Difference between revisions of "Orchidaceae"

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[[Image: Orchidaceae.jpg|thumb|right|300px|Orchidaceae]]
  
 
'''Description:''' A huge family of plants (> 20,000 species worldwide), all herbaceous, some climbing. The leaves are alternate and often distichous, usually with a basal sheath and a storage structure called a pseudobulb at the base. Orchid flowers are almost always zygomorphic (i.e., bilaterally symmetrical), and many display bizarre and unique adaptations to attract pollinators (Endress 1994). Some species mimic other nectar-bearing flowers, without bearing nectar themselves. The pollinators are tricked into carrying their pollen without a reward. Some species mimic female bees or wasps. The male pollinates the flower as he attempts to copulate with it. Other species have elaborate mechanisms that trap the pollinator and send it tumbling down a slide, where the pollen is fixed onto the pollinator’s body. Orchid pollen is carried in packets called pollinia, ensuring that all the ovules of one flower are pollinated by a single parent. Mutations can spread very rapidly in this sexual system, and this may have contributed to the rapid speciation in the family (Judd et al. 2002). The seeds of orchids are tiny, almost microscopic, and wind-dispersed. Orchids depend on mycorrhizal fungi as symbionts, and will not even germinate without fungi present (Bell 1991). Gentry (1993) includes an excellent key to the genera of Orchidaceae.
 
'''Description:''' A huge family of plants (> 20,000 species worldwide), all herbaceous, some climbing. The leaves are alternate and often distichous, usually with a basal sheath and a storage structure called a pseudobulb at the base. Orchid flowers are almost always zygomorphic (i.e., bilaterally symmetrical), and many display bizarre and unique adaptations to attract pollinators (Endress 1994). Some species mimic other nectar-bearing flowers, without bearing nectar themselves. The pollinators are tricked into carrying their pollen without a reward. Some species mimic female bees or wasps. The male pollinates the flower as he attempts to copulate with it. Other species have elaborate mechanisms that trap the pollinator and send it tumbling down a slide, where the pollen is fixed onto the pollinator’s body. Orchid pollen is carried in packets called pollinia, ensuring that all the ovules of one flower are pollinated by a single parent. Mutations can spread very rapidly in this sexual system, and this may have contributed to the rapid speciation in the family (Judd et al. 2002). The seeds of orchids are tiny, almost microscopic, and wind-dispersed. Orchids depend on mycorrhizal fungi as symbionts, and will not even germinate without fungi present (Bell 1991). Gentry (1993) includes an excellent key to the genera of Orchidaceae.

Revision as of 16:30, 9 June 2008

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Orchidaceae

Description: A huge family of plants (> 20,000 species worldwide), all herbaceous, some climbing. The leaves are alternate and often distichous, usually with a basal sheath and a storage structure called a pseudobulb at the base. Orchid flowers are almost always zygomorphic (i.e., bilaterally symmetrical), and many display bizarre and unique adaptations to attract pollinators (Endress 1994). Some species mimic other nectar-bearing flowers, without bearing nectar themselves. The pollinators are tricked into carrying their pollen without a reward. Some species mimic female bees or wasps. The male pollinates the flower as he attempts to copulate with it. Other species have elaborate mechanisms that trap the pollinator and send it tumbling down a slide, where the pollen is fixed onto the pollinator’s body. Orchid pollen is carried in packets called pollinia, ensuring that all the ovules of one flower are pollinated by a single parent. Mutations can spread very rapidly in this sexual system, and this may have contributed to the rapid speciation in the family (Judd et al. 2002). The seeds of orchids are tiny, almost microscopic, and wind-dispersed. Orchids depend on mycorrhizal fungi as symbionts, and will not even germinate without fungi present (Bell 1991). Gentry (1993) includes an excellent key to the genera of Orchidaceae.

Economic uses: Orchidaceae are very popular with greenhouse growers, due to their long-lasting flowers (some species bloom for 4-6 weeks). Vanilla planifolia and V. fragans are the source of natural vanilla flavoring. They are native to the Neotropics, but extensively cultivated in Asia. Where their native pollinators are absent, the orchids must be pollinated by hand. This contributes to the high price of natural vanilla.


Descripción: Una familia muy grande (> 20,000 especies en el mundo) de plantas herbáceas, a veces trepadoras. Las hojas son alternas y frecuentemente dísticas, usualmente con la base envolvente y una estructura engrosada en la base del tallo que llamado “pseudobulbo.” Las flores son zigomórficas (es decir, con simetría bilateral), y muchas tienen adaptaciones extrañas y fascinantes para atraer a los polinizadores (Endress 1994). Algunas especies aunque no producen néctar, imitan flores que si lo producen néctar, engañando a los polinizadores sin darles ninguna recompensa por sus servicios. Unas especies imitan las hembras de algunas especies de avispas o abejas. El macho poliniza la flor mientras trata de copular con ella. Otras especies tienen mecanismos complicados que atrapan a los polinizadores y pegan el polen en sus cuerpos. El polen de las orquídeas está agrupado en paquetitos llamados polinios, que aseguran que todos los ovarios de una flor reciban el polen del mismo parental. Las mutaciones pueden diseminarse muy rápidamente en las poblaciones con este tipo de sistema sexual. Esto probablemente contribuyó a la gran cantidad de especies que hay en esta familia (Judd et al. 2002). Las semillas de las orquídeas son muy pequeñas, casi microscópicas, y dispersadas por el viento. Las orquídeas necesitan hongos que forman micorrhizas, y las semillas no germinan sin que estos hongos estén presentes (Bell 1991). Gentry (1993) incluye una excelente clave diagnóstica para los generos de Orchidaceae.

Usos económicos: Las Orchidaceas son muy populares en invernaderos, porque sus flores duran por mucho tiempo (algunas por 4-6 semanas). Las semillas de Vanilla planifolia y V. fragans se usan para elaborar el sabor de vainilla. Las flores son originalmente de la zona neotropical, pero ahora se cultiva en muchas partes del sur de Asia. Allí no estan presentes los polinizadores. Por lo tanto se necesitan trabajadores para polinizar las flores manualmente. Eso contribuye a aumentar el precio del sabor natural de vainilla.


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