You seem to be predicting that grasses have smaller genomes than trees, but wheat is famous for having a huge genome.
If you want to be exact I didn't say genome size but waste. Through mutation inactived genes, retroviruses and so on. It takes time to remove them.
Do you have evidence that the variation in genome size among multicellular organisms is not variation in waste? Added: As far as I know, the consensus is that it is. If you disagree with the consensus, you should acknowledge that's what you're doing.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.