Haworthia

Haworthia
Haworthia attenuata
Scientific classification
Kingdom:	Plantae
Clade:	Angiosperms
Clade:	Monocots
Order:	Asparagales
Family:	Asphodelaceae
Subfamily:	Asphodeloideae
Genus:	Haworthia Duval
Synonyms[1]
Apicra Willd. Catevala Medik. Kumaria Raf. Tulista Raf. × Apworthia Poelln.

Haworthia cymbiformis, showing the characteristic Haworthia flowers

Haworthia is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Swaziland, South Africa).^[1]

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. Horticulturally they are popular garden and container plants.

Description and characteristics

Haworthias are small succulent plants, forming rosettes of leaves from 3 cm (1.2 in) to exceptionally 30 cm (12 in) in diameter, depending on the species. These rosettes are usually stemless but in some species stems reach up to 50 cm (20 in). The inflorescences of some species may exceed 40 cm (16 in) in height. The plants can grow solitary or can be clump-forming. Most species have firm, tough, fleshy leaves, usually dark green in color, whereas others are softer and contain leaf windows with translucent panels through which sunlight can reach internal photosynthetic tissues. Their flowers are small, white and very similar between species. But their leaves show wide variations even within one species.

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 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 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. ^[2][3]

Subdivisions

The classification of the flowering plant subfamily Asphodeloideae is weak, and concepts of the genera are not well substantiated. Haworthia is 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. Currently, this relatively loose genus is subdivided into three very distinct groups, traditionally labelled as sub-genera:

• Haworthia, c. 42 spp. Typically green, stemless, soft-leaved species
• Hexangulares (or genus Haworthiopsis, G.D.Rowley), 18 spp. Hard-leaved and sometimes stemmed species
• Robustipedunculares (or genus Tulista, Raf.), 4 spp. Robust, hard-leaved species

Recent phylogenetic studies have demonstrated that the three sub-genera 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, it has been proposed that Hexangulares and Robustipedunculares be moved into new separate genera ("Haworthiopsis" and "Tulista" respectively).

Botanists had long noticed differences in the flowers the three sub-genera, 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.^[4][5]

Species

There are about 151 accepted species of Haworthia listed in the Plant List site produced in collaboration between the Royal Botanic Gardens, Kew and Missouri Botanical Garden. However, the actual number and identification of the species is not established; there are over forty species listed as "unresolved" for lack of sufficient information, and the full list reflects the difficulties of Haworthia taxonomy; it includes varieties and synonyms to a total of 966, even though it excludes various garden hybrids and cultivars.^[6] The following list includes only the fully accepted species in the Plant List.

A selection of Haworthias in cultivation

Cultivation

There is widespread special collector interest, and some species such as Haworthia attenuata and 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 overhands) and they are therefore healthiest in shade or semi-shade. Some species like Haworthia maxima 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. Rarer species may have more specific requirements.^[7]

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

Haworthia

• 
  Haworthia arachnoidea has numerous dark-green leaves, which have no translucent tips and bear a dense hairy web of spines.
• 
  Haworthia nortieri, from the far north-west of the Western Cape, has opaque leaves, covered in oval, pellucid spots.
• 
  Haworthia maculata, showing distinctive red-purple, spotted, normally turgid leaves, with tiny bristles on margins & keels.
• 
  The highly proliferous Haworthia reticulata bears tiny teeth and a reticulated pattern on its leaves.
• 
  Haworthia herbacea, showing distinctive yellow-green ("herbacea") colour, and spined margins & keels.
• 
  Haworthia pubescens co-occurs with H.herbacea but is very finely "pubescent" (covered in velvety fur)
• 
  Haworthia floribunda has relatively few dark, slender, twisted leaves with rounded ends.
• 
  Haworthia chloracantha forms clumps with slender, curved, yellow-green leaves
• 
  Haworthia variegata has thin, straight, erect leaves, with variegated spined margins.
• 
  Haworthia parksiana, the smallest Haworthia species.
• 
  Haworthia maraisii is a tiny, dark-coloured haworthia, with bristled, retused leaves.
• 
  Haworthia mirabilis has sharp-pointed, translucent leaf faces with marginal spines
• 
  Haworthia mirabilis var. badia has reddish-brown, attenuate leaves
• 
  Haworthia heidelbergensis possibly a form of H. mirabilis, with long, thin, bristle-tipped leaves, that are more outward spreading.
• 
  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.
• 
  Haworthia magnifica var. splendens is a particularly ornate variety with flecked leaves, prized by horticulturalists as "Haworthia splendens".
• 
  Haworthia magnifica var. acuminata has a lighter colour and more pointed, "acuminate" leaves
• 
  Haworthia magnifica var. atrofusca is a very dark, reddish-brown, rough-surfaced variety
• 
  Haworthia turgida is a compact, clumping, retuse haworthia, with swollen, "turgid", light-green leaves
• 
  Haworthia mutica has one or two lines and a pale, cloudy, mat surface on its compact, slightly rounded ("mutica") leaves
• 
  Haworthia groenwaldii is sometimes considered a smaller form of H.mutica, but has spots and a different flowering time
• 
  Haworthia retusa has a recognisable shiny leaf-face on its retuse leaves, and a light green colour
• 
  Haworthia pygmaea has flat, rough, scabrous or papillate leaf surfaces
• 
  "agenteo-maculosa" is a smoother variety of Haworthia pygmaea with silver spots ("argenteo maculosa")
• 
  Haworthia emelyae/picta has compact, bulging leaves which are often pink-flecked.
• 
  Haworthia bayeri has dark leaves with slightly rounded leaf tips.
• 
  Haworthia emelyae var. comptoniana is a large, lighter coloured form, with a clear reticulated pattern on the broad leaf faces
• 
  Haworthia springbokvlakensis has round, bulging, translucent leaf faces
• 
  Haworthia truncata ("Horse's teeth")
• 
  Haworthia wittebergensis showing its distinctive thin bristle-like leaves
• 
  Haworthia semivivadrys its leaves into a papery sheath in the heat of summer.
• 
  Haworthia lockwoodii drys its leaves into a papery sheath in the heat of summer.
• 
  Haworthia marumiana var. redii
• 
  Haworthia mucronata has translucent margins and keels on its soft, pointed ("mucronate") leaves.
• 
  Haworthia decipiens has light green, wide, flat, semi-translucent leaves, that have prodigious bristles on the margins (less so on the bottom leaf faces)
• 
  Haworthia cooperi (showing translucent "window" panels at the tips of its leaves)
• 
  An extreme rounded form of Haworthia cooperi
• 
  Haworthia cymbiformis has light green, even-coloured, boat-shaped leaves ("cymbiformis" = "boat shaped")
• 
  Haworthia blackburneae is a thin, grass-like species

Hexangulares (Haworthiopsis)

Coarctatae

Stemmed (caulescent) species:

• 
  Haworthia attenuata, probably the most commonly cultivated haworthia, has long attenuate leaves
• 
  The "glabrata" form of Haworthia attenuata has a more even brown colour, mostly without tubercles ("glabrous")
• 
  Haworthia fasciata has a lighter colour, and fibrous leaves with glabrous inner surfaces
• 
  Haworthia coarctata has small, smooth, rounded tubercles
• 
  Haworthia reinwardtii has larger, flatter, whiter tubercles, and is often more slender than H.coarctata.
• 
  Haworthia glauca has a blue ("glaucous") colour

Trifariae

Species with a three-way ("trifarious") leaf arrangement

• 
  Haworthia scabra is a stemless species with a rough scabrid leaf surface
• 
  Haworthia starkiana is a lighter, glabrous form of H.scabra
• 
  Haworthia nigra has a dark colour and concolourous tubercles
• 
  Haworthia viscosa has a lighter brown mat surface, and no tubercles
• 
  Haworthia pungens has hard, sharp ("pungent") leaf tips
• 
  Haworthia sordida has dark, dusty ("sordid") leaves with rounded tips
• 
  Haworthia longiana has long, thin, elongated leaves.

Venosae

Species with splayed leaves bearing vein-markings ("venose") on the upper leaf surface

• 
  Haworthia venosa has visible veins ("venosa") on its upper leaf surfaces
• 
  The tessellata subspecies of Haworthia venosa has more ornate, tessellated markings on its leaf-faces
• 
  The granulata subspecies of Haworthia venosa has compact little stems and granulate leaves
• 
  Haworthia limifolia has splayed leaves usually with raised lateral lines or wrinkles on the leaf surfaces
• 
  Haworthia koelmaniorum is an unusual species from far to the north of South Africa, which has scabrid, dark brown opaque leaves
• 
  Haworthia bruynsii has evolved a retuse shape, but is nonetheless a member of the hexangulares.

Robustipedunculares (Tulista)

• 
  Haworthia marginata has a mostly glabrous leaf surface, with clear white margins and keels.
• 
  Haworthia maxima is the largest haworthia, usually solitary, and heavily tubercled, with white & yellow-brown flowers
• 
  Haworthia minima is smaller and more proliferous/clumping than H.maxima, with more numerous, white, rounded tubercles and pink-white flowers.
• 
  Haworthia kingiana has a more yellow-green colour, and relatively fewer tubercles which are rounded and more flat to the surface of the leaf.

References

External links

Wikimedia Commons has media related to Haworthia.

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