smooth, but there are a handful of plants which have taken on the rough appearance of the weathered limestone and scree beds in which they grow: these plants have developed a conspicuously warty appearance along their leaf tips - these are the species of Aloinopsis and Titanopsis - the "other" mimicry plants.
Titanopsis calcarea is a curious mat forming plant, which produces clusters of short rosettes, with odd flaring succulent leaves measuring to about an inch in length. The leaf tips, including the tips of the leaf's underside, bear numerous pebbly warts, which gives the leaves the appearance of being covered with limy deposits or incrustations of minute barnacles. The warts are typically of a whitish or pale grey coloration, but may also produce bluish, reddish, or ocher colors. The base color of the leaf may vary from grey/green to concrete to pale blue green depending upon the specific clone or location that the plants originated from (different populations may exhibit different colorations). Growing the plants in especially bright light is the best way to produce the best coloration - under lower light, these plants tend to become more greenish - this is the case of the illustrated plants - which were photographed in winter, after having been grown under lights for several months. The plants will eventually spread to 4 or more inches wide, but will always remain short - little more than an inch or so tall. Mature plants produce attractive yellow, daisy-like flowers measuring about an inch or so across. This species originates from the western region of Cape Province in South Africa, and grows on limestone outcrops and on limestone scree. In habitat, these plants are so well matched to the substrate, that even experienced plant hunters find it challenging to distinguish these plants from the stones amongst which they grow; it is only when they flower that they become easy to locate.
I first began growing Titanopsis calcarea more than 20 years ago, when I was making my first trial tests for succulents with exceptional cold hardiness. This species had been successfully grown outdoors at the Denver Botanical Gardens, and had a reputation for remarkable cold hardiness. I can vouch for the fact that some plants of this species, if kept absolutely dry through the winter months, can survive temperatures to below -20 degrees Fahrenheit, but when they are subjected to a typically wet Ohio winter, these same plants died at temperatures of about 20 degrees. Back then, my interest in succulents was largely restricted to those plants which I could confidently grow outdoors without winter protection, so for a time, I stopped growing this species. But I kept coming back to this plant - it has an appeal which is a bit hard to explain. Many of the traits which I find so appealing in this plant also make it something less than a stand-out in a larger collection of cacti and other succulents. First of all, this is a small plant - do not be confused by the name Titanopsis - this is not a reference to the Titans of mythology - and it is definitely not a Titanic: the name Titanopsis, roughly translated, means "resembling limestone". The coloration of this plant is typically subtle at best - what looks rather vibrant in macro photographs becomes more muted when seen at more typical viewing distances. Its warts are especially effective in helping this plant blend in - especially if you are in the habit of putting a top dressing of gravel on your pots of succulents. A plant in flower is quite attractive, but the flower colors of this plant are not quite as vibrant as they are in some of the other Mesembs: if you are growing succulents primarily for their exceptional flowers - this species may not be the perfect match for you. The real appeal of this plant is that through its many adaptations, it has become exceptionally good at hiding in plain sight. It is a plant which should be appreciated for the very traits that makes it hard to find in the first place. Its small size and compact growth habit makes this plant especially suitable for small dish gardens and bonsai pots: it is perfect for people with very limited growing space. It lacks spines and (to the best of my knowledge) this is a non toxic plant, making it suitable for households with inquisitive pets and children. The odd colors and textures of this plant give it a curious appeal - keep a magnifying glass handy to really appreciate these traits. While this plant is best grown in very bright light, it is tolerant of somewhat lower light levels (so given a bright windowsill - it will be reasonably happy). And of course, it is very tolerant of of drought - I find this to be a reasonably forgiving plant.
As a rule, I have found that this plant responds well to my General Guidelines for growing cactus and other succulents with a few important considerations. Different growers have claimed that this can be a rather finicky plant to maintain in collections - it has a reputation of being sensitive to excess water. Werner Rauh recommends that this plant should only be watered infrequently - no more than once a month during its growing season (from late winter through late fall), and not at all through the winter months. But this is not entirely my experience with this plant: I have found it to be reasonably tolerant of more frequent watering, provided that it is grown in an exceptionally porous medium. In the past, I have grown it in a mixture containing mostly limestone grit with a bit of some sifted garden compost, and am currently growing my plants in pure Moo-Nure - a medium which dries so quickly in the heat of summer, that I frequently water this plant weekly in July and August. Any planting of this species should always include a top dressing of limestone gravel. This will not only help to illuminate its adaptive mimicry, it will also provide the basic environment to which it is adapted. You may also opt to include a bit of ground limestone with its potting medium. I suspect that this plant does not appreciate peat or peat moss in its potting medium, and that the present paradigm of using acidified water to water succulents may not apply to this species. Despite the remarkable cold hardiness of this species, I do not recommend subjecting this plant to sub-freezing temperatures. Plants should be kept cooler and drier during its winter dormancy, but not necessarily any cooler than I recommend for other succulents. Be warned, this species is sensitive to perpetually wet soils, and will die if subjected to extended wet. As with many of the other mesembs, the demise of a plant can be quite rapid - especially if problems are not detected early - this can go from a perfectly healthy looking plant to total mush in the span of a few days. I also suspect that this species is not a very long lived plant - if you plan to maintain this plant for the long run, save seeds, and take cuttings and pot these up from time to time to insure that you always can re-establish your plant - just as a precaution.
While this species can be propagated from cuttings and divisions, it is probably best grown from seed, which are readily available through Mesa Garden, or from seeds produced on your own plants. Provided with moist and warm conditions, seeds will germinate in a week or two. Seedlings appreciate good air movement, and once they produce their first set of true leaves, should be permitted to go dry (briefly) between waterings. Growth can be fast, and plants can flower within their first year from seed. Established plants are frequently offered by a number of catalogs, including Mesa Garden, High Country Gardens, and Arrowhead Alpines.
This species is one of the great curiosities of the succulent world. Its dense rosettes of curiously warted leaves and cryptic coloration makes this species one of the great mimicry plants - helping it to blend in with the limestone in which it grows. It is a compact plant, fitting easily in a small bonsai pot, and can easily be maintained on a windowsill or narrow shelf. Its tolerance of extreme cold may make this plant especially suited to drafty areas, where winter temperatures may be a bit too cool for some of the more tropical succulents. It may not be for everyone, but for those growers who can appreciate a plant for being something of an ugly duckling, this could well become one of your favorites.