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Convergent evolution  [ Biology ]

Dictionary of botanic terminology - index of names

Synonyms: Evolutionary convergence,  Homoplasy
     
  The convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving by adaptation in separate ecosystems.  
     


Euphorbia obesa
(family Euphorbiaceae)

Astrophytum asterias (family Cactaceae)

The evolutionary convergence is the recurrent tendency of living beings to arrive at the same 'solution' to a particular 'biological problem” that can often only be handled in one of a few ways, some particular patterns emerge over and over again in very different organism.

Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures which have a common origin.

An example of convergent evolution is the similar external appearance of the ribbed stems of some cacti, euphorbias, Stapeliads and of other succulents belonging to different family. All them serve the same function and are similar in structure, but each evolved independently.

An other example:
The Mexican Astrophytum asterias (family Cactaceae) resembles enough to the South African Euphorbia obesa  (family Euphorbiaceae), but only in the field of the external anatomy, this being due to the environmental condition in which these two types of plants live.

Parallel evolution occurs when two independent species evolve together at the same time in the same ecosystem and acquire similar characteristics
     

 

 


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Holdfast roots  [ Botany  ]

Dictionary of botanic terminology - index of names

 
     
  Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.  
     
Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans),  develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994
   

 

 

 

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