I'm watching a sci fi series and a character who is a biologist claims "even on Earth there are species which is debatable if they should be classified as animals or plants". I looked for examples of this and I couldnt find any. Is this true? Are there species which is debatable if they should be classified as animals or plants?


No, there are no such debates. Plants and animals diverged over a billion years ago. Animals are defined by the unique molecules that are secreted by the cells, and fill the intercellular matrix, like collagen. Plants have unique cell walls, chlorophylls a and b, and plastids. The unique characteristics of plants are given here: http://www.bio.miami.edu/dana/160/160S10_10.html Although there may be animals like sponges that don't seem to move around a lot, or corals that have symbiotic relationships with algae, simply "behaving like a plant" does not make them plants. Similarly, there are plants that move and trap insects. But taxonomists would never confuse them with animals.

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  • $\begingroup$ According to this, the Orobanche fasciculata belongs to the Plantae kingdom but it doesnt have chlorophyll en.wikipedia.org/wiki/Orobanche_fasciculata. So what we have left is cell walls and plastids for all plants, right? $\endgroup$ – Pablo Aug 16 '19 at 13:25
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    $\begingroup$ Its a plant. Snakes don't have legs, but are still considered "Tetrapods". Loss of characters, such as chlorophyll in derived lineages simply means that their ancestors had chlorophyll, and then lost it. Loss characters can confuse taxonomists, but do not change taxonomy. $\endgroup$ – Karl Kjer Aug 16 '19 at 13:38
  • $\begingroup$ "(Lost) characters can confuse taxonomists, but do not change taxonomy" - this is an excellent quote. $\endgroup$ – Bryan Krause Aug 16 '19 at 18:35
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    $\begingroup$ To add, modern taxonomy relies on genetics and not morphological/phenotypic characteristics. There are unicellular organisms like euglena that can photosynthesize but they are not plants (they are not animals either). $\endgroup$ – WYSIWYG Aug 16 '19 at 22:56

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