The plant specimens in a herbarium may be dead, but the collection is a living resource for botanical research. Herbaria document plant species’ distributions through time and geographic space. They are valuable reference collections for the identification of plants and are also used for studies of plant taxonomy, plant evolution and plant ecology. Increasingly, researchers are using herbaria to study our changing environment: This exhibit features an example of how their collections can provide documentation of a lost habitat.
The method of pressing and drying plants for preservation dates to the 16th century, when Luca Ghini from the University of Bologna pioneered the technique. Ghini was interested in preserving plants as a reference for medical students needing to identify plants for their medicinal value. Even today, botanists continue to use this simple technique. Plants are collected with flowers and/or fruits and then arranged between sheets of newspaper. The newspaper and specimens are sandwiched between blotters that absorb moisture and corrugated cardboard to allow airflow. The entire stack is then squeezed between wooden frames that are tightened with straps or rope. Once dry, the specimens are mounted on to sheets of archival cardstock. Crucially, a scientific collection must include a label with the species name, as well as information on collection date and locality. In this way, herbarium specimens provide definitive documentation of a given plant species growing in a given place at a given time.
Asclepias purpurascens L.
purple milkweed, Apocynaceae (dogbane family)
This plant can be found scattered across southern New England and eastern parts of the United States. It is normally rare where it occurs, and in Rhode Island the plant has not been seen in the wild since the early 1900s. Given its preference for open forests and fields, we know it grew in, or more likely near, Cat Swamp because we have a specimen collected by William Whitman Bailey in 1878, and Edward Lewis Peckham painted the plant.
The milkweed genus, Asclepias, is named for Aesculapius, the mythological god of medicine. The species name, purpurascens, refers to the purple color of the flowers.
