Haworthia

Haworthia
Haworthia attenuata
Scientific classification
Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Xanthorrhoeaceae
Subfamily: Asphodeloideae
Genus: Haworthia
Duval
Synonyms[1]
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 Xanthorrhoeaceae, 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:

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]

Haworthia

Hexangulares (Haworthiopsis)

Robustipedunculares (Tulista)

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.

  1. Haworthia agnis Battista
  2. Haworthia akaonii M.Hayashi
  3. Haworthia albispina M.Hayashi
  4. Haworthia amethysta M.Hayashi
  5. Haworthia angustifolia Haw.
  6. Haworthia ao-onii M.Hayashi
  7. Haworthia aquamarina M.Hayashi
  8. Haworthia arabesqua M.Hayashi
  9. Haworthia arachnoidea (L.) Duval
  10. Haworthia aristata Haw.
  11. Haworthia attenuata (Haw.) Haw.
  12. Haworthia azurea M.Hayashi
  13. Haworthia bathylis M.Hayashi
  14. Haworthia bayeri J.D.Venter & S.A.Hammer
  15. Haworthia bella M.Hayashi
  16. Haworthia blackburniae W.F.Barker
  17. Haworthia bolusii Baker
  18. Haworthia borealis M.Hayashi
  19. Haworthia breueri M.Hayashi
  20. Haworthia bronkhorstii M.Hayashi
  21. Haworthia bruynsii M.B.Bayer
  22. Haworthia caerulea M.Hayashi & Breuer
  23. Haworthia caesia M.Hayashi
  24. Haworthia calva M.Hayashi
  25. Haworthia candida M.Hayashi
  26. Haworthia capillaris M.Hayashi
  27. Haworthia chloracantha Haw.
  28. Haworthia coarctata Haw.
  29. Haworthia compacta (Triebner) Breuer
  30. Haworthia cooperi Baker
  31. Haworthia crausii M.Hayashi
  32. Haworthia crinita M.Hayashi
  33. Haworthia crystallina M.Hayashi
  34. Haworthia cummingii Breuer & M.Hayashi
  35. Haworthia cymbiformis (Haw.) Duval
  36. Haworthia davidii (Breuer) M.Hayashi & Breuer
  37. Haworthia decipiens Poelln.
  38. Haworthia devriesii Breuer
  39. Haworthia diaphana M.Hayashi
  40. Haworthia diversicolor (Triebner & Poelln.) M.Hayashi
  41. Haworthia elizeae Breuer
  42. Haworthia emelyae Poelln.
  43. Haworthia emeralda M.Hayashi
  44. Haworthia eminens M.Hayashi
  45. Haworthia enigma M.Hayashi
  46. Haworthia esterhuizenii M.Hayashi
  47. Haworthia exilis M.Hayashi
  48. Haworthia fasciata (Willd.) Haw.
  49. Haworthia flavida M.Hayashi
  50. Haworthia floccosa M.Hayashi
  51. Haworthia florens M.Hayashi
  52. Haworthia floribunda Poelln.
  53. Haworthia fluffa M.Hayashi
  54. Haworthia foliosa Haw.
  55. Haworthia fukuyae M.Hayashi
  56. Haworthia glabrata (Salm-Dyck) Baker
  57. Haworthia glauca Baker
  58. Haworthia gracilis Poelln.
  59. Haworthia groenewaldii Breuer
  60. Haworthia hamata M.Hayashi
  61. Haworthia harryi M.Hayashi
  62. Haworthia hastata M.Hayashi
  63. Haworthia hayashii M.Hayashi
  64. Haworthia heidelbergensis G.G.Sm.
  65. Haworthia herbacea (Mill.) Stearn
  66. Haworthia hisui M.Hayashi
  67. Haworthia indigoa M.Hayashi
  68. Haworthia integra Poelln.
  69. Haworthia jadea M.Hayashi
  70. Haworthia jansenvillensis Breuer
  71. Haworthia jeffreis M.Hayashi
  72. Haworthia kemari M.Hayashi
  73. Haworthia kingiana Poelln.
  74. Haworthia koelmaniorum Oberm. & D.S.Hardy
  75. Haworthia lachnosa M.Hayashi
  76. Haworthia laeta M.Hayashi
  77. Haworthia latericia M.Hayashi
  78. Haworthia ligulata M.Hayashi
  79. Haworthia limifolia Marloth
  80. Haworthia lockwoodii Archibald
  81. Haworthia longiana Poelln.
  82. Haworthia maculata (Poelln.) M.B.Bayer
  83. Haworthia magnifica Poelln.
  84. Haworthia maraisii Poelln.
  85. Haworthia marginata (Lam.) Stearn
  86. Haworthia marmorata M.Hayashi
  87. Haworthia marumiana Uitewaal
  88. Haworthia marxii Gildenh.
  89. Haworthia maxima (L.) Duval
  90. Haworthia minima (Ait.) Haw.
  91. Haworthia minor (Aiton) Duval
  92. Haworthia mirabilis (Haw.) Haw.
  93. Haworthia mollis M.Hayashi
  94. Haworthia monticola Fourc.
  95. Haworthia mortonii Breuer
  96. Haworthia mucronata Haw.
  97. Haworthia mutica Haw.
  98. Haworthia nigra (Haw.) Baker
  99. Haworthia nigrata M.Hayashi
  100. Haworthia nortieri G.G.Sm.
  101. Haworthia oculata M.Hayashi
  102. Haworthia odetteae Breuer
  103. Haworthia ohkuwae M.Hayashi
  104. Haworthia opalina M.Hayashi
  105. Haworthia outeniquensis M.B.Bayer
  106. Haworthia pallidifolia (G.G.Sm.) M.Hayashi
  107. Haworthia parksiana Poelln.
  108. Haworthia pectinis M.Hayashi
  109. Haworthia pilosa M.Hayashi
  110. Haworthia pubescens M.B.Bayer
  111. Haworthia pulchella M.B.Bayer
  112. Haworthia pungens M.B.Bayer
  113. Haworthia pusilla M.Hayashi
  114. Haworthia pygmaea Poelln.
  115. Haworthia regalis M.Hayashi
  116. Haworthia regina M.Hayashi
  117. Haworthia reinwardtii (Salm-Dyck) Haw.
  118. Haworthia reticulata (Haw.) Haw.
  119. Haworthia retusa (L.) Duval
  120. Haworthia salina (Poelln.) M.Hayashi
  121. Haworthia sapphaia M.Hayashi
  122. Haworthia scabra Haw.
  123. Haworthia schoemanii M.Hayashi
  124. Haworthia scottii Breuer
  125. Haworthia semiviva (Poelln.) M.B.Bayer
  126. Haworthia serrata M.B.Bayer
  127. Haworthia sordida Haw.
  128. Haworthia sparsa M.Hayashi
  129. Haworthia springbokvlakensis C.L.Scott
  130. Haworthia subhamata M.Hayashi
  131. Haworthia subularis M.Hayashi
  132. Haworthia succinea M.Hayashi
  133. Haworthia tarkasia M.Hayashi
  134. Haworthia tauteae Archibald
  135. Haworthia teres M.Hayashi
  136. Haworthia tradouwensis Breuer
  137. Haworthia tretyrensis Breuer
  138. Haworthia tricolor (Breuer) M.Hayashi
  139. Haworthia truncata Schönland
  140. Haworthia truterorum Breuer & Marx
  141. Haworthia turgida Haw.
  142. Haworthia variegata L.Bolus
  143. Haworthia veltina M.Hayashi
  144. Haworthia venetia M.Hayashi
  145. Haworthia venosa (Lam.) Haw.
  146. Haworthia villosa M.Hayashi
  147. Haworthia violacea M.Hayashi
  148. Haworthia viscosa (L.) Haw.
  149. Haworthia vlokii M.B.Bayer
  150. Haworthia wittebergensis W.F.Barker
  151. Haworthia zantneriana Poelln.
  152. Haworthia zenigata M.Hayashi

Cultivation

A selection of Haworthias in 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.

References

  1. 1 2 Kew World Checklist of Selected Plant Families
  2. ↑ Stevens, P.F., Angiosperm Phylogeny Website: Asparagales: Asphodeloideae
  3. ↑ Bayer, B. (2012), Haworthia Update - Essays on Haworthia Vol. 7, Part 1.
  4. ↑ Manning, John; Boatwright, James S.; Daru, Barnabas H.; Maurin, Olivier; van der Bank, Michelle. A Molecular Phylogeny and Generic Classification of Asphodelaceae subfamily Alooideae: A Final Resolution of the Prickly Issue of Polyphyly in the Alooids? Systematic Botany, Volume 39, Number 1, March 2014, pp. 55-74
  5. ↑ http://www.haworthia.org.uk/haworthia.htm
  6. ↑ The Plant List (2010). Version 1. Published on the Internet; http://www.theplantlist.org/ (accessed December 2012).
  7. ↑ The cultivation of different Haworthia species

External links

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