Clover And Other Exported Species

On an extrasolar planet thousands of years in the future:

"...plants with green trilobate leaves, scattered low among the reddish native pseudo-grasses... Clover was another of those life forms that man had brought with him from Old Earth, to more planets than anyone now remembered, before the Long Night fell. Often they were virtually unrecognizable; over thousands of years, evolution had fitted them to alien conditions, or mutation and genetic drift had acted on small initial populations in a nearly random fashion. No one on Kraken had known that pines and gulls and rhizobacteria were altered immigrants, until Donli's crew arrived and identified them."
-Poul Anderson, "The Sharing of Flesh" IN Anderson, Flandry's Legacy (Riverdale, NY, 2012), pp. 661-708 AT pp. 665-666.

This was why I mentioned clover as accompanying human beings to many planets here. Donli is a one-off character. Our series characters are long dead but four post-Imperial installments are scattered across several centuries and millennia in the further future.

Elsewhere, on the planet Nike:

a dense mossy carpet;
native fronded gymnosperm plants, green with presumed chlorophyll but also pale and bluish;
imported oaks, birches, cedars, primroses and grass which overcomes pseudo-moss except in the shade.

Anderson describes conflicts not only between Terrans and Merseians but also between grass and pseudo-moss. (And that reminds me that the Merseian Roidhunate has imported tea.)