高階植物的分子演化多以演化速率慢的胞器基因或核內低套數基因進行演化分析，演化速率較快的多套數基因，則少用以分析高階植物物種間的分類。本試驗利用14個物種的expansin基因進行物種間與物種內分子演化分析，分別探討多套數基因是否能做為高階植物的演化分類工具與expansin基因家族間的分子演化過程。演化分析試驗以演化早期的青綠藻做為標準，以胺基酸序列相似度篩選出直系同源基因，並以cDNA序列與胺基酸序列繪製最大似然法、最大概度法與近鄰結合法演化樹，探討物種間的高階演化關係，後又以物種內的expansin基因家族cDNA與胺基酸序列所繪製的演化樹探討物種內分子演化。試驗結果顯示若將直系同源基因的篩選標準提高，以核內多基因套數家族探討高階植物的演化分析便具有相當的可信度。在expansin基因的分子演化中，expansin基因的演化方向決定於基因重複與內隱子插入的事件，並從ExpA與ExpB兩次家族演化至ExpA、ExpB以及ExpL三次家族。以多套數基因進行演化分析，未來不只可進行高階植物的演化分類，還可了解植物間的分子演化過程，進一步連結演化過程中，多基因家族基因分子層面的改變如何影響植物的演化。 The phylogeny was the evolution of species and taxonomic grouping in an organism by using bioinformation. The ribosome DNA, chloroplast DNA and low-copy nuclear genes were used in phylogeny analysis, because their sequence divergences were slow. A new method that using multiple copies of nuclear genes could improve the robustness of phylogenic reconstruction. The expansin gene families were used in this study. There were three sub gene families in expansin gene which was partaking in plant development. The orthologous genes which show the highest similarity with the amino acid sequences of Ostreococcus tauri was selected from thirteen plant species. Then, the phylogeny tree was drawn by using Maximum likelihood (ML), Maximum parsimony (MP), Neighbor-joining (NJ) method with cDNA sequences and amino acid sequences. The expansin gene sequences were also compared the difference with molecular level in these species. The method was a useful tool to analyze the plant evolution at higher taxonomic levels and combined with molecular phylogeny of species by using multiple nuclear genes. However, the criterion of orthologous genes was stricted. At the molecular level, expansin gene was an ancestor gene in plant, and gene duplication and intron gain event happened in the course of plant evolution.