 
Henry Shaw
Cactus Society
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St. Louis, Missouri
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Along with other articles, columns and club updates, each monthly issue of the Henry Shaw Cactus Digest includes an article or two on members' favorite cactus and succulent species. The articles typically include photos and facts on the plants' natural origins and distribution, growing conditions, common and scientific names, care and cultivation tips, and helpful hints for encouraging flower production. Follow the links below this month's offering(s) to enjoy previous Plants of the Month.
May 2008 -- Astrophytum
By Eric Driskill
The genus Astrophytum is in the family Cactaceae and has four species. Its name is derived from the Greek "aster," star, and "phyton," plant. With the geometric shapes and patterns displayed by the various species, this is a very popular genus.
Unique to Astrophytum is the presence of small white flecks or flocking, which patterns and sometimes covers various species and cultivars. Perhaps this flocking aids water collection or protection from the sun. Regardless of its purpose, there is no doubt that it greatly adds to the popularity of the genus. Astrophytums have a geographical range from northern Mexico to southern Texas. Plants flower in summer over a period of several weeks.
One of the most popular astrophytums is A. asterias, also known as the sand dollar cactus, sea urchin cactus or star cactus. Historically, A. asterias ranged through Cameron, Hidalgo and Starr Counties in south Texas and the border states of Nuevo Leon and Tamaulipas in Mexico. Presently, this species is known from one population each in Starr County and Tamaulipas. It is listed as endangered in the U.S. Endangered Species Act and is included in Appendix I of CITES.
Fortunately, it is readily propagated by seed, and its rarity in the wild ensures that most plants encountered in nurseries are seed-grown. Plants are typically small, often 2 to 6 inches in diameter and usually 1 to 2 inches tall. Plants in habitat are very flat, barely rising above ground level. The cacti are gray-green, with numerous tufts of trichomes with very low ribs, flattened above and separated by sharp furrows.
The popularity of this species among growers and enthusiasts has ensured that a number of spectacular cultivars are available. One of the most popular cultivars is the Super Kabuto, a highly flocked white clone. For some spectacular examples of other cultivars, search any one of several Japanese or Thai nurseries.
Astrophytum capricorne has a fairly wide distribution in the Chihuahuan Desert in northern Mexico. Plants can reach 4 to 10 inches tall and 4 to 6 inches in diameter. They are green with a heavy coating of tufts of white trichomes and five to 10 brownish-black, twisted, flattened and somewhat flexible spines 1 to 3 inches long.
Astrophytum myriostigma, otherwise known as the bishop's cap, is cylindrical, 4 to 10 inches tall and 4 to 8 inches in diameter. Typically, there are five prominent, broadly triangular ribs. A. myriostigma is found in northern and central Mexico, primarily in the Chihuahuan Desert. A. myriostigma is variable in form. Numerous varieties, subspecies and forms have been described, but conservatives do not recognize them taxonomically.
The dark-green Astrophytum ornatum, which sometimes uses the alias monk's hood, is 12 to 40 inches tall and 6 to 12 inches in diameter, with scattered white tufts of trichomes. There is one central spine and five to 10 stout yellow radial spines that become brown with age. A. ornatum is found in central Mexico in Queretaro and Hidalgo.
One other astrophytum worthy of mention is A. myriostigma monstrose cv. Lotusland. This cultivar is almost always seen as a graft, but since offsets often produce roots, they can be rooted as well.
Most astrophytums require strong light and a light watering hand. Plants should do well in normal cactus potting mix, although some growers add limestone to remind them of the limestone formations in Mexico where the plants grow. Astrophytums enjoy a pH of 7, but you don't have to get that precise to grow them nicely. I would suggest growing them hard to keep them compact.
No cacti collection should be without at least one astrophytum. Due to its status, you can help the genus by only purchasing plants from a nursery that you know grows them from seed, or getting seed and starting them yourself. If you do grow them from seed, you stand a chance of finding a seedling with unique flocking not offered through any nursery.
May 2008 -- Aztekium ritteri
By Chris Deem
The 1920s were an interesting period in time. Young American girls drank gin, cut their hair short and danced with no knowledge of the Depression to come. In Egypt, the small tomb of a minor ruler revealed his short life, and his funerary goods stunned the world.
In Mexico, in the state of Nuevo Leon, stood the Sierra Madre Oriental Mountains, where a small discovery was made. Water pouring down the mountains had, over time, cut chasms in the stone. In one particular canyon, high on the rough mudstone walls, a most unusual species of cacti was found.
Growing in the broken sunlight, the small, hardy cacti defied gravity. Their roots held them fast in the cracks and crevices of the grumbling gypsum and weathering-resistant slate. They still grow there today.
To describe Aztekium ritteri is a difficult matter. They are tiny gray-green cacti with small taproots. Their small ribs have dirty white areoles and, here and there, a few small spines. The flowers are of a frail, exquisite nature. The colors are soft, pink and white.
Extremely slow growing, these cacti have a long lifespan. Fortunately, most cultivated plants are grafted and grow much faster than they do in habitat. Unfortunately, grafted plants stay greener and their aged gray cast is lost.
These cacti grow well in full sunlight. If the plants are growing on their own roots, water carefully. If they are grafted, water a bit more frequently. Aztekium ritteri is a unique plant that was discovered in a unique time.
May 2008 -- Crassula
By Eric Driskill
Crassula is a large genus in the family Crassulaceae containing around 200 species of succulent plants ranging in size from less than 1 inch in height to over 6 feet. In Latin, "crassus" means thick and aptly fits the stems and/or leaves of many species of Crassula.
Crassulas grow throughout the world, but the species that are used in gardening or by collectors are found almost exclusively in South Africa. Some species of Crassula are monocarpic and die after flowering. Typically crassulas are propagated by stem or leaf cuttings.
Many crassulas tolerate some frost, but excessive cold or heat will usually result in loss of foliage. The main pests you are likely to experience with crassulas are root and stem mealy bugs. Most Crassula species tolerate a wide range of light levels. However, the compact growth and leaf coloration seen in habitat require high light levels, preferably direct sunlight.
There are many crassulas worthy of adding to your collection. The most popular and well known by far is Crassula ovata, commonly known as the jade plant. C. ovata is from the Eastern Cape and can grow into a large shrub, which is a great bonsai specimen.
If you don't have room for C. ovata, you may want to consider C. agrentea, pygmae jade. With red-edged, bright-green leaves, it is half the size of C. ovata. These are easily trained, and when referring to this plant, I heard one grower say, "This one isn't your grandma's Jade plant."
One of my favorites is Crassula pyramidalis, which is a small, dichotomously branching plant up to 4 inches tall. C. pyramidalis has long, triangular green leaves densely arranged to form cylindrical columns.
Some of the most popular crassulas are C. ovata cultivars that include such gems as Gollum and Hobbit. The leaves of both remind us of some other world or something you might find under the sea. Popular hybrids include Morgans Beauty, C. mesembryanthemoides x C. falcate, and Buddha's Temple, which is a C. falcata x C. pyramidalis hybrid.
With so many crassulas from which to choose, with so many colors, sizes, shapes and geometric patterns, there is surely a crassula to suite anyone's taste. You could count several among your collection without sacrificing much of your precious space.
May 2008 -- Mammillaria bombycina
By Barbara Gardner
Mammillaria bombycina -- "cina" or silk, referring to the sheen on the spines -- is a reliable plant of cultivation from Coahuila, Mexico. It is at first a globular plant, becoming cylindrical in age and forming huge clumps. The stems, or cone-shaped tubercles, are up to 8 inches tall and 2 inches wide, with dense white wool in the axils, especially near the crown of the plant.
Its areoles have four hooked central spines and 30 to 40 whitish, thin, radial spines. The reddish-purple or pink flowers are about 2 to 3 inches long and wide -- they sort of look like silk straw flowers. They appear by day in mid-summer.
M. bombycina requires full sun and normal cactus compost. The minimum temperature to keep it in top condition is 50 degrees F. Propagation is normally by offsets, which should be removed as close to the parent plant as possible and dried for a week before planting.
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