If i remember correctly waltorius said that one flower is a bit hard and you get some trophy.
Yes, starting in Chapter 2 there is a unique, extra-tough archespore that you can kill for a trophy. It's actually the very first archespore I encountered in the game. That one shows up during the day, though, in a few different locations.
I generally noticed that in daytime I only really ever encountered archespores, but at night there were a few echinops too. I didn't spend too much time in the swamps at night though since there's so many monsters.