The herbarium is a collection of dried plant specimens. Normally, the specimen includes reproductive parts such as flowers or fruits, which are often necessary for positive identification. Data (information) describing the collection site (i.e., country, state, county and specific location) and habitat, the date of collection, the name and serial collection number of collector, as well as other pertinent facts such as plant habit or flower color are recorded in a field notebook at the time of collection. This information is later transcribed onto a permanent specimen label that is mounted on the herbarium sheet with the specimen.
In the case of small herbaceous plants, the entire plant may be preserved. For obvious reasons, only representative portions of larger plants such as trees and shrubs are used. In order to prepare an herbarium specimen, the fresh plant specimen is placed in folded newspaper, flattened in a plant press, and then dried with warm air. Once dried, specimens are identified, sorted, labeled, mounted onto stiff sheets of high-quality paper, re-sorted systematically, and filed for storage in steel herbarium cases. Herbarium specimens will last indefinitely if properly prepared and cared for; the major hazards to be avoided are insects and water. Insect pests are controlled by freezing specimens and placing insect repellant in herbarium cases. In order to prevent infestations of damaging insect and fungal pests, climate in the herbarium should be hostile to such organisms. Thus, temperature should be maintained below 21 degrees C and the relative humidity between 30--40 percent.