The science of plant morphology: definition, history, and role in modern biology.

As a scientific discipline, plant morphology is 211 yr old, originated by Goethe in 1790. It is a discipline that has largely been Germanic in practice. Because it took its origins from the study of the natural history of plants and the United States is principally an engineering society, the discipline of plant morphology in its pure form has never been widely practiced in this country. What has been labeled "plant morphology" in the United States has served largely as a handmaiden for systematics, using morphological characteristics to carve up diversity into its systematic subunits. Because the heart of plant morphology as a science is a focus on the convergences rather than the homologies in a phylogenetic sense, the German tradition of plant morphology is a unifying science that focuses on fundamental themes that transcend systematic boundaries. This paper traces the history of the science of plant morphology through the lineage of its principal practitioners: Goethe, Hofmeister, von Goebel, and Troll. It also evaluates the principles of plant morphology by applying them to the phyletically diverse Pteridophytes, showing that contemporary members of that group exhibit levels of shoot organization comparable to that of seed plants and discusses the implications of these findings.