In 1753, the Swedish botanist Carl Linnaeus published Species Plantarum, establishing the binomial system of naming plants. Each new plant species must be described in Latin and published in a recognized scientific journal or book. Today, rules governing plant nomenclature are established at the International Botanical Congress, which meets every six years. Nearly 5,000 botanists attended the XVI Congress in St. Louis.

At the discretion of the taxonomist, the name can honor the plant's discoverer, describe an interesting feature of the plant, or relate to the geographical region where it is found. As part of the formal description, the botanist must designate one collection from among those studies as the type for the new species. The type specimen assumes special importance - it becomes the physical reference point for the new name.

The Garden herbarium includes more the 80,000 type specimens, including many newly discovered American species named by George Engelmann and Asa Gray in the 19th century.