by Bruce Brethauer
Gymnocalycium is a genus of cactus which is native to South America. All species occur east of the Andes, and most are native to the southern half of the continent. Most species are small, seldom growing more than about 4 or 5 inches tall, and a few inches in diameter. While many species are typically solitary, or may produce a few offsets in time, a few species are highly caespitose, quickly producing dense clusters of many stems. The stems are divided by tuberculate ribs; one of the common names of this group of cacti, ("Chin Cactus") is based upon the curious chin-like tubercles which are typically produced just below the areoles in most species. One of the most diagnostic traits of this genus are its flower buds which are "naked", lacking hairs, or spines (the name "Gymnocalycium" translates "naked calyx"); the buds consist of a bundle of scale-like sepals and petals. Approximately 71 species are recognized (Edward Anderson, "The Cactus Family"), and many species are popular with cactus growers worldwide - indeed, the brightly colored stems of some cultivars of G. mihanovichii form the backbone of the grafted cactus industry: it can be argued that this species is one of the most commonly grown species of cactus (second perhaps to the various cultivars of the "Christmas Cactus")
Gymnocalycium bruchii is native to the province of Cordoba, Argentina, where it occurs at elevations from 1600 to abut 6500 feet. It is a miniature plant, producing stems to about 1.5 inches tall and to about 2.5 inches in diameter (although the plants which I have grown tended to have smaller stems - to about 1.25 inches in diameter). Each stem has about 12 shallow ribs, and unlike the greater number of Gymnocalycium species, does not produce the characteristic chin-shaped tubercles. The plants produce tufts of many clustering stems. In the plants which I have grown, these eventually amounted to several dozen stems, although I suspect that in venerable old specimens, these clusters will eventually proliferate to several hundred stems (the plant illustrated here has over 40 stems, and fits comfortably in a 4 inch pot). The spines are quite small, and bristle-like: spines typically emerge white or translucent, but will soon age to a more grayish coloration. Spine clusters typically have 2 or 3 short centrals, and about 12 re-curved radials, which practically lay against the stems surface: the illustrated spine cluster has no central spines.
Flowers are large in proportion to the size of the stems, measuring from about 1 to 2 inches long and across, and may vary from rose pink, through shell pink, to virtually white. The flowers open widely, and are shaped like a funnel when seen in profile. This is illustrated in the following link which shows a time lapse sequence of an opening flower. In my experience, G. bruchii flowers in spring, and is amongst the first of the cacti in my collection to flower. I have never had a plant flower twice in a season - I suspect that in habitat, there is a very short growing season, with a short rainy season in spring. The fruits are said to mature to a whitish or bluish coloration - but to date, none of the plants which I have grown have produced viable fruits, so I do not have a photograph of the fruits of this species.
Gymnocalycium bruchii makes an excellent houseplant: its compact size, with tight mounding clusters of stems looks especially good in a bonsai pot or a small dish garden. Even a good sized cluster will fit comfortably in a small pot, fitting nicely on a sill or small table. The short bristly spines are virtually incapable to causing injury, especially those plants which lack central spines altogether - a great asset in plants which may come into contact with inquisitive pets and children. This is an easy plant to grow, tolerating a wide variety of growing conditions: it is forgiving, and when it is happy, it is a reliable bloomer, producing a nice display fairly early in the season. It responds very well to my general guidelines on growing cacti and other succulents, but I thought it best to repeat a few guidelines here: This plant really grows best when it is moved outdoors to benefit from the spring and summer sun, temperatures and rain. if you have an area with particularly well draining soil, you might also try growing this species in the open ground through spring and summer, as I believe that no potting medium can compete with a well draining and fertile garden soil, but these plants should be dug up and re-potted at the end of the season. You may even try plunging the pots up to their rims in the open garden soil - this will make it easier to bring the plant back inside at the end of the season. Also, I have found that this plant really responds well to a COOL and dry winter dormancy, - kept dry, it will easily tolerate temperatures down to freezing - and may even tolerate brief periods of sub-freezing conditions without damage. Kept dry, I have seen plants survive temperatures to 0 degrees Fahrenheit, and some growers claim that it can survive temperatures down to -10 degrees, but temperatures down to the low 50's and 40's would probably be best for its winter dormancy. In winter, I have kept my plant sealed between a window, and plastic weather-stripping on a deep windowsill. On a cold winter night, this space can get down to the low 30's, and on some nights, frost may form on the window panes - but on a comparatively warm, sunny winter day, this same space may warm to more than 80 degrees. Plants are readily available, and are frequently included in selections of cactus at the various "Big Box" nurseries - although these are seldom identified by species. Various mail order nurseries offer this plant - I grew my first plants from seed purchased from Mesa Garden in Belen, New Mexico, but I have also seen plants offered from Bob Smoley's Gardenworld, and High Country Gardens.
My interest in Gymnocalycium bruchii began many years ago when I was testing many cactus species for their suitability in the hardy cactus garden: this species had a reputation of being very cold hardy. While some plants survived temperatures to below 0 degrees Fahrenheit in my garden, I ultimately had to abandon this species as a reliably hardy plant in Central Ohio: it does not tolerate our wet winter weather, and seems to have issues surviving long periods of uninterrupted sub freezing weather. But this is such an attractive plant, and has so many traits that I like, that I continue to come back to it, growing it as a houseplant, and trying an offset or two, every now and then, in my Columbus garden, just on the off hand chance that I may eventually find an extra hardy clone. It remains one of my favorite of the "indoor" cactus plants, it is so attractive, undemanding and reliable, that I suspect that it will be continue to be a favorite with many other growers.