This paper presents a generalized geometric foliage simplification method to efficiently construct multi- resolution models for leaves with complex shapes. It includes two phases: preprocessing and rendering. In the preprocessing, we perform the simplification hierarchically in three levels: single leaf, phyllotaxy group and whole crown. We first simplify each single complex leaf to a quadrilateral. Then, we implement the progressive leaf collapse in the phyllotaxy group and the crown one after the other. To accelerate the preprocessing, we search for the best leaf pair in a limited scope, where the pairs of leaves impossible to be collapsed are eliminated in advance. During the rendering, we determine detail levels for leaves locating in different positions of the crown according to the distance from the viewer to the rendered tree, and a statistical visibility. Finally, the less visible leaves are rendered coarsely. As a result, visual quality is maintained while the overall compression ratio is higher.