Thứ Sáu, 19 tháng 4, 2013

Disa (orchid)

The orchid genus Disa consists of 169 terrestrial orchid species in tropical and South Africa, Madagascar and along the Western Indian Ocean. Its members are primarily from South Africa, and it is most noted for the species Disa uniflora, a spectacular red orchid also known as "The Pride of Table Mountain." However, Disa bracteata also occurs near Perth, Australia.
They were named after Disa, the heroine of a Swedish legend, by the botanist Carl Peter Thunberg.
The plants grow from a fleshy tuberous root which is mostly used for the artificial sweetener maltodextrins and may attain a height of 90 cm. The flowers grow in racemes or solitary. The petals and the lip are small. The lip is nonresupinate, so the flower appears upside down compared to most orchids. The flowers consist essentially of the sepals. The flowers are colored in the whole range of red.
The orchids have usually a single species as pollinator. The evolution in Disa has gone a different way. Disa has used nearly all major pollinating insects. Furthermore, unrelated clades have evolved more than once into rather similar pollination systems :
  • flowers pollinated by butterflies have evolved twice, for example the pollination of Disa uniflora by the Table mountain Pride Butterfly Aeropetes tulbaghia (Satyrinae)[1]
  • flowers with conspicuous deception, pollinated by carpenter bees, have evolved twice.
  • long-spurred flowers, pollinated by long-tongued flies, have evolved four times.
  • night-scented flowers, pollinated by moths, have evolved three times.
This shows that a few pollinators in a region can force plant into diversification through repeated forward floral shifts.
Some Disa species are pollinated by sunbirds and have pollinaria that stick to the feet of the sunbirds when the perch on the inflorescence.[2]
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 mineralogical composition of the potting soil. Also, as most species grow in very wet environments, they can be easily killed by rot in cultivation.


Disa purpurascens Bolus


The following species have been used to create more than 80 hybrids : Disa cardinalis, Disa caulescens, Disa racemosa, Disa tripetaloides, Disa uniflora 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).

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