The native plants of a given area in California are those that grew there prior to European contact. California's native plants evolved here over a very long period, and are the plants which the first Californians knew and depended on for their livelihood. Our native plants have co-evolved with animals, fungi and microbes, to form a complex network of relationships. These plants are the foundation of our native ecosystems, or natural communities.
Specimens, seeds and drawings of new world plants were taken to Europe by early explorers over many years. Thus, American plants were included in ongoing botanical studies of the world's flora. In modern times the science of paleobotany allows scientists to carry out detailed studies of plant fossils. By comparing fossil records with modern plants, researchers can confirm their theories as to which plants are native to an area. While there is general agreement among plant scientists on which California plants are native, disputes can arise. An example is the Sea Fig, or Common Coast Ice Plant, (Carpobrotus chilensis) once thought to be native, but now widely regarded as an alien. Other questions involve the original distribution of some plants, such as the northern range limit of the Coast Bush Lupine (Lupinus arboreus).
Our native plants, having evolved here, are best suited to perform the macro tasks that plants do, such as manufacturing oxygen and filtering impurities from our water. These plants also do the best job of providing food and shelter for native wild animals. Maximum diversity in animal populations requires maximum diversity of plants. Biological diversity is vital to humans, because ultimately, we all live off the land, whether we admit it or not. Native plants continue to play a crucial role in the development of new foods, medicines and industrial products. Commercial sunflower seeds were developed using our Common Sunflower (Helianthus annuus). The Pacific Yew (Taxus brevifolia) yields Taxol, an anti-cancer drug. Monterey Pine (Pinus radiata) is an important timber crop throughout much of the world. Native plants are also a major element in the natural beauty for which California is famous.
When non-native plants spread and become established in wild areas, they are referred to as "naturalized." Some of these plants, such as forget-me-nots and field mustard are wide-spread, but generally do no great harm. Others take over natural areas and out-compete or smother native plants. They can do this because the natural pests, diseases or weather conditions which kept the plants in check in their homeland are missing in California. These weeds deprive our wild animals of food and shelter, since native animals cannot make much use of them. Weeds do damage in waterways, as well as on dry land, clogging water flow and choking out aquatic plants essential to wildlife. Many weeds belong to the grass, pea and daisy families, with Medusa-head (Taeniatherum caput-medusae), Scotchbroom (Cytisus scoparius) and Yellow Star-thistle (Centaurea solstitialis) as well known examples.
