Flora refers to all the plant life present in a particular region or time, generally the naturally occurring native plants. The term "flora" is derived from the Latin name of Flora, the goddess of plants, flowers, and fertility in Roman mythology. Flora can be grouped based on region (floristic regions), period, special environment, or climate. Floras can mean plant life of a historic era as in fossil flora. Moreover, floras may be subdivided by special environments such as native flora, agricultural and horticultural flora (garden flora), and weed flora. A Flora is a publication of scientific descriptions of plants occurring within a given region. It may contain anything from a simple list of the plants occurring in an area to a very detailed account of those plants. Floras almost always contain scientific names, and they may also include common names, literature references, descriptions, habitats, geographical distribution, illustrations, flowering times, and notes. Sometimes the plants are listed alphabetically, and sometimes they are represented within a classification system that indicates which plants are most similar or are thought to be related. Floras often also include devices called "keys" that enable the user to identify an unknown plant.