Can I just add... Since the title of this thread caught my eye, I thought I might as well throw in a useful piece of information...
In nature(and in aquariums), plants have no mobility what-so-ever, and cannot rely on their strength/weight/size for protection. Therefore, flora have come up with an ingenious invention over the past million years or so, that have enabled them to defend themselves against herbivores and other flora trying to encroach upon their territory.
This defense mechanism, is called Allelopathy. Allelopathy is the process within which a plant releases toxins that are lethal to its native enemies(e.g. herbivorious fish/mammals etc.) The toxins released are different in every plant that produces them, and the amounts released alter, varying how much is needed to deter the "enemy".
For example: Myriophyllum spicatum
produces a toxin that is fatal to blue-green algae, Duckweed
, najas marina
, and even mosquiote larvae.
Little is known about Allelopathy, it started off as a mere hypothesis, and has gradually become a fact. If anyone wishes to study more on Allelopathy, I reccomend buying the book: The Ecology of planted aquariums, by Diana Wilstad(I think thats her name)...
Sorry I got carried abit off topic there, hehe.....