Modern phylogenetics Zimmermann’s contributions to systematics have largely been overlooked, though
Willi Hennig’s pivotal publication in 1966 on phylogenetic systematics cites Zimmermann multiple times. In fact, Hennig personally considered Zimmermann as “one of the most zealous of modern advocates of a consistent phylogenetic systematics.” Zimmermann’s principle paper contributing to modern systematics published in 1931 did not become widely available until 1937 and was located adjacent to articles of unrelated topics, possibly contributing to Zimmermann’s lack of recognition. His primary goal in
classification was to separate the subject from the object, or attempting to characterize groups objectively rather than based on philosophical
idealism and
metaphysical properties. Though he recognized the importance of subjective human abstractions in categorizing organisms, he strayed as far from that view as possible when identifying key phylogenetic characters based on
phenetic differences. Zimmermann pinpointed three main phylogenetic methods of grouping organisms used during his time: special purpose, idealistic, and phylogenetic. The special purpose method involves the random choosing of basic forms or types for a practical purpose, which Zimmermann acknowledged as artificial. He considered biased the idealistic method, which focuses on a form chosen intuitively based on human idealism and does not need to actually exist in nature. Zimmermann campaigned for the phylogenetic method, an objective way of grouping organisms based on
genealogy. He preferred the phylogenetic method because common ancestors once existed in reality and are not human constructs as in the case of these other two grouping methods. Though he acknowledged that these three methods can coexist, they should not be used together in the same system or same analysis. In other words, he proposed that organisms should be grouped based on whether they shared a recent phylogenetic splitting event or
common ancestor. His methodology included three main steps: (1) identifying whether evolution has occurred in the given group, (2) determining the trajectory of evolution, and (3) revealing the causes of this evolutionary trajectory.
Plant systematics One of Zimmermann’s major goals was to improve the plant systematics and
taxonomy using informative phylogenetic morphological and developmental characters, such as plant
telomes. Specifically, Zimmermann founded the
telome theory, stating that telomes, or the most terminal ends of dichotomizing plant
branching systems, evolved to form more complex structures such as leaves, roots, and reproductive organs of
ferns and other
vascular plants. He utilized this theory in plant classification to reveal insights about how aquatic plants first colonized land and the evolution of basal vascular plants. Tracing character state changes of single traits helped elucidate the evolutionary relationships between organisms, such as in identifying the parallel transition of
isogamy to
anisogamy. Zimmermann contributed insight into the evolution of the
stele (central part of the root system of plants) by considering phylogenetic similarities and attempting to deduce its ancestral morphology. He tracked across plant phylogenies the common shifting of different plant tissues and organs, such as increases in the
meristele number,
pinnation of fern leaves, and the occurrence of plant
neoteny. In addition, he aided in the classification and taxonomy of many plant groups, such as
embryophytes. == List of selected publications ==