206 



Plants — Our Livniii Rc.scunfs 



by 



Larry E. Morse 



The Nature Conservancy 



John T. Kartesz 



North CaroUna Botanical 



Garden 



Lynn S. Kiitner 



The Nature Conservancv 



No of native plants 



■ >4.000 



□ 3,000 - 3,999 



□ 2,400-2,999 



□ 2,000 - 2,399 

 n 1,600-1,999 



□ <1,600 



Fig. 1. The number of native vas- 

 cular plant species in each state. 



GH/GX G1 G2 G3 G4 G5 



Fig. 2. The number of native vas- 

 cular plant species in the United 

 States in each global rank. GH/GX 

 means species is potentially 

 extinct; Gl to G5 rank the species 

 from rarest (Gl) to most common 

 (G5). 



species is found growing outside cultivation, it 

 is considered an exotic species in that area. 

 About 5,000 exotic species are known outside 

 cultivation in the United States. While many 

 exotic plant species are desirable in some con- 

 texts (such as hoiliculture), hundreds of inva- 

 sive non-natives have become major manage- 

 ment problems when established in places val- 

 ued as natural areas (McKnight 1991; U.S. 

 Congress 1993). A few particularly troublesome 

 non-natives are regulated under specific federal 

 or state laws as noxious weeds. 



Geographic Distribution 



Western and southern states have the largest 

 numbers of native vascular plant species in the 

 country. (Fig. I, revised from Kartesz 1992). 

 California, with more than 5,000 native vascu- 

 lar plant species, has almost one-third of the 

 total number for the entire United States. Texas, 

 with about 4,500 native species, ranks second. 

 Arizona, Florida. Georgia, New Mexico, and 

 Oregon all have over 3,000 native species. 



Hawaii, as a remote oceanic island archipel- 

 ago, has relatively few native species (Carlquist 

 1970), but nearly all (89'7f) of the native 

 Hawaiian flowering (angiosperm) species are 

 endemic to that region (Wagner et al. 1990). A 

 small number of vascular plants, including a 

 species of lycopod (Hiiperzia haleakalae). are 

 native to both Hawaii and the North American 

 mainland. 



In every state, hundreds of plant species are 

 established as exotics. States with coastal areas, 

 major agricultural regions, and large cities gen- 

 erally have the highest numbers of non-native 

 plants. A modest number of native U.S. species, 

 such as the northern catalpa iCatalpa specii>sa), 

 have also spread from cultivation beyond their 

 native ranges. Some familiar mainland species, 

 like a wild blackberry {Rnbus argutiis) and a 

 grass known as broomsedge (Amlropogon vir- 

 giniciis), have become problem weeds in 

 kawaii (Smith 1989). 



Rare Species 



As of February 1994, 403 native U.S. 

 species, subspecies, or varieties of vascular 

 plants and one nonvascular plant have been for- 

 mally protected under the provisions of the U.S. 

 Endangered Species Act of 1973 (USFWS 

 1994). Nearly half the 822 native U.S. federally 

 listed species are plants. The U.S. Fish and 

 Wildlife Service considers an additional 1,953 

 kinds of plants as candidates for such listing 

 (Federal Register 1993). 



The first U.S. national lists of rare plants 

 depended largely on nominations from special- 



ists already familiar with various rare species 

 and omitted many potential candidates. Many 

 state-level rare plant lists were also developed 

 in the 1970"s: these generally addressed species 

 considered rare in a particular area regardless of 

 abundance elsewhere. 



The Nature Conservancy and the network of 

 Natural Heritage Programs use a consistent 

 methodology to inventory natural diversity and 

 to assess rarity and endangerment for all cur- 

 rently recognized species of vascular plants in 

 North America, Hawaii, and portions of Latin 

 America (Jenkins 1985). By using a five-level 

 scale from I (rarest and most vulnerable — typi- 

 cally five or fewer existing occuiTences) to 5 

 (demonstrably widespread, abundant, and 

 secure), a global or rangewide rank (Gl to G5) 

 is determined for each species. With the use of 

 the same five-level scale, conservation priority 

 ranks are assigned for national (Nl to N5) and 

 subnational or state (SI to S5) status. Ranks are 

 used conservatively throughout the Natural 

 Heritage Network and are assigned after careful 

 review of a species" status. Additional ranks are 

 used to indicate species that occuned historical- 

 ly within a jurisdiction, but which are not 

 presently known. A species is presumed extinct 

 if effoils to relocate it are unsuccessful, if no 

 suitable habitat remains, or if the loss has been 

 well documented. Species are considered "his- 

 toric" (possibly exfinct) if there is reliable evi- 

 dence from biological surveys that the species 

 occuiTcd within the past few centuries in a given 

 area (Snyder 1993). 



The Natural Heritage Network has docu- 

 mented the status of thousands of rare species. 

 At the same time, plant surveys have shown that 

 a comparable number of plants are substantially 

 more common than previously believed. 

 Species status infoiTiiation from all 50 U.S. 

 State Natural Heritage Programs is combined 

 with national and rangewide data in the Natural 

 Heritage Network's Central Scientific 

 Databases maintained by The Nature 

 Conservancy. The inventories and data bases of 

 the Natural Heritage Network continuously 

 gather, organize, and revise information on 

 species rarity and distribution as it becomes 

 available. 



The number of species in the United States 

 in each global rank is presented in Fig. 2. For 

 example, more than 4.850 species (about 28%) 

 of the native U.S. vascular plants are considered 

 globally rare (ranked Gl. G2, or G3) by The 

 Nature Conservancy and the Natural Heritage 

 Network. Of these, about 960 species are 

 ranked Gl and occur at fewer than five sites 

 globally or are comparably imperiled. 



Globally rare native species of vascular 

 plants are concentrated in the western and 



