Could alien planets have black plants?

Yes—alien plants could plausibly be black, though it’s speculative. On Earth, plants look green mainly because chlorophyll absorbs red and blue light and reflects more green. On another planet, the color of photosynthetic life would depend on the star’s light and the local environment.

Around a dim red dwarf, for example, life might evolve pigments that absorb a very broad range of available wavelengths, which could make the organisms appear very dark or even black to our eyes. That said, there’s no single guaranteed outcome: alien photosynthesizers could also end up purple, red, brown, or some other color depending on the conditions.

So black alien plants are a reasonable possibility, but we can’t know for sure without knowing the planet’s star, atmosphere, and biology.