| Haworthia 1
It feels somewhat presumptuous to attempt to do justice to the genus Haworthia in a column (or even two), but nonetheless I’m going to take a crack at providing a quick overview and survey of the plants. At least two journals devoted solely to these popular, generally small and easy manageable succulent plants have appeared over the years, as well as a number of books. Haworthias achieved their first popularity in the early nineteenth century, and have maintained it ever since. Even after all this time, new species and varieties keep being discovered, as many haworthias have mastered the art of staying hidden from prying eyes and wandering, plant-munching mouths.
Their long history in cultivation has led to years of confusion over the identities of Haworthia species. The plants readily hybridize (although in the wild, even growing sympatrically—occupying the same territory—species cross only rarely), and over the years many garden hybrids were described as valid species. Moreover, since cultivated plants may diverge wildly from their normal, wild forms under conditions of richer soil, less light (or more light…) and so forth, the identification of uncertain cultivated material with actual species often was pretty dubious. As a result, valid names sometimes became firmly identified with hybrid forms, and these plants might be passed along for generations with no realization that they weren’t species at all. Over the last thirty or forty years, a small number of dedicated (even fanatical) field botanists have done much to rectify this situation. Unfortunately, they have not always agreed among themselves on what was what, leading for a while to a whole new level of confusion. And last, but not least, the very fact that Haworthia have been popular and collected for a long time has led to the creation of far more species and variety names than have ever really existed.
Today Haworthia taxonomy has calmed down to a certain degree, but there are still disagreements and controversies surrounding some species and their exact relationship with others. The work of people such as M. B. Bayer and C.L. Scott has done much to make some sort of sense out of the genus.
So what exactly are these popular and confusing plants? Close relatives of Aloe and Gasteria, Haworthia were once included with them in an over-expanded Lily family. Now, depending on who’s talking, they’re either in the Asphodelaceae or Aloeaceae, new families carved out of the Liliaceae. Most Haworthia are small, rosette forming plants, usually with fleshy green leaves, and they produce relatively long flower stalks that bear small, tubular, somewhat asymmetrical flowers, basically white, but sometimes with green, pink, or brownish lines. Slightly more than sixty species are generally currently acknowledged (out of several hundred names), with close to twice that many varieties. It’s widely accepted that the plants fall into three reasonably easily defined subgenera (with exceptions…), but within each of the subgenera determination of species can still be fraught with difficulty.
Most people will recognize some of these light green, often rather translucent, little rosettes, or short columns of darker green leaves marked with white tubercles as common inhabitants of dish gardens and window sills. Some forms thrive with little care in gardens, given partial shade and not too much water. People familiar with this generalized, easily grown, rapid-multiplying concept of Haworthia plants may be astounded at the high prices collectors will pay for rare specimens, and almost unbelieving at the slow rate of growth of some of these rare forms. As I indicated, many of the most widely distributed haworthias are really garden hybrids, prolific and almost indestructible. But now let’s talk about some of the other kind.
The central subgenus of Haworthia, also called Haworthia, with about two thirds of the species, consists of mostly low-growing, stemless rosette-forming plants. There are several basic growth forms that I’ll summarize—remember these are not necessarily groupings of closely related species. The first consists of plants with generally pale-green, somewhat translucent, usually rather soft leaves. The best known of these is Haworthiacymbiformis, with leaves shaped (its name means “boat-form”) something like little rowboats, curving on the outer surface, concave on the inner, and coming to a little point. Typical H. cymbiformis produces offsets rapidly, but some forms, with larger, more triangular leaves (formerly known as H. planifolia), may remain solitary for many years. Other varieties of H. cymbiformis may be smaller, with more curving leaves, or may even form long, pendent (hanging downward) stems (varieties incurvula and ramosa). Other species that more or less share this growth form include H. cooperi, H. marumiana, H. mucronata, and to a certain degree, H. reticulata. Most of these plants enjoy a considerable degree of shade, growing well under bushes or on hillsides away from the sun, but certain forms can withstand considerably more light. In the wild, the more or less transparent, egg-shaped leaf tips of some of these die back, leaving a flattened, clear surface completely flush with the soil. The outer leaves of some other species that resemble these plants, such as H. lockwoodii, dry up almost completely during the dry parts of the year, and the plant during this dormancy looks almost like a little onion.
The windowed leaf-tip of some of the cymbiformis-type species also occurs in a second group of haworthias, those centering around Haworthia retusa. This group of plants, with recurved leaf tips (“retuse”) that often form quite transparent windows, include many of the most popular and sought after species. Haworthia retusa itself is most often represented in cultivation by a rapidly offsetting, medium sized, rather chunky plant with firm, glassy green leaves. Unfortunately, this form probably is a hybrid, as the true species has only come into general cultivation in the last fifteen years or so. Although generally similar to its inaccurately named doppelganger, the true species may grow considerably larger (to over six inches in diameter), and is much shyer about producing offsets. It often has attractive silvery-gray lines along the upper surfaces of its leaves. These pretty marking lead us to a whole array of nicely decorated plants, including the inappropriately named Haworthiapygmaea, the many distinct varieties of H. mirabilis and H. magnifica, and the variable and beautiful H, emelyae and H. bayeri. If grown properly, the nicest forms of these species resemble little sculptures of stained glass more than they do ordinary green plants. H. mirabilis var. badia, H. pygmaea var. argenteo-maculosa (“silver spotted”), H. magnifica var. atrofusca, H. emelyae, and above all, H. magnifica var. splendens, all turn extraordinary colors if treated right: purple, turquoise, pink, gold, and may be streaked and dotted with white, gold and silver as well. In habitat, many of these plants grow flush with the soil, and their baroque coloring actually serves to camouflage them amid the pebbles and sparse bushes. Their transparent leaf tips and tops act as windows that let light into their interior so they can photosynthesize from inside, without having to expose more of the their mass to the potential threats of the great outdoors. In contrast to most of the H. cymbiformis types, many of these plants are slow to offset, and some never do, reproducing themselves only by seed.
Perhaps the best of these plants at concealing itself, and one that frequently provokes the most interest, is Haworthiatruncata, and its variety (often considered a distinct species), maughani. Rather than form a rosette, the leaves of H. truncata grows in two ranks, resulting in a shape like an old fashioned fan. The windowed, completely flat leaf tips, that look as if they’d been cut off with a knife, remain flush with the soil in the wild. Though the closely related H. maughani forms a rosette, it too has strange, angularly faceted, cut-off seeming leaf tips, and looks more like a tiny model of a modern sculpture than it does a plant.
A third group of Haworthia shares a growth form that makes them resemble silvery little spherical spider webs. These haworthias are perhaps best represented by the various varieties and forms of the appropriately named Haworthiaarachnoidea. As currently understood the species includes seven varieties, all of which have at one time or another been considered separate species. These plants, and the very similar H. bolusii, from farther east, form smallish rosettes of leaves, but each of their narrow leaves is densely edged with translucent bristles, so much so that the shimmering bristles dominate the appearance of the entire plant. A number of other Haworthia share this general look, including H. nortieri, H. decipiens, some varieties of H. herbacea, and H. semiviva.
A fourth, rather catch-all group of plants includes several small species with narrow, opaque green leaves. Haworthia parksiana, with almost black leaves, forms very slow growing rosettes no more than an inch across. On the other hand, the equally small rosettes of H. chloracantha var. denticulifera reproduce so rapidly that a single plant will multiply to fill a four inch pot in four or five years. The other varieties of H. chloracantha, larger and with broader leaves, also grow very easily, although not quite as rapidly. H. angustifolia, H. floribunda, the very rare H. pubescens, and the odd, long-leafed H. wittebergensis all share this general configuration, while the very variable H. gracilis includes forms that would fit here, as well as some that look more like the spider-web plants, and some like those centered around H. cymbiformis. These groups indicate nothing more than plants that look a certain way, and most of the more widely distributed species of Haworthia can vary tremendously in appearance across their range—the presence of bristles, windows and spots on leaves has very little significance in determining relationships between species, although it has a lot to do with determining which plants people consider desirable to grow and collect.
Although many of the faster growing, readily offsetting species in this subgenus are very easy to grow, a few words about their habitat and its effects on their growth requirements can’t hurt. Most members of the subgenus Haworthia grow in the western half of South Africa, whether along the coastal strip of the Western Cape Province, the semi-desert of the Little Karoo, the more intense desert of the Great Karoo, or the mountains and plains of the northwest part of the country. All these areas more-or-less share a general precipitation pattern of a summer dry season, and fall through spring rainfall. The easiest growing haworthias don’t need a specialized watering regime to do well, and watering them about once a week in spring, summer and fall, and about every two weeks in winter will keep them alive. A better choice, however, and one that’s almost mandatory for the more delicate species, is a partial summer dry period, with water about every two weeks, more frequent water in spring and fall (once a week), and again, water about every two weeks in winter. Keeping these plants too wet in summer frequently leads to a loss of their roots, and although the plants will regenerate, over time they will disappear.
A couple of species, such as Haworthianortieri, from the far west, need a somewhat stricter summer drought, and more careful watering in spring and fall, with water a bit more often in winter (every ten days or so, depending on the weather), while many of the spiderweb plants also might do better with water every ten days during their growing period, rather than once a week. For years I’ve given H. truncata and its var. maughani water only every two weeks during the growing season, and every three weeks or less during summer and winter. These plants, and other species with similarly massive tuberous roots, can be susceptible to rotting if kept too wet.
In regard to soil, haworthias aren’t particularly fussy, as long as the soil drains rapidly and has at least a bit of organic matter in it. Again, the easy growing species will do well in almost any mix while the more refractory ones will benefit from extra drainage and more specialized ingredients.
Light is the variable most often misapplied to haworthias. They all will survive in quite low light for succulent plants, and species such as H. cymbiformis, which grow in the shade of dense bushes in the wild, will do well under such conditions, but, in my opinion at least, most people don’t give haworthias enough light. Inadequate light for the species in the retusa group, and those cooperi and cymbiformis types that develop windowed tips to their leaves, will simply never display the brilliant colors and patterns that mark them in the wild. My rule of thumb is to give the plants as much light as they can take without burning (and the irregular, discolored splotches of leaf-burn look nothing like the symmetrically patterned bands and lines of color that define well grown plants). Still, most haworthias will be perfectly happy in an east-facing window that gets good morning light with some sun, while in a south or west facing window they probably should get a bit of shade from hotter sunlight.
We always have some Haworthia to sell, and have a number of very good species to offer. For years the Garden’s collection of accurately named species was limited, but in the last few years it has improved a lot, and we now have a good assortment of many of the most interesting species.
Next month I’ll discuss the other two subgenera, not quite as popular with growers, but consisting of a good number of very interesting plants all the same.
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