Could alien planets have purple plants?

Yes — alien planets could plausibly have purple plants or other purple photosynthetic life.

Scientists think this is possible because life elsewhere would adapt to its star’s light, and different pigments could make organisms appear purple. On Earth, some microbes use retinal-based light-harvesting, which can produce purple coloration, so purple-colored energy-harvesting biology is scientifically plausible even though Earth did not necessarily have purple plants.

It’s also reasonable to expect that planets around different types of stars — especially red dwarfs — might favor pigments tuned to red and infrared light, which could lead to colors like purple, red, black, or something else entirely.

So the short answer is: yes, purple alien plants are possible. We just don’t know yet because we haven’t found extraterrestrial life.