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Speciation in plants

In terms of reproduction, plants have a lot more options than animals do. Many plants can reproduce sexually, by fertilizing other individuals or themselves, and asexually, by creating clones of themselves through vegetative reproduction, while most animals only reproduce sexually.

Similarly, in terms of speciation, plants have more options than animals do. Two modes of speciation are particularly common in plants:

  • Speciation by hybridization: For example, when Loren Rieseberg and coworkers reconstructed the phylogeny of several sunflower species, they found that several species had been formed by fertilizations between other species. Often the hybrid offspring of such fertilizations are sterile, but occasionally they are fertile and are reproductively isolated from their "parent" species. In the latter case, a new species is formed.

    Helianthus annuus Helianthus petiolarus Helianthus anomalus
    The sunflower species Helianthus anomalus was produced by the hybridization of two other sunflower species.

  • Speciation by ploidy changes: In terms of plant speciation, a ploidy change generally means multiplying the number of chromosomes the species has by some number. So a species that normally has 18 chromosomes might produce a lineage that has 36 or 54 chromosomes. Ploidy changes are common in plants and often produce a species that is reproductively isolated and distinct from the "parent" species. For example, speciation in these anemones involved a ploidy change.

    anemone flowers and their chromosomes
    Here we see two species of anemone flower and their chromosomes. Changes in number of chromosomes, as has occurred in this genus, can cause speciation.

Sunflower photos courtesy of Jason Rick and Loren Rieseberg; Anemone rivularis photo courtesy of Farmyard Nurseries; Anemone quinquefolia courtesy of Thomas G. Barnes @ USDA-NRCS PLANTS Database / Barnes, T.G. & S.W. Francis. 2004. Wildflowers and ferns of Kentucky. University Press of Kentucky.

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