Haworthia

''Haworthia'' is a large genus of small succulent plants endemic to Southern Africa
(Mozambique, Namibia, Lesotho, Eswatini and South Africa).Kew World Checklist of Selected Plant Families
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Like the aloes, they are members of the subfamily Asphodeloideae and they generally resemble miniature aloes, except in their flowers, which are distinctive in appearance. They are popular garden and container plants.

Description and characteristics

''Haworthias'' are small succulent plants, forming rosettes of leaves from to exceptionally in diameter, depending on the species. These rosettes are usually stemless but in some species stems reach up to .
The inflorescences of some species may exceed in height.
The plants can grow solitary or can be clump-forming. Many species have firm, tough, fleshy leaves, usually dark green in colour, whereas others are softer and contain leaf windows with translucent panels through which sunlight can reach internal photosynthetic tissues. Their flowers are small, and generally white. Though they are very similar between species, flowers from the species in section Hexangulares generally have green striations and those from other species often have brown lines in the flowers. However, their leaves show wide variations even within one species.
Additionally, when the plants are stressed (e.g. deprived of water), their colours can change to reds and purples. Depriving them of nitrogen generally results in paler leaves.

Distribution

Most species are endemic to South Africa, with the greatest species diversity occurring in the south-western Cape. Some species do however extend into neighbouring territories, in Eswatini (formerly Swaziland), southern Namibia and southern Mozambique (Maputaland).

Naming and taxonomy

''Haworthia'' is a genus within the family Asphodelaceae, subfamily Asphodeloideae. The genus is named after the botanist Adrian Hardy Haworth. B. Bayer recognised 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.

Subdivisions

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 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.

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.

Species

Many species of ''Haworthia'' have been moved to ''Haworthiopsis'' and '' Tulista'', in particular since the last update of The Plant List (2013), which contains about 150 accepted species of ''Haworthia''. The actual number and identification of the species is 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 are listed below, excluding ''Haworthia kingiana'' and ''Haworthia minor'', placed in ''Tulista'' by other sources.

* '' Haworthia akaonii'' M.Hayashi – Western Cape Provinces
* '' Haworthia angustifolia'' Haw. – Southern Cape Provinces
* '' Haworthia ao-onii'' M.Hayashi – Cape Provinces
* '' Haworthia arachnoidea'' (L.) Duval – Southwestern Cape Provinces
* '' Haworthia aristata'' Haw. – Southern Cape Provinces
* '' Haworthia bayeri'' J.D.Venter & S.A.Hammer – Southwestern Cape Provinces
* '' Haworthia blackburniae'' W.F.Barker – Southwestern Cape Provinces
* '' Haworthia bolusii'' Baker – Southern central and southern Cape Provinces to Free State
* '' Haworthia caesia'' M.Hayashi – Western Cape Provinces
* '' Haworthia calva'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia chloracantha'' Haw. – Southwestern Cape Provinces
* '' Haworthia coarctata''
* '' Haworthia compacta'' (Triebner) Breuer – Cape Provinces
* '' Haworthia cooperi'' Baker – Southern Cape Provinces
* '' Haworthia cymbiformis'' (Haw.) Duval – Southern and southeastern Cape Provinces
* ''Haworthia decipiens'' Poelln. – Southern Cape Provinces
* '' Haworthia diaphana'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia elizeae'' Breuer – Western Cape Provinces
* '' Haworthia emelyae'' Poelln. – Southwestern Cape Provinces
* '' Haworthia fasciata''
* '' Haworthia floribunda'' Poelln. – Southwestern Cape Provinces
* '' Haworthia fukuyae'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia grenieri'' Breuer – Western Cape Provinces
* '' Haworthia heidelbergensis'' G.G.Sm. – Southwestern Cape Provinces
* '' Haworthia herbacea'' (Mill.) Stearn – Southwestern Cape Provinces
* '' Haworthia lockwoodii'' Archibald – Southwestern Cape Provinces
* '' Haworthia maculata'' (Poelln.) M.B.Bayer – Southwestern Cape Provinces
* ''Haworthia magnifica'' Poelln. – Southwestern Cape Provinces
* ''Haworthia maraisii'' Poelln. – Southwestern Cape Provinces
* '' Haworthia marumiana'' Uitewaal – Cape Provinces
* ''Haworthia mirabilis'' (Haw.) Haw. – Southwestern Cape Provinces
* '' Haworthia mollis'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia monticola'' Fourc. – Southwestern Cape Provinces
* ''Haworthia mucronata'' Haw. – Southwestern Cape Provinces
* '' Haworthia mutica'' Haw. – Southwestern Cape Provinces
* ''Haworthia nortieri'' G.G.Sm. – Southwestern Cape Provinces
* '' Haworthia outeniquensis'' M.B.Bayer – Southwestern Cape Provinces
* '' Haworthia parksiana'' Poelln. – Southwestern Cape Provinces
* '' Haworthia pubescens'' M.B.Bayer – Southwestern Cape Provinces
* '' Haworthia pulchella'' M.B.Bayer – Southwestern Cape Provinces
* '' Haworthia pygmaea'' Poelln. – Southwestern Cape Provinces
* '' Haworthia regina'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia reinwardtii''
* '' Haworthia reticulata'' (Haw.) Haw. – Southwestern Cape Provinces
* ''Haworthia retusa'' (L.) Duval – Southwestern Cape Provinces
* '' Haworthia rossouwii'' Poelln. – Cape Provinces
* '' Haworthia sapphaia'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia semiviva'' (Poelln.) M.B.Bayer – Cape Provinces
* '' Haworthia springbokvlakensis'' C.L.Scott – Southern Cape Provinces
* '' Haworthia subularis'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia tesselata''
* '' Haworthia transiens'' (Poelln.) M.Hayashi – Southern Cape Provinces
* ''Haworthia truncata'' Schönland – Southwestern Cape Provinces
* '' Haworthia turgida'' Haw. – Southwestern Cape Provinces
* '' Haworthia variegata'' L.Bolus – Southwestern Cape Provinces
* '' Haworthia veltina'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia villosa'' M.Hayashi – Eastern Cape Provinces
* '' Haworthia vlokii'' M.B.Bayer – Southwestern Cape Provinces
* '' Haworthia wittebergensis'' W.F.Barker – Southwestern Cape Provinces
* '' Haworthia zantneriana'' Poelln. – Southern Cape Provinces

Cultivation

There is widespread special collector interest, and some species such as '' Haworthia cymbiformis'' are fairly common house and garden plants.

Almost all ''Haworthia'' species are naturally adapted for semi-shade conditions (in habitat they tend to grow under bushes or rock overhangs) and they are therefore healthiest in shade or semi-shade. Some species like '' Haworthia pumila'' and ''Haworthia truncata'' can be adapted to tolerate full-sun however.

All ''Haworthia'' species favour extremely well-drained soil (in habitat they tend to grow in poor sands, in rocky areas). Watering depends on the species (winter or summer rainfall) but most of the common species are tolerant of a variety of watering routines. Over-watering can cause the roots to rot. Rarer species may have more specific requirements. All haworthias are sensitive to frost, and they are rated as winter hardy to USDA zone 10.

''Haworthia'' species reproduce both through seed and through budding, or offsets. Certain species or clones may be more successful or rapid in offset production, and these pups are easily removed to yield new plants once a substantial root system has developed on the offshoot. Less reliably, the plants may also be propagated through leaf cuttings, and in some instances, through tissue culture.

Gallery for identification

Image:Haworthia arachnoidea - cobweb aloe.jpg, '' Haworthia arachnoidea'' has numerous dark-green leaves, which have no translucent tips and bear a dense hairy web of spines.
File:Haworthia nortieri - MBB arizona.jpg, ''Haworthia nortieri'', from the far north-west of the Western Cape, has opaque leaves, covered in oval, pellucid spots.
File:Haworthia maculata - rawsonville 1.jpg, '' Haworthia maculata'', showing distinctive red-purple, spotted, normally turgid leaves, with tiny bristles on margins & keels.
File:Haworthia reticulata - Cape Town 6.jpg, The highly proliferous '' Haworthia reticulata'' bears tiny teeth and a reticulated pattern on its leaves.
File:Haworthia herbaceae var herbaceae - CT 6.jpg, '' Haworthia herbacea'', showing distinctive yellow-green (''"herbacea"'') colour, and spined margins & keels.
File:Haworthia pubescens - MBB Sandberg - Copy.jpg, '' Haworthia pubescens'' co-occurs with ''H.herbacea'' but is very finely "pubescent" (covered in velvety fur)
File:Haworthia floribunda MBB Appelbos.jpg, '' Haworthia floribunda'' has relatively few dark, slender, twisted leaves with rounded ends.
File:Haworthia chloracantha var chloracantha - Cape Town 6.jpg, '' Haworthia chloracantha'' forms clumps with slender, curved, yellow-green leaves
File:5 Haworthia variegata MBB Diepkloof.jpg, '' Haworthia variegata'' has thin, straight, erect leaves, with variegated spined margins.
File:Haworthia maraisii Aston South Africa 1.jpg, ''Haworthia maraisii'' is a tiny, dark-coloured haworthia, with bristled, retused leaves.
File:Haworthia parksiana - Acilliers South Africa.jpg, '' Haworthia parksiana'', the smallest Haworthia species.
File:5 Haworthia mirabilis - MBB Uitkyk.jpg, ''Haworthia mirabilis'' has sharp-pointed, translucent leaf faces with marginal spines
File:Haworthia mirabilis badia MBB 2 Napier.jpg, ''Haworthia mirabilis'' var. ''badia'' has reddish-brown, attenuate leaves
File:Haworthia heidelbergensis var heidelbergensis 5.jpg, '' Haworthia heidelbergensis'' possibly a form of ''H. mirabilis'', with long, thin, bristle-tipped leaves, that are more outward spreading.
File:5 Haworthia mirabilis magnifica - MBB type Frehse Reserve Riversdale c.jpg, ''Haworthia magnifica'' is sometimes considered to be a form of ''H. mirabilis''. It is distinguished by its flowers, but usually has dark, lined, triangular, scabrid leaf-faces.
File:Xanthorrhoeaceae - Haworthia magnifica var. splendens.JPG, '' Haworthia magnifica var. splendens'' is a particularly ornate variety with flecked leaves, prized by horticulturalists as ''"Haworthia splendens"''.
File:Haworthia magnifica var acuminata - MBB Vleesbaai 2.jpg, ''Haworthia magnifica'' var. ''acuminata'' has a lighter colour and more pointed, "acuminate" leaves
File:Haworthia magnifica var atrofusca - Basryhoogte MBB.jpg, ''Haworthia magnifica'' var. ''atrofusca'' is a very dark, reddish-brown, rough-surfaced variety
File:1 Haworthia turgida var turgida - Kirstenbosch.jpg, '' Haworthia turgida'' is a compact, clumping, retuse haworthia, with swollen, "turgid", light-green leaves
File:Haworthia mutica - stellenbosch 1.jpg, '' Haworthia mutica'' has one or two lines and a pale, cloudy, mat surface on its compact, slightly rounded ("mutica") leaves
File:2 Haworthia retusa - Acilliers - RSA 1.jpg, ''Haworthia retusa'' has a recognisable shiny leaf-face on its retuse leaves, and a light green colour
File:1 Haworthia pygmaea in cultivation a.jpg, '' Haworthia pygmaea'' has flat, rough, scabrous or papillate leaf surfaces
File:Haworthia pygmaea var argenteo maculosa - MBB Mossgas 1.jpg, '' "agenteo-maculosa"'' is a smoother variety of '' Haworthia pygmaea'' with silver spots ("argenteo maculosa")
File:Haworthia emelyae 1.jpg, '' Haworthia emelyae'' has compact, bulging leaves which are often pink-flecked.
File:Haworthia bayeri in habitat South Africa 2.jpg, '' Haworthia bayeri'' has dark leaves with slightly rounded leaf tips.
File:Haworthia emelyae v. comptoniana yc.jpg, ''Haworthia emelyae'' var. ''comptoniana'' is a large, lighter coloured form, with a clear reticulated pattern on the broad leaf faces
File:Juvenile Haworthia springbokvlakensis in cultivation.jpg, '' Haworthia springbokvlakensis'' has round, bulging, translucent leaf faces
File:Haworthia truncata 001.JPG, ''Haworthia truncata'' ("Horse's teeth")
File:Haworthia wittebergensis 3.jpg, '' Haworthia wittebergensis'' showing its distinctive thin bristle-like leaves
File:Winterbourne - Haworthia Semiviva (6120430747).jpg, '' Haworthia semiviva'' drys its leaves into a papery sheath in the heat of summer.
File:Haworthia lockwoodii (2-2) (4875874684).jpg, '' Haworthia lockwoodii'' drys its leaves into a papery sheath in the heat of summer.
File:5 Haworthia marumiana redii MBB.jpg, '' Haworthia marumiana'' var. ''redii''
File:1 Haworthia mucronata var mucronata - MBB barrydale.jpg, ''Haworthia mucronata'' has translucent margins and keels on its soft, pointed (''"mucronate"'') leaves.
File:1 Haworthia decipiens - Prince Albert a.jpg, ''Haworthia decipiens'' has light green, wide, flat, semi-translucent leaves, that have prodigious bristles on the margins (less so on the bottom leaf faces)
File:1 Haworthia cooperi - Kirstenbosch.jpg, '' Haworthia cooperi'' (showing translucent "window" panels at the tips of its leaves)
File:Haworthia cooperi - Tower Hill Botanic Garden.JPG, An extreme rounded form of '' Haworthia cooperi''
File:Haworthia cymbiformis - SBG 8.jpg, '' Haworthia cymbiformis'' has light green, even-coloured, boat-shaped leaves (''"cymbiformis"'' = ''"boat shaped"'')
File:Haworthia blackburneae var blackburneae - Stellenbosch.jpg, '' Haworthia blackburneae'' is a thin, grass-like species

References

External links

Haworthia (Ingo Breuer)Haworthia (Jakub Jilemicky)Asphodelaceae Anonymous (Lawrence Loucka)Haworthia Society Haworthia Updates (M.B.Bayer)

{{Taxonbar, from=Q133983

Flora of Southern Africa
Asphodelaceae genera