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This EarthWord is your best friend in Scrabble or Words With Friends...

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

Image shows orange and yellow flowers.
Image shows orange and yellow flowers. Credit: Elizabeth Sellers, USGS.

The EarthWord: Zygomorphic


  • No, not a Xenomorph, like on the movie Alien. Zygomorphic is about as far away as you can get, actually—it refers to flower symmetry. There are two main types of flower symmetry, zygomorphic and actinomorphic.

  • Zygomorphic flowers have bilateral symmetry, meaning the petals can only be divided one way to form mirror images of each other. Zygomorphic symmetry can also be referred to as irregular symmetry, and is most common in flowers that have at least two differently sized petals. Classic examples include orchids.


  • Zygomorphic is made up of the Greek prefix zygo-, meaning “a pair,” and the Greek morphe, which means “shape.”

Use/Significance in the Earth Science Community:

  • Whether a flower is zygomorphic or actinomorphic in symmetry is useful in taxonomy, the study of species. As climate change and invasive species affect biodiversity, taxonomy is a vital tool for determining whether or not a species is endangered and in need of protection.


  • USGS studies biodiversity of plants, animals, and other organisms as part of its Ecosystems Mission Area, as well as the effects of climate change on biodiversity in its Climate and Land Use Change Mission Area.

Next EarthWord: We’ve finished the alphabet! Next up is a world-tour of scientific terms from foreign languages!

Hungry for some science, but you don’t have time for a full-course research plate? Then check out USGS Science Snippets, our snack-sized science series that focuses on the fun, weird, and fascinating stories of USGS science.

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