Just harvest cattails with any herbivore that does high enough damage per hit to withstand the swamp, you can use theris, direbears, megatheriums, stegos, or even a trike and you will get hundreds in minutes but be careful of rhynios.

It's also worth it to bring a bronto since you can harvest rare flowers and rare mushrooms at the same time and also at a way faster rate since your attack aoe will hit trees anyway so you can just stand still them spam attack until you get nothing after your last attack.

If you are on ark use the spyglass also works since the bronto's attacks have a long damage window so after you attack you can quickly pull out your spyglass and- Wait what? I suddenly forgot what I was talking about.