Haworthia Genus
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Login | Register General site search HOME ABOUT PLANTS OF THE WEEK VEGETATION OF SOUTH AFRICA INFORMATION LIBRARY CONTACT Haworthia genus Go to Plants of the Week Advanced Search Haworthia Duval Family: Asphodelaceae Common names: View other plants in this family View other plants in this genus QR code link These dwarf leaf succulents with their extremely variable compact rosettes of leaves with different colours, patterns and shapes, are extremely popular amongst succulent plant collectors. The genus is endemic to South Africa and centred in the Northern, Western and Eastern Cape Provinces, but is also found in the Orange Free State. Plants do well in cultivati and are perfect for container gardens and small rockeries. Their beautiful and variable features have made them popula hybridisation, which has given rise to many beautiful hybrids. Fig. 1: Leaf rosettes of Haworthia species. A: H. cymbiformis. B: H. decipiens. C: H. truncata. (Photos S.D. Gildenhuys) Description Haworthia is a genus of dwarf, leaf succulent plants. Evidence from molecular research on generic level relationships among the alooids, has resulted in the genus Haworthia being split into 3 segregate genera, which roughly correspond t the previously recognized subgenera. The species remaining in Haworthia are those that were previously included in Haworthia subgenus Haworthia. The 2 other subgenera are now treated as the genera Haworthiopsis (=Haworthia subgenus Hexangulares) and Tulista (=Haworthia subgenus Robustipedunculares). The genus Haworthia was named for Adrian Hardy Haworth (1768–1833), who was an authority on succulent plants during the early nineteenth century. Haworthia species are characterised by their usually stemless small rosettes of succulent leaves that are generally not a hard and tough as those of Haworthiopsis and Tulista. Leaf fibres are absent. There is great variation among Haworthia species, and even within a species or population, in terms of their leaf shape, size, colour and texture. Some species ofte divide or proliferate to form small to large clusters of numerous tightly packed rosettes, whereas a number of the other species always remain solitary. Plants produce unbranched inflorescences that are carried erectly, similarly to those in Haworthiopsis. Buds are held erectly during development and are disposed at an upward angle during flowering. Flowers are bilabiate (with a very distinct upper and lower lip), with a strongly curved tube, recurved tips, and are genera white or greyish white to dull pinkish white or greenish white, sometimes yellowish in the tube, often with a green, brownish or pinkish central vein on the tepals (flower leaves). In most species the flower tube narrows gradually to the flower stalk (pedicel) to form a short basal tube (flower tube not narrowing abruptly towards the pedicel as in Tulista), but some species the basal tube may have a distinct round swelling. The flower tube is triangular to rounded-triangular in cr section (not 6-sided as in Haworthiopsis and Tulista). Fig. 2: Flowers of Haworthia species. A: H. lockwoodii. B: H. retusa. C: H. tenera. (Photos S.D. Gildenhuys) Haworthia can mainly be divided into the summer-flowering and winter-flowering species. However, in some taxa there i some overlap into the other seasons. The 3-chambered fruit capsules split open when dry to reveal the angular, grey-coloured seeds. These fast- to slow- growing perennials have a relatively long lifespan and can survive for up to a few decades, especially in cultivation. Conservation Status There are several species of conservation concern in the genus Haworthia. At species level, 2 species, H. vlokii and H. wittebergensis, are considered to be Rare, whereas 1, H. blackburniae, is regarded as Near-threatened (NT). Threatened species include 4 species (H. floribunda, H. lockwoodii, H. outeniquensis and H. truncata) that have been assessed as Vulnerable (VU), 4 species (H. aristata, H. bayeri, H. chloracantha and H. springbokvlakensis) that are Endangered (EN) a 2 species (H. parksiana and H. pubescens) that are Critically Endangered (CR). While a total of 5 species (H. angustifolia, arachnoidea, H. nortieri, H. semiviva and H. zantneriana) are regarded as Least Concern (LC), and there are a staggering species that are Data Deficient based on Taxonomic grounds (DDT). For these DDT taxa we do not have sufficient information to make a proper conservation assessment, since the taxa are not well known, have only been collected a fe times, and/or we are unsure whether they should be recognised as distinct species. To date, none of the infraspecifc tax have been evaluated on the South African Red List. Main threats include habitat loss and degradation because of overgrazing, agricultural practices and expansion of agriculture, unsustainable firewood collecting that removes nursing/shelter plants, urban and road expansion, mining an quarrying activities, encroachment by alien invasive plants, and unscrupulous collecting for the specialised succulent pla trade. Distribution and habitat The genus Haworthia comprises a total of 38 species, of which no less than 25 are variously subdivided into varieties. T amounts to a total of 131 taxa that are currently recognised in Haworthia. Species concepts and circumscription in this group are often debated, and other researchers recognise a much larger number of taxa within this genus. The genus is endemic to South Africa, with all species occurring in the Northern, Western and/or Eastern Cape Provinces, with one species extending into the southern Free State. The Northern Cape harbours 6 taxa, the Western Cape 97 taxa of which are endemic to this Province, and the Eastern Cape is home to 42 taxa of which 33 are endemic. These plants occur in a variety of habitats ranging from flat grassy areas, to cliffs and high up in crevices of mountainous areas. The substrate they are found in varies considerably from sandy coastal soils to light clays. Annual rainfall varies fr approximately 200 mm in the area around Beaufort West, Westen Cape, to about 800 mm near East London, Eastern Cape. Precipitation could either be predominantly in winter, summer or rain throughout the year. Plants occur in a wide range of vegetation types, which may include Fynbos, Succulent Karoo, Nama Karoo, Grassland, and Albany Thicket. Fig. 3: Haworthia species occur in a variety of habitats. A: Habitat of H. cooperi in the Baviaanskloof, Eastern Cape. B: Habitat of H. cymbiformis near Port Elizabeth, Eastern Cape. C: Habitat of H. lockwoodii near Ezelsfontein, Western Cape D: Habitat of H. magnifica near Riversdale, Western Cape. (Photos S.D. Gildenhuys) Ecology The succulent nature of these plants enable them to survive long periods of drought. Plants often grow in areas with littl vegetation cover and are nestled in amongst rocks protecting them against fires. Despite growing in well-protected positions, the plants are occasionally predated on during droughts by tortoises, crickets and grasshoppers, and smaller rodents. A lot of suitable habitat have been destroyed by agricultural expansion for wheat and canola production in the Western Cape. Ostrich farming has caused the depletion of vegetation cover in areas like the Little Karoo. Urban expans also threatens Haworthia populations. As with the other haworthioids, the small flowers of Haworthia species are pollinated by proboscis flies or bees. Uses With their large variation in leaf shape and colouration, Haworthia species are very popular amongst succulent plant collectors. Plants hybridise easily, both interspecifically or intergenerically, and have produced a spectrum of beautiful hybrid plants. The species are widely cultivated and traded globally, and are often used in the horticultural trade for use small rock gardens or as pot plants. Growing Haworthia genus Because of their small size, species of Haworthia are well suited for container gardening. Some species can also be grow with success in outdoor rockeries in protected areas. They are generally hardy plants and does best in semi-shaded positions. However, some leaf colouration will only develop optimally under brighter light conditions. Fig. 4: Small angular seed of Haworthia. (Photo G. Marx) The species of Haworthia can be propagated by means of seed, offsets and leaf cuttings. Seed should be sown in spring and early summer, and covered with a very fine layer of sandy gravel or other suitable material. They should be placed i cool shady position. Seed should be kept moist during the first few weeks and should start to germinate in about 2 week After the first year, seedlings can be potted on into individual containers and will reach maturity in about 3 to 5 years, depending on the growing conditions. Offsets are easily removed by breaking or cutting them apart from the mother plant. Plants are best left to dry in a shady position for a few days, before being planted again. Plants can also be propagated by removing leaves from the mother plant with a blade; care should be taken to try and remove the leaves with a bit of stem tissue attached, to get the best results. The cut area can be treated with a rooting hormone and left to dry for a week or two before being planted with only the base below ground level. Species Haworthia arachnoidea (L.) Duval. Plants form a stemless rosette, with dense, incurving, light to dark green leaves. Rosettes vary between 60–120 mm in diameter and are usually solitary or occasionally forming small clusters. The keel and leaf margins bear long translucent spines that may be soft or become very sharp when dried (as in the var. scabrispina). This species is fairly widespread throughout the western parts of the Northern Cape, the far northern parts and interior of the Western Cape, and as far as Steytlerville and Jansenville in the Eastern Cape, South Africa. It usually grows on southern slopes under the shade of shrubs and ot plants in Fynbos vegetation in sandy, acidic, well-drained soil.