According to the U.S. Forest Service, there are 8,840 rare plants in the United States. A plant doesn't have to be endangered or even threatened to be rare; in fact there are only 764 plants listed as endangered under the Endangered Species Act. NatureServe, a conservation organization, ranks plants on a 5-point scale from critically imperiled to secure. Classifying rare flowering plants helps promote biodiversity.
Wildflowers become rare for several reasons. Human influence, natural causes or a combination of both can lead to a plant's decline. Development, gardening with invasive plants and pollution are man-made factors that can place a plant species at risk. Natural forces include the loss of pollinators to disease and insect infestations. Some plants have self-limiting requirements, such as needing soils that exist in inaccessible places. Sometimes no clear cause for rarity can be found.
Every rare plant is at some risk of extinction. According to the U.S. Forest Service, "stochastic" risk is the possibility of a random event, such as a flood, destroying an entire population. Some rare plant populations are vulnerable to certain diseases. Others are at risk from human influences, such as wildflower collecting, or from nature, such as a drought. The hardest plants to conserve or those whose numbers are declining without a clear cause.
Each state has its own list of plants that need protection. A wildflower that is listed as rare in one state may not be in another. Misconceptions occur. These are called "garden gossip" by Wildflower Information, which cites the example of the pink lady slipper (Cyprepedium). The belief that this wildflower is endangered is held in Illinois and Tennessee. Twelve states have no listing for the plant, much less a "rare" listing.
Effects of Fire
Wayne Owen of the USDA Forest Service researched the effects of fire on 186 rare plants on Forest Service lands and found that 47 of them needed fire for their populations to survive. Owen says that smooth coneflower (Echinacea laevigata), for example, requires the openness that fire provides. Two species of trillium, a variety of skullcap (Scuttellaria) and a lichen are the only types of plants to suffer adverse effects from fire.
The Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) is an agreement between 169 countries to prohibit, limit or oversee the selling of rare plants. Orchids and pitcher plants, for example, are protected under CITES. NatureServe gathers global data on rare plants and ranks them for purposes of protection. The effects of climate change on plants is also a global concern. Kew Gardens in England operates a seed bank in a partnership with 50 countries and has already banked 10 percent of the world's plant species.