Haworthia

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Haworthia
Haworthia glauca.jpg
Haworthia glauca
Scientific classification e
Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Xanthorrhoeaceae
Subfamily: Asphodeloideae
Genus: Haworthia
Duval
Haworthia cymbiformis, showing the characteristic Haworthia flowers

Haworthia is a genus of small succulent plants endemic to Southern Africa. Like the Aloes, they are members of the subfamily Asphodeloideae and they generally resemble miniature aloes, except in their flowers, which are characteristic in appearance. Horticulturally they are popular garden and container plants.

Overview and taxonomy[edit]

Haworthia is a genus within the family Xanthorrhoeaceae, subfamily Asphodeloideae.[1] They are small succulent plants, typically 4 cm (2 in) to 20 cm (8 in) high, depending on the species, though the inflorescences of some species may exceed 40 cm (16 in). solitary or clump-forming and endemic to South Africa. Most species have firm, tough leaves, usually dark green in color, whereas others are softer and are window plants 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.

Haworthia cooperi, a form of window plant with translucent panels at the tips of its leaves.

The classification of the flowering plant subfamily Asphodeloideae is weak and concepts of the genera are not well substantiated.[citation needed] Haworthia is similarly a weakly contrived genus consisting of three distinct groups: sub-genera Haworthia, Hexangularis, and Robustipedunculares.[citation needed] Related genera are Aloe, Gasteria and Astroloba and intergeneric hybrids are known.

The genus Haworthia is named after the botanist Adrian Hardy Haworth. B. Bayer recognized approximately 60 species in a review of the genus in 2012,[2] whereas other taxonomists are very much less conservative. Most species are endemic to South Africa, greatest diversity in the south-western Cape. Some do however extend to neighbouring territories in Swaziland, Namibia and Maputaland. The plants are small, forming rosettes of leaves from 3 cm (1.2 in) to exceptionally 30 cm (12 in) in diameter. These rosettes are usually stemless but in some species stems reach up to 50 cm (20 in).

Their flowers are small, white and very similar between species. There are differences in the flowers of the three sub-genera that botanists have curiously considered 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. Because of their horticultural interest, the taxonomy has been dominated by amateur collectors and the literature is rife with misunderstanding of what the taxa actually are or should be.[citation needed]

There is widespread special collector interest but some species such as Haworthia attenuata and Haworthia cymbiformis, are fairly common house and garden plants. 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.[citation needed]

Species[edit]

There are about 144 accepted species of Haworthia listed in the Plant List site [1] 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.[3] The following list includes only the fully accepted species in the Plant List.

References[edit]

  1. ^ Stevens, P.F. (2001 onwards), Angiosperm Phylogeny Website: Asparagales: Asphodeloideae 
  2. ^ Bayer, B. (2012), Haworthia Update - Essays on Haworthia Vol. 7, Part 1.
  3. ^ The Plant List (2010). Version 1. Published on the Internet; http://www.theplantlist.org/ (accessed December 2012).

External links[edit]