Disa (plant) explained

Disa is a genus of flowering plants in the family Orchidaceae. It comprises about 182 species.[1] [2] Most of the species are indigenous to tropical and southern Africa, with a few more in the Arabian Peninsula, Madagascar, and Réunion.[3] Disa bracteata is naturalised in Western Australia, where the local name is "African weed-orchid."[4]

The genus Disa was named by P.J. Bergius in 1767.[5] [6] It was named after Disa, the heroine of a Swedish legend.[7]

Description

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.

Pollination

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.[8]

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.[10]

Phylogeny

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.[11]

In Genera Orchidacearum volume 2, Disa and Schizodium compose the subtribe Disinae of the tribe Diseae.[12] After that volume was published in 2001, molecular phylogenetic studies showed that Schizodium is nested within Disa.[13] [14] Schizodium comprises only six species, all endemic to South Africa.[15]

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.[1]

Seeds

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.[16] [17] 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.[18]

Horticulture

The species Disa uniflora is well known as an ornamental. It is a spectacular red orchid known as "The Pride of Table Mountain."[19] Other commonly cultivated species include Disa aurata, Disa cardinalis, Disa crassicornis, Disa racemosa, Disa sagittalis, and Disa tripetaloides.[20] Some of the species are grown only in African gardens.[21]

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.

Hybrids

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.

Species

Species currently (May 2014) recognized:[2]

External links

Notes and References

  1. Mark W. Chase . Kenneth M. Cameron . John V. Freudenstein . Alec M. Pridgeon . Gerardo A. Salazar . Cássio van den Berg . André Schuiteman . 2015 . An updated classification of Orchidaceae . Botanical Journal of the Linnean Society . 177 . 2 . 151–174 . 10.1111/boj.12234. free .
  2. http://apps.kew.org/wcsp/namedetail.do?name_id=62691 Kew World Checklist of Selected Plant Families
  3. Hans Peter Linder and Hubert Kurzweil. 1999. Orchids of Southern Africa. 504 pages. A. A. Balkema. .
  4. http://www.weeds.org.au/cgi-bin/weedident.cgi?tpl=plant.tpl&state=&s=&region=all&card=H67 Weeds Australia, Weed Identification, African weed-orchid, Disa bracteata
  5. Web site: Disa Query Results . International Plant Names Index.
  6. Peter Jonas Bergius. 1767. Descriptiones Plantarum ex Capite Bonae Spei: 348. (See External links below).
  7. Umberto Quattrocchi. 2000. CRC World Dictionary of Plant Names volume II. CRC Press: Boca Raton; New York; Washington,DC;, USA. London, UK. (vol. II). (see External links below).
  8. Waterman, Richard J. . Pauw, Anton . Barraclough, Timothy G. . Savolainen, Vincent . 2009 . Pollinators underestimated: A molecular phylogeny reveals widespread floral convergence in oil-secreting orchids (sub-tribe Coryciinae) of the Cape of South Africa . Molecular Phylogenetics and Evolution . 51 . 1. 100–110 . 10.1016/j.ympev.2008.05.020 . 18586527 .
  9. Johnson, S.D. . Linder, H.P. . Steiner, K.E. . 1998 . Phylogeny and radiation of pollination systems in Disa (Orchidaceae) . American Journal of Botany . 85 . 3 . 402–411 . 10.2307/2446333. 2446333 . free .
  10. Transfer of pollinaria on birds' feet: a new pollination system in orchids. Plant Systematics and Evolution . 2004. 244. 3. 181–188. 10.1007/s00606-003-0106-y. Johnson, S. D. . Brown, M.. 23288375 .
  11. Douzery. Emmanuel J. P.. Pridgeon. Alec M.. Kores. Paul. Linder. H. P.. Kurzweil. Hubert. Chase. Mark W.. 1999-06-01. Molecular phylogenetics of Diseae (Orchidaceae): a contribution from nuclear ribosomal ITS sequences. American Journal of Botany. en. 86. 6. 887–899. 0002-9122. 10371730. 10.2307/2656709. 2656709 .
  12. Alec M. Pridgeon, Phillip J. Cribb, Mark W. Chase, and Finn N. Rasmussen. 1999-2014. Genera Orchidacearum Oxford University Press. (volume 1), (volume 2), (volume 3), (volume 4), (volume 5), (volume 6).
  13. Bytebier, Benny . Bellstedt, Dirk U. . Linder, Hans Peter . 2007 . A molecular phylogeny for the large African orchid genus Disa . Molecular Phylogenetics and Evolution . 43 . 1. 75–90 . 10.1016/j.ympev.2006.08.014 . 17081772 .
  14. Benny Bytebier . Dirk U. Bellstedt . Hans Peter Linder . 2008 . A New Phylogeny-Based Sectional Classification for the Large African Orchid Genus Disa . Taxon . 57 . 4 . 1233–1251 . 10.1002/tax.574015 . 27756776. .
  15. Linder Hans Peter . 1981 . Taxonomic studies on the Disinae: 2. A revision of the genus Schizodium Lindl . Journal of South African Botany . 47 . 339–371 .
  16. Book: Thompson . David Ian . Conservation of select South African Disa Berg. Species (Orchidaceae) through in vitro seed germination . 2003 . University of Natal.
  17. Kurzweil . H. . Seed morphology in Southern African Orchidoideae (Orchidaceae) . Plant Systematics and Evolution . September 1993 . 185 . 3–4 . 229–247 . 10.1007/BF00937660. 41321812 .
  18. Thompson . Dave I. . Edwards . Trevor J. . Staden . Johannes van . In Vitro Germination of Several South African Summer Rainfall Disa (Orchidaceae) Species: Is Seed Testa Structure a Function of Habitat and a Determinant of Germinability? . Systematics and Geography of Plants . 2001 . 71 . 2 . 597–606 . 10.2307/3668704. 3668704 .
  19. http://www.plantzafrica.com/plantcd/disauniflora.htm PlantZAfrica.com, Disa uniflora Bergius
  20. [Anthony Huxley]
  21. Eric Harley, Sid Cywes, and H. Peter Linder. 2013. A Disa Companion: The Art and Science of Disa Cultivation. Author House. 123 pages. .

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