If you mean collectable plants specifically, there is Alkane Dust from Titan, Baryon Bough from Dreaming City, Etheric Spiral from Tangled Shore, Fossilized Hermaion Blossom from past Mercury, Glacial Starwort from Europa, Spirit Bloom from Venus, and Wormspore from the Dreadnaught. Most of these don't have a defined purpose and there is little information given about them. I don't know that there are any details on larger flora from existing destination, such as the trees on Nessus, or the flowers from the Black Garden, either