Citizen science can serve as a tool to address environmental and conservation issues. Ιn the framework of Erasmus+ project CS4ESD, this study focuses on promoting the importance of plants and plant species and communities’ diversity by using available web-based information because of Covid-19 limitations and concerning the case study of Olympus mountain Biosphere Reserve (Greece). A questionnaire was designed to collect the necessary information, aiming to investigate pupils’ and students’ willing to distinguish and learn more about plant species and communities and evaluate information found on the web. Pupils, students, and experts participated in this study. The results are indicative of young citizens’ ability to evaluate environmental issues. They often underestimate plant species richness, endemism, plant communities, the importance of plants, and ecosystem services. They also use environmental or plant-based websites and online available data in a significantly different way than experts. The age of the young citizens is a factor that may affect the quality of data. The essential issue of recognizing the importance of plants and plant communities and of assisting for their conservation is highlighted. Education for sustainable development is one of the most important tools that facilitates environmental knowledge and enhances awareness.