Hiscock's book a decent reference book, but IMO the best plant book out there is Aquarium Plants by Christel Kasselmann. It's a bit outdated, but has the best info of any book out there. Ecology of the Planted Aquarium by Diana Walstad is my all-time favorite. She explains the science behind the aquariums and why things work like they do. I've read it cover-to-cover probably 15 times and I learn something new each time.Peter Hiscock's Encyclopedia of Aquarium Plants, is several years old but is still awesome.