Eurasian water-milfoil is the most well known example of such a plant. It was introduced to North American lakes about twenty years ago and because it can grow from small fragments, it has spread very quickly, choking many lakes. In British Columbia, this plant has invaded lakes in the Okanagan valley and is threatening lakes on Vancouver Island. We must be able to identify it before we can eradicate it from a lake. Even plants from unrelated groups can be hard to distinguish.
Botanists use many different techniques to tell similar species apart.
Sometimes they have to look for microscopic features and sometimes they have to examine plant chemistry to identify a plant. The classification of aquatic plants is a challenging and fascinating part of botanical research. It provides the basis for understanding the life in and around lakes, and a key to managing the resources connected with freshwater ecosystems. The Royal British Columbia Museum, 1985. Clark, L.J. Lewis Clark's Field Guide to Wild Flowers of Marsh and Waterway in the Pacific Northwest.