plants?

In a way, the answer is "any." A tank full of plants will make livebearers happy. What are your conditions? That will dictate what you can grow.
Horwort is popular, because it is bushy and tends to be easy to grow. Needs sufficient light, though.
 
I like water sprite. It can grow rooted or floating, is easy to care for, and will grow insanely fast with some nitrates, good light and some CO2. The mass of fluffy roots it puts out are good cover too.

Graeme
 
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