A leaf is a fundamental unit in botany and understanding what constitutes a leaf is fundamental to many plant science activities. My observations and subsequent testing indicated that many students could not confidently and consistently recognise a leaf from a leaflet, or recognise basic leaf arrangements and the various types of compound or divided leaves. Consequently I designed an online leaf morphology tutorial. Its main features are the extensive use of scans of living specimens and multiple examples for each morphology character. The tutorial is reinforced with two tests based on species not used in the tutorial. The main feature of these "ToolBook"-based tests is that after answering a question students are provided with additional text-based feedback and additional labelling on the images. Evaluation has indicated the application is at least equally effective as a hands-on session provided by a teacher or demonstrator. This indicates that the web site is particularly useful as a pre-class exercise or for distance education students. (Contains 5 figures.)