Students may acquire mislearnings in the course of their academic lives for various reasons and keep them for a lifetime. Some of the most common of those mislearnings are the alternative conceptions university students have about Biology lesson. This study was conducted through one-to-one interviews with 54 students at the 1st grade of the Department of Classroom Teaching in order to determine university students' alternative learnings about the classification and the diversity of plants and remove these alternative learnings if there were any. In the end, it was found that students had mislearnings about the classification and the diversity of plants. The main mislearning was that students classify some of the plants they knew well in a wrong way according to the criteria which was not biological; for example, they thought fern and bryophyte were plants with seeds, fungi were plants, and the plants belonging to the family of Pinaceae did not have real leaves so they were included in the class of plants without seeds. In order to remove these mislearnings 'Porphyrios Tree', which has a structure similar to a concept map, was used. As a result, a great majority of pre-service teachers' alternative conceptions about the classification of plants were removed through this method of application.