The planning, execution, and evaluation of practical classes in rocky shores of marine beaches along the Brazilian coast is a challenging teaching activity for educators when it comes to addressing botanical content. The development and approval of taxonomic photographic guides of marine flora can facilitate the pedagogical work of the instructor. The objectives of the article are: a) to present the "Guide to Green (Chlorophyta), Brown (Ochrophyta), and Red Algae (Rhodophyta) from Saco de Dois Rios, Ilha Grande, Rio de Janeiro, Brazil"; b) to describe the evaluation of its didactic adequacy made by the students of the mandatory discipline of Plant Biodiversity I of the Biological Sciences course of the State University of Rio de Janeiro. The guide is portable, submersible, and printed on a PVC plate with 29 cm in length, 20.9 cm in width, and 0.2 cm in thickness. It has 48 color illustrations: 10 Ochrophyta, 11 Chlorophyta, and 27 Rhodophyta. Students between 19-21 years old, (72%), and from the Bachelor's program (66%) approved the guide with a significant difference (a<1%) of favorable observations (76%). The tested guide proved to be an adequate complementary didactic support on the content of macroalgae for adoption in the practical classes of the rocky marine and estuarine shores studied.