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Disa (plant)

Article Discussion

Template:Short description Template:Automatic taxobox

Disa is a genus of flowering plants in the family Orchidaceae. It comprises about 182 species.<ref name=chase2015>Template:Cite journal</ref><ref name="tammy">Kew World Checklist of Selected Plant Families</ref> Most of the species are indigenous to tropical and southern Africa, with a few more in the Arabian Peninsula, Madagascar, and Réunion.<ref name=linder1999>Hans Peter Linder and Hubert Kurzweil. 1999. Orchids of Southern Africa. 504 pages. A. A. Balkema. Template:ISBN.</ref> Disa bracteata is naturalised in Western Australia, where the local name is "African weed-orchid."<ref>Weeds Australia, Weed Identification, African weed-orchid, Disa bracteata Template:Webarchive</ref>

The genus Disa was named by P.J. Bergius in 1767.<ref name="ipni">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=bergius1767>Peter Jonas Bergius. 1767. Descriptiones Plantarum ex Capite Bonae Spei: 348. (See External links below).</ref> It was named after Disa, the heroine of a Swedish legend.<ref name="quattrocchiII">Umberto Quattrocchi. 2000. CRC World Dictionary of Plant Names volume II. CRC Press: Boca Raton; New York; Washington,DC;, USA. London, UK. Template:ISBN (vol. II). (see External links below).</ref>

DescriptionEdit

The plants grow from a fleshy tuberous root which is a source of maltodextrins which are used as a sugar substitute. Some species attain a height of 90 cm. The flowers are solitary or arranged in racemes. The petals and the lip are small. The flowers consist essentially of the sepals. The flowers range in color from very light to dark red.

PollinationEdit

Disa exhibits a variety of pollination syndromes. Each species of Disa usually has a single species as pollinator and nearly every available pollinating insect is employed by some species of Disa. Species that adapted to the same pollinator often independently evolved a similar floral morphology which confounded the infrageneric classification of Disa until cladistic analysis was applied to DNA sequences from this genus.<ref name=waterman2009>Template:Cite journal</ref>

Examples of convergent evolution in Disa pollination include the following:

Disa serves as an example of how speciation can be caused by changes in pollinator availability and evolution.

Some Disa species are pollinated by sunbirds and have pollinaria that stick to the feet of the sunbirds when they perch on the inflorescence.<ref>Template:Cite journal</ref>

PhylogenyEdit

The first molecular phylogeny of the genus involved comparison of nuclear ribosomal ITS1, 5.8S rDNA, and ITS2 sequences, and showed that Herschelia and Monadenia were nested within a paraphyletic Disa.<ref>Template:Cite journal</ref>

In Genera Orchidacearum volume 2, Disa and Schizodium compose the subtribe Disinae of the tribe Diseae.<ref name=go>Alec M. Pridgeon, Phillip J. Cribb, Mark W. Chase, and Finn N. Rasmussen. 1999-2014. Genera Orchidacearum Oxford University Press. Template:ISBN (volume 1), Template:ISBN (volume 2), Template:ISBN (volume 3), Template:ISBN (volume 4), Template:ISBN (volume 5), Template:ISBN (volume 6).</ref> After that volume was published in 2001, molecular phylogenetic studies showed that Schizodium is nested within Disa.<ref name=bytebier2007>Template:Cite journal</ref><ref name=bytebier2008>Template:Cite journal.</ref> Schizodium comprises only six species, all endemic to South Africa.<ref name=linder1981>Template:Cite journal</ref>

In a classification of orchids that was published in 2015, Chase et alii placed Schizodium in synonymy under Disa. They also defined the subtribe Disinae as consisting of Pachites, Disa and Huttonaea. This version of Disinae is probably not monophyletic, but was created as a holding classification, to avoid the unnecessary designation of subtribes before further studies can clarify the relationships of these three genera.<ref name=chase2015/>

SeedsEdit

The genus can be split into two groups based on the size of the seeds. Those with relatively large balloon-shaped seeds up to 1.5 mm long belong to the Disa uniflora group. The remaining species have seeds that are smaller than 0.7 mm. The Disa uniflora group comprises plants that grow along stream sides: Disa uniflora, Disa tripetaloides, Disa cardinalis, Disa caulescens and Disa aurata. They belong to the few species in Orchidaceae that do not rely on mycorrhizal fungi for germination, and are thought to be an adaptation to hydrochory.<ref>Template:Cite book</ref><ref>Template:Cite journal</ref> This pattern was later extended to split the genus into summer rainfall species and non-summer rainfall species. Those in the second group added Disa cornuta to the list of Disa seeds that germinate readily.<ref>Template:Cite journal</ref>

HorticultureEdit

The species Disa uniflora is well known as an ornamental. It is a spectacular red orchid known as "The Pride of Table Mountain."<ref>PlantZAfrica.com, Disa uniflora Bergius</ref> Other commonly cultivated species include Disa aurata, Disa cardinalis, Disa crassicornis, Disa racemosa, Disa sagittalis, and Disa tripetaloides.<ref name="rhs">Anthony Huxley, Mark Griffiths, and Margot Levy (1992). The New Royal Horticultural Society Dictionary of Gardening. The Macmillan Press,Limited: London. The Stockton Press: New York. Template:ISBN (set).</ref> Some of the species are grown only in African gardens.<ref name="harley2013">Eric Harley, Sid Cywes, and H. Peter Linder. 2013. A Disa Companion: The Art and Science of Disa Cultivation. Author House. 123 pages. Template:ISBN.</ref>

Once very rare in cultivation, Disa uniflora is gaining in popularity as a cut flower. However, they are difficult to grow, because of the needed mineral composition of the potting soil. Also, if exposed to excessive moisture, they can be easily killed by rot.

HybridsEdit

File:RedDisa.jpg
Disa uniflora flowers.

The following species have been used to create more than 400 hybrids : Disa cardinalis, Disa caulescens, Disa racemosa, Disa tripetaloides, Disa uniflora, Disa aurata and Disa venosa.

  • Disa × brendae (D. caulescens × D. uniflora) (South Africa, SW. Cape Prov.)
  • Disa × maculomarronina (D. hircicornis × D. versicolor) (S. Africa)..
  • Disa × nuwebergensis (D. caulescens × D. tripetaloides) (South Africa, Cape Prov.).
  • Disa × paludicola (D. chrysostachya × D. rhodantha) (South Africa, KwaZulu-Natal).Template:Multiple image

SpeciesEdit

File:Disa atricapilla 338555196.jpg
Disa atricapilla
File:Disa atrorubens 435082705.jpg
Disa atrorubens
File:Disa aurata 2084.jpg
Disa aurata
File:Disa baurii 436641926.jpg
Disa baurii
File:Disa bivalvata 340179494.jpg
Disa bivalvata
File:Disa caffra 109483465 (cropped).jpg
Disa caffra
File:Disa chrysostachya 2016 01 02 4349.jpg
Disa chrysostachya
File:Disa comosa (2).jpg
Disa comosa
File:Disa ferruginea 354748896.jpg
Disa ferruginea
File:Disa Graminifolia.jpg
Disa graminifolia
File:Disa longicornu02.jpg
Disa longicornu
File:Disa polygonoides 251920844 (cropped).jpg
Disa polygonoides
File:Disa purpuracens.jpeg
Disa purpurascens

Species currently (May 2014) recognized:<ref name="tammy"/>

ReferencesEdit

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External linksEdit

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