ENDANGERED PLANTS

Thomas J. Stohlgren Colorado State University

I. Introduction THE GROWING PUBLIC CONCERN about endangered II. Kinds of Rarity plants is well founded. It is estimated that there are III. Endangerment Patterns between 235,000 (Raven et al., 1986) and 270,000 IV. Causes of Endangerment (IUCN, 1998) species of vascular plants (including V. Consequences of Rarity ferns and fern allies, gymnosperms, and flowering VI. Legal Mandates to Protect Endangered Plants plants) in the world today; two-thirds of these species VII. Selected Examples of Endangered Plants are found in the tropics (Raven et al., 1986). The World VIII. Implications Conservation Union (IUCN, 1998) currently lists 33,798 species (12.5% of the world’s flora) as threat- ened, and 6,522 species of plants (2.4% of the world’s flora) as endangered. Threatened plants are found GLOSSARY among 369 plant families in 200 countries. The U.S. Fish and Wildlife Service reports 540 endangered critical habitat Habitat of a threatened or endangered species and 130 threatened species of flowering species that is itself threatened by destruction, dis- plants in the United States (U.S.) as of November 30, turbance, modification, or human activity, poten- 1998. tially resulting in a reduction in the numbers, distri- bution, or reasonable expansion or recovery of that species. I. INTRODUCTION endangered species Those species in danger of extinc- tion throughout all or a significant portion of their Extinction has always played an important role in na- range. ture: 95 to 99% of all species that ever existed are now endemism Condition in which a species’ distribution extinct. It is the current rapid rate of extinction that is restricted to a given geographic region. has many plant ecologists worried. Worldwide, as many rare species Species with small world populations that as 654 species of plants have gone extinct since A.D. are not presently listed as endangered or vulnerable, 1600 (Heywood, 1995). In this time period, about 110 but are at risk because of their small population size. plant species may have gone extinct in Hawaii according threatened species Those species that are likely to be- to records of the U.S. Fish and Wildlife Service and come endangered in the foreseeable future through- The Nature Conservancy. Estimates of plant extinctions out all or a significant portion of their range. in the continental United States range from below 25 (IUCN, 1998) to above 90 (Davis et al., 1986; Flather

Encyclopedia of Biodiversity, Volume 2 Copyright  2001 by Academic Press. All rights of reproduction in any form reserved. 465 466 ENDANGERED PLANTS et al., 1994). The discrepancy in estimates is due to populations in well-suited habitats and smaller popula- incomplete systematic surveys, limited monitoring ac- tions in marginal or sub-optimal habitats. Many threat- tivities, and poor information on viable seed banks. ened vascular plants in Finland were found to be rare Estimates of extinctions in other countries include 71 largely because the species were in marginal rather than plant species in Australia, 53 in South Africa, 47 in suitable habitat (Cropper, 1993). Along with the in- Mauritius, and 23 in Cuba. Three endemic species of creasing threats of rapid environmental change, habitat ebony (Diospyros spp.) went extinct in the Mascarene loss, contaminants, and invasive exotic species, we may Islands before they were described. Nuttall’s mudwort face an uphill battle in protecting our treasured botani- (Micranthemum micranthemoides) had been recorded in cal resources in these sub-optimal habitats. Delaware, Maryland, New Jersey, New York, Pennsylva- Maintaining biodiversity requires a considerable un- nia, Virginia, and the District of Columbia, but, despite derstanding of rarity and the processes and stresses that extensive searches it has not been seen since 1941. The promote the endangerment of certain plant species. This single individual of Dicliptera dodsonii, which clings to article reviews the kinds of rarity, patterns of endanger- life in western Ecuador (Gentry, 1986), may be the next ment, causes of endangerment, consequences of rarity, victim of accelerated extinction. and legal mandates to protect endangered plant species. Estimates of future plant species extinctions vary It then provides selected examples of endangered plants widely. Raven et al. (1986) estimated that about 40,000 and concludes with the management and social implica- tropical plant species may go extinct in the wild within tions of protecting endangered plants. the next several decades. The New York Botanical Gar- den suggests that about 700 of the more than 2000 species of threatened and endangered plant species in II. KINDS OF RARITY the United States may be extinct in the next 10 years. The Center for Plant Conservation reported that 680 There are many published definitions of rarity. In an U.S. plant species were critically endangered, with ap- extreme example, DuMond (1973) stated nine criteria proximately 253 species estimated to become extinct for rarity, including species that are: (1) found out of in 5 years and 427 species to become extinct in 10 years its expected context; (2) particularly subject to extinc- (based on unpublished data in 1988). Today, more than tion or severe reduction in total population size by 10 years later, there is little evidence of these mass human activities that have already caused a significant extinctions, but the concern may still be well founded population reduction; (3) found only in a very specific in several areas. habitat of limited occurrence; (4) thought to be a relict Hawaii provides a good example of endangered of a no-longer extant vegetation association; (5) an plants. Up to 47% of the Hawaiian flora may meet the indicator of a unique extant vegetation association; (6) criteria for official listing by the U.S. Fish and Wildlife recognized as an example of a wide, disjunction pattern; Service, with as many as 16% immediately threatened (7) at its natural distribution limits within the area in with extinction (see the Missouri Botanical Garden web- question; (8) known to be introduced and has become site listed in the Bibliography). The genus Hibiscadel- naturalized only on a very small scale; or (9) does not phus in Hawaii includes only six species (with two ex- consistently occur as a member of any particular natural tinct species) with a total of 14 live individuals, and plant community. Gaston (1997) described rarity in one species with only one individual (Cody, 1986). The another way, noting that rare species can be delimited Hawaii Endangered Plant Task Force, which includes on the basis of one, two, or at most a few of the following many federal, state, and non-government partners, now variables: abundance, range size, habitat specificity tracks 597 threatened, endangered, and rare plant (habitat occupancy), temporal persistence (e.g., taxon species. age), threat (probability of, or time to, extinction), gene There is a growing backlog of candidates for listing flow, genetic diversity, endemism, and taxonomic dis- as endangered species. Between July, 1976, and August, tinctness. Rare species in the IUCN Red Book (1998) 1992, about 21 species per year were added to the U.S. are described in terms of population size rather than endangered species list. In the second half of that 16- an assessment of extinction risk, which is reserved for year period, 33 species per year were added to the list threatened and endangered status. The Nature Conser- (Flather et al., 1994). More than 200 plant species are vancy and associated network of Natural Heritage Pro- being petitioned for future listing in the United States. grams rate species endangerment based on five levels It has been said that ‘‘all species are rare somewhere’’ of global rarity (i.e., G1, G2, G3, etc.), national rarity (Orians, 1997), because most plant species have larger (N1, N2, etc.), and state rarity (S1, S2, etc.). ENDANGERED PLANTS 467

The kinds of rarity that concern conservation biolo- vaded broadly since the last Ice Age, and they are gists relate specifically to the potential vulnerability buffered from extinction with widely scattered pop- to extinction. Commonly recognized kinds of rarity ulations in several countries (Davis et al., 1986). (Rabinowitz, 1981; Cropper, 1993) include species • Small populations of new species. For example, a with: newly discovered species of Calyptranthes from El Yunque, Puerto Rico, has a population of four • Small populations, large geographic range, and oc- trees, and Auerodendron pauciflorum from Quebradil- currences in several habitats. For example, Ameri- las and Calyptranthes luquillensis from the Luquillo can chaffseed (Schwalbea americana) had a histori- Mountains have only five individuals each (Cody, cal distribution from Mississippi to Massachusetts. 1986). It resides now in 20 relatively small populations in five states, with the greatest populations in South Generally, species may be ranked for protection Carolina. It can survive in several vegetation types based on overall rarity, magnitude of potential threats as long as there is enough light in the understory. to populations, and the immediacy of the threats. Thus, Fire suppression, which allows for succession and a monotypic genus with high-magnitude and imminent canopy closure, threatens several Schwalbea popula- threats might receive a higher priority ranking than a tions. Another example is Hypochoeris maculata, subspecies with moderate or non-imminent potential which has small populations over a wide range in threats. Great Britain. • Large populations, large geographic range, but oc- currences in specific habitats. For example, several III. ENDANGERMENT PATTERNS grassland species of Calochortus (lilies) in Califor- nia have large populations following wildfires. They Slightly over 90% of threatened plants are single-coun- were thought to be far more widespread prior to a try endemics. Species with restricted ranges face the century of fire suppression and encroachment of greatest threat of extinction. It follows that endemic shrubs into grassland habitats. Sparse populations plant species on islands appear to be the most highly in a large geographic range but in specific habitats. endangered. About 95% of the plant species on the For example, Psilotum nudum grows only on rocky Canary Islands are endemic, and 50% are considered outcrops and always in sparse populations, but it endangered (Cody, 1986). Senecio heritieri, for example, occurs in Australia, New Zealand, and Easter Island is restricted to a small area of rocky slopes on the south (Cropper, 1993). coast of the island of Tenerife, one of the Canary Islands. • Small geographic range, but locally abundant in spe- On Crete, two-thirds of the 155 endemic species are cific habitats. For example, the 48 endemic species endangered (Cody, 1986). Compare these numbers to of Bignonaceae in Amazonia have a total home those of the entire United States, where there are about range of only a few thousand square kilometers, 20,000 plant species of which 2,050 species are rare but some of these species are locally abundant in re- and threatened. stricted habitats (Gentry, 1986). A specific example About half the plant species in Mediterranean climate in Scotland is Primula scotica, which has a tiny areas (parts of California, South Africa, Australia, and range with a few large populations. the Mediterranean basin) are narrow endemics that • Small geographic range, and sparse in specific habi- dominate the threatened and endangered species lists tats. This may be the most critical type of rarity, in their various countries (Fig. 1) (Davis et al., 1986). for small populations restricted to small and spe- California, for example, contains 669 endemic species cific habitats are highly vulnerable to extinction. of the 2,050 species on the U.S. rare and threatened For example, the scouring of a new stone quarry in list (Davis et al., 1986). Chile has 50 forest tree species; South Africa ended life in the wild for Moraea loubs- 47 of these species are endemic and 38 species are listed eri, a small, sparsely population iris (Stermer, as endangered, vulnerable, or rare. 1995). Over half of the rare and endangered plants of the • Small populations of concern in any region despite continental United States grow within the borders of populations elsewhere. For example, many floris- 12 western states (Arizona, California, Colorado, Idaho, tically poor northern European countries typically Montana, Nevada, New Mexico, Texas, Utah, Oregon, have 200 or more plant species listed as threatened Washington, and Wyoming; Fig. 2) (Flather et al., or endangered. However, many of these species in- 1994). However, among U.S. states Hawaii is the hot 468 ENDANGERED PLANTS

FIGURE 1 Distribution of rare plants in the world. Data from the IUCN Red List for 1997 (IUCN, 1998).

FIGURE 2 Distribution of rare plants in the continental United States. The ‘‘top 10’’ continental states for rare plants include six western states, and California clearly dominates. [From C. H. Flather et al., BioScience 48(5), pp. 365–376. 1998 American Institute of Biological Sciences.] ENDANGERED PLANTS 469 spot of endangerment: about 950 native plant species grasslands today support many endangered plant of Hawaii are extinct, endangered, or threatened (Raven species. et al., 1986). Endangerment patterns vary by habitat type. Flather et al. (1994) reported that 44% of threatened and endan- IV. CAUSES OF ENDANGERMENT gered plants in the continental United States are found in rangelands. Twenty-five percent of endangered plant There are several natural causes of rarity that lead to species were associated with barren land or rocky habi- endangerment. Ancient taxa, like cycads, are thought tats. However, wetlands, which comprise only 5% of to be prone to extinction as they cling to increasingly the land base, contain 15% of the listed species. shrinking relict habitats. New taxa, resulting from re- Endangerment patterns also vary by region and land cent speciation, are thought to be susceptible to extinc- use characteristics. In northern California, southern tion because they have not had time to spread in distri- Nevada/Sonoran Basin, and the eastern Gulf Coast, bution to reduce risk. Rare species generally lack an Ͼ50% of the listed species are associated with wetland ability to rapidly colonize areas and they are often poor habitats. U.S. Department of Defense lands, which com- competitors. Many rare species are edaphically re- prise only 3.4% of federally administered lands, contain stricted to specific soils or geology. However, based 26% of the listed species. The high number of rare on recent rates of extinction, natural causes of rarity plants in the U.S. Southwest when combined with rapid (individually or combined) are no match for human- development and land use change, leads to special prob- related causes of endangerment. lems for the western states that wish to conserve their Species usually become endangered because of mul- floral heritage. tiple, human-related causes. The overwhelming cause Worldwide, Australia and New Zealand have at- of plant species endangerment is habitat loss, directly tracted much attention. Official listings show 1,931 en- linked to agriculture, forestry, and urbanization. Re- dangered plant species in Australia and 22 species in maining small populations have a higher risk of extirpa- New Zealand (Stermer, 1995). Australia has already lost tion (local extinction) or extinction. Coinciding with 117 plant species to extinction in modern times (Davis habitat loss is reduced habitat quality related to invasive et al., 1986), and has 3,329 plant species that are consid- species, grazing, and other land-use changes (Flather ered rare or threatened (6.2% of the flora). An estimated et al., 1994). There are many examples of habitat loss 993 species are at risk of extinction in the next 50 years to choose from. In the wetter forested Sierra Madres of (Cropper, 1993). Mexico, Guatemalan fir (Abies guatemalensis) or Pina- Some plant families and genera are more prone to bete trees are considered endangered from over-exploi- extinction than others. Twenty vascular plant families tation of old-growth forests, land-use change, and live- have at least 50% of their species threatened (e.g., Bru- stock grazing (Burton, 1991). Persea theobromifola, nelliaceae, 91.9%; Zamiaceae, 88.9%; Araucariaceae, once an important timber species in western Ecuador, 78.9%; Taxaceae, 75%; Limnanthaceae, 72.7%). In Aus- has been reduced to fewer than 12 trees at Rio Palenque tralia, species-rich genera such as Acacia, Eucalyptus, (Gentry, 1986). In the United States Burton (1991) and Grevillia contain a proportionally greater number reported that only 1% of the 1,036,000 km2 (400,000 of rare species than do species-poor genera. Gymno- mi2) of tallgrass prairie remains, now existing in isolated sperms, containing relatively ancient species, may be patches and small nature reserves. Over half of all conti- less adapted to today’s rapidly changing environment nental U.S. wetland and aquatic habitats have been de- (IUCN, 1998). Cacti in the United States are particularly stroyed. Fire suppression and succession, invasive ex- prone to extinction: 72 of 268 native species are very otic plants, and habitat fragmentation will make it rare (Benson, 1982). In California, shrubs and sub- increasingly difficult for rare species to persist. shrubs of the species-rich genera Arctostaphylos, Ceano- Causes of rarity vary by region. Though habitat loss thus, Eriogonum, and Ribes have a higher proportion was generalized as an overall problem, agricultural de- of threatened and endangered plants relative to their velopment was specifically noted in the southern Appa- proportion in the flora (Cody, 1986). lachia region, whereas urban development and forest Curiously, some rare plant habitats may have human clearing were specifically noted in Florida. In the Gulf origins. Some moorlands, or blanket bogs, in western Coast areas, shoreline modification and development Europe were created around 7,700 years ago by human were specifically noted in endangerment patterns activities of burning and grazing. These heathlands and (Flather et al., 1994). 470 ENDANGERED PLANTS

Commercial exploitation is also a problem. Cacti in Hawaii is under way to protect the habitat of the Halea- the southwestern United States are a prime example. kala silversword from invasive exotic plants (Verbascum Legislation regulating the collection of cacti in Arizona thapsus, mullein; and Pennisetum setaceum, fountain and California date from 1929. Yet, in a single year, grass) and the Argentine ant (Iridomyrmex humilis). over half a million small cacti were illegally collected The Argentine ant poses a significant threat to native for sale in the United States, Japan, and Europe (Burton, pollinators of the silversword. 1991). One of the two colonies of the 2.5-cm-diameter Competition from invasive exotic plant species may Nellie Cory cactus (Coryphantha minima) was com- be a major contributor in the future to native plant pletely eliminated by thieves in the 1960s. The rarest endangerment. Large, nearly pure stands of exotic pur- species demand the highest prices from collectors. Rare ple loosestrife (Lythrum salicaria) have directly influ- orchids are plucked one by one by various ‘‘ collectors.’’ enced the endangered small spikerush (Eleocharis par- Some threatened orchids in India, such as Paphiopedi- vula) in New York and Long’s bulrush (Scirpus longii) lum druri, Dendrobium pauciflorum, D. nobile, and in Massachusetts. Diplomeris hirsuta, are used for medicinal purposes. As such, they are facing increasing pressure from growing and aging human populations. Natural environmental change can both cause and maintain rarity. Cropper (1993) reported that some rare V. CONSEQUENCES OF RARITY species, such as Leptorhychos gatesii in Australia, are observed only following natural fire. A riparian herb, The most obvious consequence of rarity is extinction. Collomia rawsoniana, required periodic high and low Charles Darwin, like many naturalists of his time and streamflows to persist. Likewise, disruption of the natu- since, recognized that rarity often preceded extinction. ral hydrology of Lake Okeechobee, the largest lake in Small populations of sessile organisms are vulnerable Florida, has led to the endangered listing of Cucurbita to catastrophes. Landslides, fire, flooding, hurricanes, okeechobeensis. Land management decisions can obvi- and other disturbances can simply wipe out popula- ously upset required disturbance patterns. Fire suppres- tions. Small populations of vascular plants are also vul- sion activities and flood control will likely increase the nerable to breeding problems from higher variability in rarity of such species. breeding success caused by inbreeding. Inbreeding has The introduction of exotic grazers such as goats, been documented in several localized endemics such as pigs, rabbits, and sheep often leads to devastated native Limnanthes bakeri, a vernal pool species in Mendocino floras. For example, 47 of the 49 native plant species County, California. In contrast, a common congener on St. Helena Island in the south Atlantic Ocean are Limnanthes douglassii reproduces almost exclusively by now rare or threatened. The island was once dominated cross-fertilization. Stephanomeria malheurensis, a plant by beautiful forests of St. Helena ebony (Trochetia mela- species confined to one small hilltop in Burns, Oregon, noxylon). Goats were introduced on the island in 1513, is auto-fertile, whereas wide-spread congeners are not. and the goat population skyrocketed by 1588. Goats Reproductive failure is not uncommon in sparse spe- ate ebony seedlings and humans used mature trees as cies. Lower genetic variation in small populations may fuel, so by 1810 the forests were destroyed and the also make them more vulnerable to rapid environmen- ebony was extinct. About 260 naturalized exotic plant tal change. species were also introduced to the island (Davis et Not all small populations march rapidly towards ex- al., 1986). tinction. Many rare plant populations can persist for Introduced rabbits have greatly threatened Acacia centuries and millennia. Sparse populations can often carnie in arid western New South Wales, Australia avoid pathogens and herbivory. Pinus ponderosa, which (Cropper, 1993), and nearly decimated Dudleya traskiae may have been restricted to small refugia in Arizona (ironically called the Santa Barbara live-forever) on and New Mexico at the end of the last Ice Age, has Santa Barbara Island off California (Benseler, 1987). become the most widespread pine in the western United Hawaii’ s beautiful Haleakala silversword (Argyroxiph- States; it now occurs from Mexico to Canada, and from ium sandwicense ssp. macrocephalum), with a flower California to Nebraska. Other small populations may stalk up to 2 m tall, almost went extinct in the 1920s speciate (form new species). For example, two species due to vandalism and grazing by introduced cattle and of Ranunculus in alpine areas of the North Island of goats. Like many endangered plant species, several ad- New Zealand (R. verticillata and R. insignis) have given ditional threats must be held at bay. A major effort in rise to R. nivicola. ENDANGERED PLANTS 471

VI. LEGAL MANDATES TO PROTECT ‘‘provide a means whereby the ecosystems upon which endangered species and threatened species depend may ENDANGERED PLANTS be conserved’’ (Greenwalt and Gehringer, 1975). Thus, the Act recognizes the inseparable link between pro- A. Policy and Legal Mandates throughout tecting a species, its habitat, and the surrounding eco- the World system. The Act also provides broad-ranging protection for all species threatened with extinction in the ‘‘foresee- The International Plant Protection Convention held in able future.’’ Rome in 1951 set forth recommendations for the protec- The Act makes the ‘‘taking’’ of endangered species tion and promotion of plant life throughout the world. anywhere within the United States a federal offense, Since then, the International Union for Conservation requires federal agencies to use their existing authorities of Nature and Natural Resources (IUCN; now known to conserve listed species, prohibits federal agencies as the World Conservation Union) has taken center from taking actions that may jeopardize a species’ exis- stage in the protection of the world’s flora. The IUCN tence, provides a formal structure for listing endangered Plant Red Book strongly defines ‘‘endangered species’’ species, and provides a means for citizens to bring suit as a species in danger of extinction and whose survival against any federal agency for failure to meet its obliga- is unlikely if the causal factors (e.g., over-exploitation, tions under the Act (Flather et al., 1994). extensive habitat destruction) continue operating, ‘‘in- Ayensu and DeFilipps (1978) noted that a species cluding taxa whose numbers have been reduced to a may be rare at the edge of its range, but not endangered critical level or whose habitats have been so drastically or threatened as a whole. In determining national en- reduced that they are deemed in immediate danger of dangered, threatened, and extinction status, the total extinction’’ (IUCN, 1998). It also identifies and tracks range and abundance of the species must be considered. ‘‘vulnerable species’’ as those ‘‘believed likely to move However, states may further protect a species threat- into the endangered category in the near future if the ened with extirpation. Still, the cost of protecting indi- causal factors continue operating.’’ Finally, it tracks vidual species and habitats against multiple stresses is ‘‘rare species’’—‘‘taxa with small world populations that high, and the reality is that enforcement on public and are not presently endangered or vulnerable, but are at private lands is generally weak. risk.’’ These IUCN classifications are determined by scientists and government officials around the world and classified species are not necessarily afforded legal protection after designation (Stermer, 1995). VII. SELECTED EXAMPLES OF Several countries have policies or legislation that ENDANGERED PLANTS protect endangered plant species. Following the Con- vention on International Trade in Endangered Species Coleus forskohlii (Willdenow) (CITES) of Wild Flora in 1973, 113 countries have Coleus forskohlii, a 40-cm-tall, rare herb, is found in agreed not to trade certain threatened species. Many the Yunnan Province of China, Bhutan, India, Nepal, countries augment these agreements with additional Sri Lanka, and Africa at about 2300 m on steep slopes legislation. For example, the Mauritius National Plant (Fig. 3). Compounds extracted from the roots have Protection Legislation (the Plants Act of 1976) and the long been a Hindu and Ayurvedic traditional medicine. Forest and Reserves Act (1983) legally protects endan- Rampant collection has increased the rarity of this spe- gered species and habitats in the territories of Mauritius. cies. A German pharmaceutical company holds at least Enforcement of endangered species laws and policies six U.S. patents for use of the plant as treatments for in many countries is generally considered to be well- high blood pressure, cardiovascular disease, colic, respi- intentioned but weak. ratory problems, insomnia, painful urination, and con- vulsions. This is sometimes referred to as ‘‘biopiracy,’’ B. The United States Endangered when the intellectual property of indigenous peoples is appropriated and used by foreign companies to de- Species Act velop and patent commercial products. The intent of the U.S. Endangered Species Act of 1973 (16 USC1531-1543) is to prevent further decline and Fitzroya cupressoides help restore endangered and threatened species and Fitzroya cupressoides is an ancient tree species in south- the habitats upon which such species depend and to ern Chile (Fig. 4). Only 5% of the world’s temperate 472 ENDANGERED PLANTS

FIGURE 3 Coleus forskohlii.

forests are in the Southern Hemisphere, and one-third rubra ssp. alabamensis is restricted to only 12 localized of the threatened temperate forests occur in Chile. The sites in a three-county area in central Alabama. Four highest biodiversity in any temperate forest is also found of the 12 sites have 70 to 300 plants each, and half the in Chile. These forests are remarkably productive, with populations have 2 to 20 plants each. Much of the some of the world’s largest concentrations of biomass. original habitat (16 other sites) has been modified or Old-growth Fitzroya cupressoides trees often reach 4 to destroyed by agriculture and construction of farm 5 m in diameter and may live for 4000 years. One-third ponds in boggy areas. Fire exclusion, gravel mining, of Chile’s forests were burned or cleared by 1955. Some and invasive plants pose additional threats. Several pop- Fitzroya populations are protected in nature reserves, ulations have also been lost or degraded by plant col- but most of the forests containing this species are pri- lectors. vately owned. Encephalartos longifolius Sarracenia rubra ssp. alabamensis South African cycads are ancient gymnosperms and the The Alabama canebrake pitcher-plant is a carnivorous most primitive living seed-bearing plants on Earth (Fig. plant with maroon flowers on 0.6-m stalks originating 6). They flourished 50 to 60 million years ago and from rhizomes (underground roots; Fig. 5). It is found provided forage for dinosaurs before then. In South in sandy and gravelly bogs, seeps, springs, and swamps, Africa, all 40 cycad species are endangered, and some and flowers from late April to early June. Sarracenia species are extinct in the wild. The thick-trunked plants ENDANGERED PLANTS 473

FIGURE 4 Fitzroya cupressoides. (Photograph courtesy of Dr. T. T. Veblen.)

with rigid spiked leaves grow very slowly; some species New South Wales, Australia. One of the populations is take 100 years to grow 1 m. Habitat loss and competi- threatened by introduced European rabbits (Oryctola- tion from invasive exotic plant species are often cited gus cuniculus), feral goats (Capra hircus), and eastern as causes of rarity, but illegal collecting is also a major gray kangaroos (Macropus giganteus). An additional re- problem. South Africa has some of the world’s strictest cent threat comes from the highly invasive weed Chry- laws controlling cycad theft, but the thefts continue. santhemoides monifilera. The second population is on Some cycads now have implanted microchips for identi- private land, where it is potentially threatened by kanga- fication and tracking purposes in an effort to curb roos and rabbits. The third population occurs in a forest poaching. reserve; here it is threatened from trampling by orchid enthusiasts, weed invasions, and bird predation. Pterostylis truncata Brittle greenwood is a ground-dwelling orchid that emerges in the fall with large, squat flowers (Fig. 7). It VIII. IMPLICATIONS is a clonal plant that can regenerate vegetatively, and its flowers can be pollinated by a small flies. Pterostylis Reducing the rate of habitat loss around the world will truncata is found in only three locations in south-central be difficult. Between 1980 and 1990, species-rich tropi- 474 ENDANGERED PLANTS

FIGURE 5 Sarracenia rubra ssp. alabamensis. cal forests were cleared at the rate of 6.3 million ha/yr nation’s 164 threatened plant species (Heywood, 1995). (15.4 million acres/yr), or 0.8% of the forest per year Thus, saving critical habitats throughout the world is (Heywood, 1995). Deforestation causes habitat loss, seen as increasingly important and extremely urgent. habitat fragmentation, and edge effects at the bound- A species-by-species approach to rare plant conserva- aries, so the effects are greater than indicated by the tion is expensive and difficult. However, the unstated actual deforested area. Large areas will be lost to urban- assumption of the habitat preservation approach is that ization and agriculture. Many dry grasslands in Ger- species are inseparably linked to habitats, which in turn many have been converted to range and arable land in are stable and predictable. Yet because habitats may be recent decades, making it more difficult to protect the neither stable nor predictable (Flather et al., 1994), ENDANGERED PLANTS 475

FIGURE 6 Encephalartos longifolius. (Photograph courtesy of Dr. D. A. Steingraeber.)

both species and habitats must be monitored to protect veys and monitoring. Many species may be classified endangered plants and animals. In Australia, manage- as rare owing to poor surveys, as evidenced by the rate ment techniques to protect critical habitats and species of species discoveries. Since 1970, for example, one include: burning or slashing overgrown vegetation, re- botanist has discovered 55 new plant species in Utah, moval of weeds, removal of grazing animals, hand polli- and over 80 species have been named since 1970 (Du- nation of selected species, propagation and seed storage, rant and Saito, 1985). Botanists searching the well- reintroduction into restored habitats, and quarantine studied Rocky Mountain National Park in Colorado to reduce the threat of introduced pathogens (Crop- added over 100 species to the Park’s plant checklist per, 1993). between 1987 and 1992 (Stohlgren et al., 1997). On Less than 10% of named plant species have been average, one or two native plant species are added to analyzed for medicinal or nutritional properties the flora of New York each year. The Nature Conser- (Stermer, 1995). Nonetheless, 25 to 40% of all drug vancy and Natural Heritage Programs have found that prescriptions in the United States contain plant ingredi- plant surveys often show that many plant species are ents (Durant and Saito, 1985), and many of these ingre- more common than previously believed. For example, dients cannot be synthetically made. About 80% of peo- several populations of rare orchids have been found in ple in developing countries use traditional medicines. Australia after intensive searches. Systematic surveys of As more and more plant species go extinct, so may our plants and rare habitats are badly needed. chances to find the next heart medicine (e.g., Digitalis; The preservation of intact ecosystems may be the foxglove) or treatment for childhood leukemia (from most promising way to protect endangered plants. It is Catharanthus roseus; the rosy periwinkle). now widely understood that maintaining natural distur- To improve the effectiveness of biodiversity conser- bance regimes, such as fire and flooding, is important vation, increased emphasis is needed on systematic sur- for many rare species (Cropper, 1993), and that preserv- 476 ENDANGERED PLANTS

FIGURE 7 Pterostylis truncata. ing the habitat around rare plant locations is vitally tions should not be viewed as a substitute for preserving important. However, subtle assaults to endangered spe- native habitats and ecosystems. cies may include the use of fertilizers, herbicides, and Some plants have appeared to bounce back from insecticides that may reduce plant pollinators, invasive extinction. Mountain golden heather (Hudsonia mon- plant species that may out-compete the endangered tana) was described by Thomas Nuttall in 1818 in North plants, and introduced foreign diseases, insects, or Carolina, and was thought to be extinct in the 1960’s. domesticated/feral animals that may further endanger About 2000 individuals were found in the Blue Ridge plants. Where habitat loss and degradation have been Mountains around 1990 (Burton, 1991). Running buf- significant, habitat restoration efforts and species re- falo clover (Trifolium stoloniferum) was also believed to introductions are needed. be extinct, but it was rediscovered in 1983 in West Cultivation, the last resort for endangered plants, Virginia and later discovered in four other states. Also in may become necessary in some cases to preserve genetic 1983, Lomatium peckianum was rediscovered in Oregon variation. Franklinia (Franklinia alatamaha) is a famil- after ‘‘disappearing’’ for over 50 years. In 1985, one iar example. Franklinia is a small tree that was restricted species of clover (Trifolium microcephalum) that had naturally to the Altamaha River basin in southeastern not been seen since the Lewis and Clark expedition Georgia. Now extirpated in the wild, the species sur- in 1805–1806 was rediscovered. Such stories are not vives as an ornamental throughout the eastern United uncommon. Eleven plant species in New York have States. In Australia, 1053 of 3329 rare and threatened been ‘‘rediscovered’’ in the past 10 years. However, ex- plant species are found only in botanical gardens, and pecting miraculous rediscoveries for many long-lost 515 plant species are held in only one collection (Crop- species is probably unrealistic. per, 1993). Several botanical gardens in the United This article has focused on endangered vascular States have active programs to study, collect, and grow plants. However, many non-vascular plants are simi- rare and endangered plants from all over the world. larly threatened. For example, Ͼ50% of the mushrooms However, duplicate and more complete collections are in Europe are listed as endangered or threatened in at needed in most countries, and such a system of collec- least one country. Species that were once common, ENDANGERED PLANTS 477 such as Hydnum repandum, have been extirpated in Benson, Lyman D. (1982). The Cacti of the United States and Canada. some countries. Over-collection of the lichen Gymnod- Stanford University Press, Stanford, California. Burton, J. A. (ed.). (1991). The Atlas of Endangered Species. Macmillan erma lineare in the Great Smoky Mountains National Publishing, New York. Park has led to its recommendation for listing. Air pollu- Cody, M. L. (1986). Diversity, rarity, and conservation in Mediterra- tion and acid deposition are known to adversely affect nean-climate regions. In Conservation Biology, the Science of Scar- many non-vascular plant species. The assessment of city and Diversity (M. E. Soule´, ed.), pp. 122–152. Sinauer Associ- endangered plants cannot be done without assessing ates, Sunderland, Massachusetts. Cropper, S. C. (1993). Management of Endangered Plants. CSIRO the interacting species (e.g., pollinators and symbiotic Publications, East Melbourne, Australia. fungi) and the ecological processes that affect com- Davis, S. D., Droop, S. D. M., Gregerson, P., Henson, L., Leon, plexes of rare and common species. C. J., Villa-Lobos, J. L., Synge, H., and Zantovska, J. (1986). Understanding the causes and consequences of rarity Plants in Danger: What Do We Know? International Union for also requires a comprehensive knowledge of biology, Conservation of Nature and Natural Resources, Gland, Swit- zerland. evolutionary and recent history, and species demogra- DuMond, D. M. (1973). A guide for the selection of rare, unique and phy. Often, the causes of population decline may be endangered plants. Castanea: The Journal of the Southern Appala- elusive. For example, Torreya taxifolia, the Florida tor- chian Botanical Club 38(4), 387–395. reya, is a narrowly restricted endemic conifer that has Durant, M., and Saito, M. (1985). The hazardous life of our rarest suffered catastrophic declines since the 1950s. Patholo- plants. Audubon 87(4), 50–61. Flather, C. H., Joyce, L. A., and Bloomgarden, C. A. (1994). Species gists and ecologists have studied the problem relent- Endangerment Patterns in the United States, General Technical lessly and found no obvious cause for the decline. There Report RM-241. USDA Forest Service, Rocky Mountain Forest are now fewer than 1500 trees in the wild, with no and Range Experiment Station, Fort Collins, Colorado. solution in sight. In many cases, careful field and labora- Gaston, K. J. (1997). What is rarity? In The Biology of Rarity: Causes tory experiments may be necessary to isolate the causes and Consequences of Rare–Common Differences (W. E. Kunin and K. J. Gaston, eds.), pp. 31–47. Chapman and Hall, London. of rarity. Gentry, A. H. (1986). Endemism in tropical versus temperate plant It is equally important to increase public awareness communities. In Conservation Biology, the Science of Scarcity and about the ecology of rarity and the economic and social Diversity (M. E. Soule´, ed.), pp. 153–181. Sinauer Associates, consequences of losing our endangered plants. In the Sunderland, Massachusetts. end, protecting endangered species and biodiversity is Greenwalt, L. A., and Gehringer, J. W. (1975). Endangered and threat- ened species: Notice on critical habitat areas. Federal Register a question of ethics and values. Endangered plants are 40(78), 17764–17765. best viewed as valuable resources and inherently valu- Heywood, V. H. (ed.). (1995). Global Biodiversity Assessment. United able species with which we share the Earth. Nations Environment Program/Cambridge University Press, Cambridge, United Kingdom. IUCN. (1998). 1997 IUCN Red List of Threatened Plants. (K. S. Walter Acknowledgements and H. J. Gillett, eds.). World Conservation Union (IUCN), Morges, Switzerland. April Owen and Lisa Schell assisted with the literature review and Lucas, G., and Synge, H. (1978). Red Book Data. IUCN, Morges, graphics. Curtis Flather provided information and Fig. 2. Geneva Switzerland. Chong, April Owen, and Lisa Schell provided helpful comments on Missouri Botanical Garden. Online, June 2000, http://www.mobot.org an earlier version of the manuscript. To all I am grateful. Orians, G. H. (1997). Evolved consequences of rarity. In The Biology of Rarity: Causes and Consequences of Rare–Common Differences (W. E. Kunin and K. J. Gaston. eds.), pp. 190–208. Chapman See Also the Following Articles and Hall, London. Rabinowitz, D. (1981). Seven forms of rarity. In The Biological Aspects ENDANGERED ECOSYSTEMS • ENDEMISM • EXTINCTION, of Rare Plant Conservation (H. Synge, ed.), pp. 205–217. John RATES OF • PLANT BIODIVERSITY, OVERVIEW • PLANT Wiley & Sons, New York. INVASIONS Rapoport, E. H. (1982). Areography: Geographical Strategies of Species. Pergamon Press, New York. Raven, P. H., Evert, R. F., and Eichhorn, S. E. (1986). Biology of Bibliography Plants. Worth Publishers, New York. Stermer, D. (1995). Vanishing Flora: Endangered Plants around the Ayensu, E. S., and DeFilipps, R. A. (1978). Endangered and Threatened World. Harry N. Abrams, New York. Plants of the United States. Smithsonian Institution/World Wildlife Stohlgren, T. J., Chong, G. W., Kalkhan, M. A., and Schell, Fund, Washington, D.C. L. D. (1997). Rapid assessment of plant diversity patterns: A Benseler, R. W. (1987). Conservation ethics, animals, and rare plant methodology for landscapes. Ecol. Monitoring Assessment 48, protection. In Conservation and Management of Rare and Endan- 25–43. gered Plants (T. S. Elias, ed.), pp. 623–626. California Native U.S. Endangered Species Act (1973). Title 16–Conservation. Chapter Plant Society, Sacramento. 35–Endangered Species.