Hi A.,
I really prefer the 'stand up/put down' method of dealing with pinching/biting/hitting little ones of this age. When my son was little, if this happened while I was holding him, I would put him down and tell him with a firm voice: "That hurts Mama. All done now." Then I would stand up and walk over to something else, and not pick him up for about a minute. Or if he had to be on my lap, I'd turn him to face outward and give him something else to pinch or bite.
Please understand that this is a developmental phase. Kids bite when their teeth are moving, and it's not necessarily obvious to us. They may not manifest drool or other teething symptoms, but the teeth are moving around a lot under the surface, which does cause them some amount of discomfort. Biting is one way children relieve this. And the pinching is the same-- babies are practicing their pincer grip, we just need to give them other toys or cheerios to practice with, instead of ourselves.
Big reactions are also interesting, which is why he finds it 'funny'. Not that he's doing this to upset you or hurt you per se (babies can't plan to hurt other people in this way) but your big reaction is perceived by him as "wow-- I do *this* and Mama makes a big noise! Interesting!" This is why I like the "stand up/put down" discipline, because nothing is more instructive than our choosing not to give our little one attention. Letting them cry on this for one minute is not a big deal, by the way.
Some people will debate this, too, but I have found that instead of saying "no" (which is an abstract word to little ones), I try to tell the child what I would like him to do. Distraction and redirection techniques really help here. Instead of telling him "no no" about the plant, you could also help him by saying "We leave the plant alone. Let's go find a toy", walk him away by the hand and hand him an appropriate item. Or, adjust the enviroment and put the plant up. (Kids have a very difficult time staying out of plants, and some may be toxic. It may be better just to put them up.)
Hope some of these ideas help!
H.