One thing that is absolutely essential to plant growth is adequate light. Some aquatic plant species have adapted to grow in shady settings. Among them are many ferns and mosses as well as Anubias species and many Cryptocoryne species. These plants have been the long- term mainstays of the aquarium world because they grow well even under fairly dim aquariums lighting.
Other species grow wild in open areas with shallow, clear water. These plants, in general, are much more demanding in the aquarium, needing much higher light levels to thrive. Many of the most beautiful and brightly colored aquarium plants are in this category and are well worth the extra effort required to maintain them.
Cryptocoryne Cordata is an example of a plant that has adapted to grow where many other plants cannot. This particular variety, from southern Thailand, can take advantage of areas that are not only shady, but also have relatively deep hard water.
Source: Sunken Gardens/ By: Karen A. Randall