An Interactive Dichotomous Key (IDK) for 390 "taxa" of vascular plants from the Ria de Aveiro, available on a website, was developed to help teach botany to school and universitary students. This multimedia tool includes several links to Descriptive and Illustrated Glossaries. Questionnaires answered by high-school and undergraduate students about the IDK showed that students considered it a "fully efficient" way to identify plants. Undergraduate assessment tests on plant identification, also improved after the use of IDK. The IDK is an effective multimedia tool in the teaching of botany, compared to conventional dichotomous keys (CDK). (Contains 2 tables and 1 figure.)