The specimens are generally filed according to a systematic classification system that not only permits ready retrieval but also serves to group specimens of closely related plants in close physical proximity. When dried properly, many plants retain their characteristic morphological features, even to the microscopic level. Herbarium specimens, therefore, are essential for teaching and research in plant anatomy, plant morphology, and plant systematics. The specimens themselves embody the morphology of the species they represent and the whole collection becomes a working example of the classification. Moreover, herbarium specimens are always accompanied by detailed labels, so the collection also provides a record of what plant grew at what place at what particular time in the past.
Specimens accumulate in herbaria for a variety of reasons.
General collections of plants are often made for the purpose of enriching the herbarium, i.e., to produce a collection that mirrors the full diversity of plant life in nature. General collecting to build an herbarium collection is much like librarians seeking all sorts of different kinds of books to place on their shelves. Some herbarium specimens, called vouchers, play an additional specialized purpose. Let's say someone wanted to study leaf development in Chamaesyce maculata. The genus Chamaesyce is large and contains many species that are sometimes difficult to distinguish from each other.