Haworthia haw-thor-ia is a large genus of small succulent plants endemic to Southern Africa. Some species do however extend into neighboring territories, in Swaziland, southern Namibia, and southern Mozambique.
The genus is named after the botanist Adrian Hardy Haworth. B. Bayer recognized approximately 60 species in a review of the genus in 2012, whereas other taxonomists are very much less conservative. Related genera are Aloe, Gasteria, and Astroloba and intergeneric hybrids are known.
Like the aloes, they belong to the subfamily Asphodeloideae. The classification of the flowering plant subfamily Asphodeloideae is weak, and concepts of the genera are not well substantiated.
Haworthia has been a similarly a weakly contrived genus. Because of their horticultural interest, its taxonomy has been dominated by amateur collectors, and the literature is rife with a misunderstanding of what the taxa actually are or should be.
Recent phylogenetic studies have demonstrated that the traditional divisions of the genus are actually relatively unrelated.
Hexangulares was shown to be a sister-group of genus Gasteria, Robustipedunculares more closely related to genus Astroloba, and Haworthia as an out-group related to Aloe. In recognition of the polyphyletic nature of the genus, Haworthiopsis and Tulista have been split off.
Haworthias were included in the genus Aloe before being promoted to a new genus in the Asphodelaceae family in the early 1800s. In the 2010s, genetic studies further divided the former genus Haworthia into three genera: Haworthia (42 species), Haworthiopsis (18 species) and Tulista (4 species).
Botanists had long noticed differences in the flowers the three subgenera, but had previously considered those differences to be inconsequential, although the differences between species in the same subgenus definitely are. The roots, leaves, and rosettes do demonstrate some generic differences while wide variations occur even within one species.
Many species of Haworthia have been moved to Haworthiopsis and Tulista, in particular since the last update of The Plant List, which contains about 150 accepted species of Haworthia.
The actual number and identification of the species are not well established; many species are listed as “unresolved” for lack of sufficient information, and the full list reflects the difficulties of Haworthia taxonomy, including many varieties and synonyms. The World Checklist of Selected Plant Families has been updated to exclude the species now in Haworthiopsis and Tulista.
The species it accepts as of February 2018 exclude Haworthia kingiana and Haworthia minor, placed in Tulista by other sources. Those are the following with some purhasing links added:
- Haworthia akaonii – Western Cape Provinces
- Haworthia angustifolia – Southern Cape Provinces
- Haworthia ao-onii – Cape Provinces
- Haworthia arachnoidea – Southwestern Cape Provinces
- Haworthia aristata . – Southern Cape Provinces
- Haworthia bayeri – Southwestern Cape Provinces
- Haworthia blackburniae – Southwestern Cape Provinces
- Haworthia bolusii – Southern central and southern Cape Provinces to Free State
- Haworthia caesia – Western Cape Provinces
- Haworthia calva – Eastern Cape Provinces
- Haworthia chloracantha – Southwestern Cape Provinces
- Haworthia compacta – Cape Provinces
- Haworthia cooperi – Southern Cape Provinces
- Haworthia cymbiformis – Southern and southeastern Cape Provinces
- Haworthia decipiens – Southern Cape Provinces
- Haworthia diaphana – Eastern Cape Provinces
- Haworthia elizeae – Western Cape Provinces
- Haworthia emelyae – Southwestern Cape Provinces
- Haworthia floribunda . – Southwestern Cape Provinces
- Haworthia fukuyae – Eastern Cape Provinces
- Haworthia grenieri – Western Cape Provinces
- Haworthia heidelbergensis – Southwestern Cape Provinces
- Haworthia herbacea– Southwestern Cape Provinces
- Haworthiopsis limifolia, formerly Haworthia limifolia – South Africa
- Haworthia lockwoodii – Southwestern Cape Provinces
- Haworthia maculata – Southwestern Cape Provinces
- Haworthia magnifica – Southwestern Cape Provinces
- Haworthia maraisii . – Southwestern Cape Provinces
- Haworthia marumiana – Cape Provinces
- Haworthia mirabilis – Southwestern Cape Provinces
- Haworthia mollis.– Eastern Cape Provinces
- Haworthia monticola . – Southwestern Cape Provinces
- Haworthia mucronata . – Southwestern Cape Provinces
- Haworthia mutica – Southwestern Cape Provinces
- Haworthia nortieri – Southwestern Cape Provinces
- Haworthia outeniquensis – Southwestern Cape Provinces
- Haworthia parksiana – Southwestern Cape Provinces
- Haworthia pubescens – Southwestern Cape Provinces
- Haworthia pulchella – Southwestern Cape Provinces
- Haworthia pygmaea – Southwestern Cape Provinces
- Haworthia regina – Eastern Cape Provinces
- Haworthia reticulata – Southwestern Cape Provinces
- Haworthia retusa – Southwestern Cape Provinces
- Haworthia rossouwii – Cape Provinces
- Haworthia sapphaia – Eastern Cape Provinces
- Haworthia semiviva – Cape Provinces
- Haworthia springbokvlakensis – Southern Cape Provinces
- Haworthia subularis – Eastern Cape Provinces
- Haworthia transiens – Southern Cape Provinces
- Haworthia truncata Southwestern Cape Provinces
- Haworthia turgida – Southwestern Cape Provinces
- Haworthia variegata – Southwestern Cape Provinces
- Haworthia veltina – Eastern Cape Provinces
- Haworthia villosa – Eastern Cape Provinces
- Haworthia vlokii – Southwestern Cape Provinces
- Haworthia wittebergensis – Southwestern Cape Provinces
- Haworthia zantneriana – Southern Cape Provinces
Haworthias are easy to grow as long as you keep in mind that they are succulents, and require the appropriate light, temperature, soil, and water. Although it is possible to kill a Haworthia, they are generally forgiving of the occasional lapses of ideal care.
Light. The stereotypical image of cacti and other succulent plants is as desert inhabitants, living fully exposed in the hot, bright sun. Whereas large plants can survive such harsh conditions, many smaller succulents actually are found in the shade of rocks or shrubs.
Although some Haworthia species can be found in full, bright sun, many live in more protected spots and therefore are adapted to thrive in partial shade (though few look their best without at least some direct sun or bright light). This makes Haworthias well adapted to lower light conditions found in homes.
They probably do best in an east or west-facing window where they get a few hours of direct light daily, and bright indirect light through the remainder of the daylight hours. A south-facing window would also be acceptable but maybe too bright for some species unless the sun is lightly filtered through sheer curtains.
Haworthias do very well in sunrooms and greenhouses, though again many of them prefer to be located where they don’t get persistent direct sunlight, especially during the warmer part of the year. Haworthias grow very well under artificial lights, though they prefer more light intensity than provided by the standard fluorescent “grow lights.” A mixture of warm white and cool white bulbs gives both good light intensity and color balance.
The darker and more intense coloration and the very compact growth which many growers find most attractive are developed from brighter light conditions. In insufficient light, leaves will elongate and plants will lose the richness of their colors.
Haworthias make good accent plants on porch, patio, or deck and can be grown outdoors during frost-free periods. Be careful when you move plants outdoors. If they have spent the winter without much direct sunlight, don’t immediately put them into full sun outdoors or they may sunburn. Gradually move them into more direct light over a period of a few weeks.
Temperature. Some Haworthias can survive a few degrees of light frost for a short period, but it is best not to take chances. They do best in the temperature range of 75-90°F. But they can tolerate temperatures into the low 40s, especially if they do not have continuously wet soil, and they will survive high temperatures into the low 100s, especially if they are somewhat shaded and have good air movement.
Soil. Like most all succulent plants, Haworthias do not like their roots to remain wet for prolonged periods, so their soil mix should be well-drained. A good commercial potting soil should be mixed with equal amounts of drainage material. Several options exist, including perlite (available in garden stores), aquarium gravel, poultry grit (available at feed stores and agricultural supply stores), or horticultural pumice (available at better garden centers or through mail-order succulent nurseries).
Do not use sand as it is too fine and clogs the pores in the soil. If using a peat-based potting soil, remember that peat decomposes in a few years, resulting in unhealthy soil. As some Haworthias are slow-growing and can stay in the same pot for years, there may be a tendency to forget to repot into fresh soil, a practice that should be done every 2-3 years.
Watering. If the soil mix is well-drained, Haworthias can be watered weekly in the summer months; less frequently in the winter. The soil should dry between waterings. Prolonged wet soil, especially when it is cool, there is low light intensity, and/or the plants are not actively growing, can lead to root rot, a common problem with Haworthias. Symptoms of a weak or rotted root system include the stoppage of growth, reduction in plant or leaf size, or leaf shriveling.
Often though, root rot does not necessarily mean the plant will be lost. If the plant looks unhealthy, unpot it and inspect the roots. Remove any weak or decayed roots, even back to the stem of the plant. Allow the plant to lie out unpotted for a week, then repot into fresh soil and begin watering carefully until it is apparent that the roots have re-established and the plant has regained its health.
Remember that a healthy root system is the best method for removing excess soil moisture (through the transpiration process). Therefore, when repotting a plant, try to use a pot about the same volume as the root system. If the roots are diminished, or a larger pot is desired, just remember to water sparingly until the plants are reestablished.
It is difficult to generalize about the growing season of Haworthias. In nature, some come from winter rainfall areas and are winter growers, whereas others are from summer rainfall areas and are summer growers. For many species, the growing season is from late winter through spring (as the day length increases).
Containers. Haworthias can be grown in virtually any type of container, including plastic pots, ceramic, or terra cotta. Terra cotta pots breath and release soil moisture faster than ceramic or plastic. Shallow pots are generally better than deep pots, but some species have heavy, thick roots that ask for a deeper pot. Be sure that your containers have drain holes, and, if you use saucers, be sure that you empty any standing water promptly.
Also, remember to use a pot that properly matches the size of the root system. Many Haworthias freely offset and eventually form clusters much larger than the individual plant. It is better to repot periodically as needed to provide additional space for the expanding plant rather than put a small plant in a large pot expecting the plant to eventually fill the container.
Propagation. Vegetative propagation, especially by taking cuttings, is the quickest and most common method of propagating Haworthias. The majority of species cluster from the base; the new young plants are often referred to as offsets or “pups”. In many cases, as soon as the new young plants are formed by the parent plant, they develop roots.
In some species, as soon as the new plant becomes well established, the original contact with the parent plant is broken; when the clump is unpotted, the individual plants fall away from each other. In other species, the attachment to the parent plant may remain; this can easily be broken or cut to separate the plants.
If you create a subsoil wound during the separation process the plants should be allowed to air-heal for a few days before repotting to avoid the possibility of pathogenic organisms moving from the soil into the fresh wound.
As well as all the other positive traits about the Haworthia, another bonus is that it’s not poisonous to people, cats or dogs.
Haworthiopsis limifolia, formerly Haworthia limifolia, is often used by traditional healers as a spiritual remedy to ward off evil as well as a treatment as blood purifiers and cures against coughs, skin rashes, sunburns, burns, etc. H. limifolia exhibits similar morphological characteristics as Aloe species.
Validation of the use of H. limifolia crude extracts from the leaves was successful against five Gram-positive and four Gram-negative bacteria.
Extracts from the leaves also exhibited antimicrobial activities in all treatments against the selected bacterial and fungal strains.
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