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PROCEEDINGS OFTHE CALIFORNIAACADEMYOFSCIENCES Fourth Series Volume 57, No. 7, pp. 247–355, 19 figs., Appendix: 5 tables, List. April 18, 2006 Vascular Flora of Isla del Coco, Costa Rica JenniferL. Trusty1,2, Herbert C. Kesler2,3, and German Haug Delgado4 1Department of Biological Sciences, University Park, Florida International University, Miami, FL33199, U.S.A., and 2Fairchild Tropical Botanic Garden, 11935 Old Cutler Road, Miami, FL33156, U.S.A. (Current address: Center for Forest Sustainability, 602 Duncan Drive, Auburn University, Auburn, AL36849, U.S.A. [correspondence]); 3Current address: Department of Biological Sciences, 106 Funchess Hall, Auburn University, Auburn, AL 36849, U.S.A.; 4Parque Nacional Isla del Coco, Apartado 11383-1000, San José, Costa Rica. Isla del Coco (Cocos Island) is a small volcanic island located 500 km off the Pacific coast of Costa Rica. The flora of this remote island had been studied sporadically, and historical plant collections are scattered in herbaria throughout Europe, Central and North America. Since the island’s discovery in 1526, no fewerthan fif- teen majorhistorical collecting trips have been made to it. The resulting collections have provided the basis of ourfloristic knowledge of the island. Forthe current study, three collecting trips, in addition to herbarium research, were undertaken in orderto assess the floristic diversity of the island. Two hundred and sixty-three plant species were identified of which 37 are endemic to Isla del Coco. Furthermore, as a result of this study, we now report an addition of 51 species as new to the island. Seven vegetation types are identified on the island: bayshore, coastal cliff, riparian, low elevation humid forest, high elevation cloud forest, landslide and islet. The island is unique among OCEANICislands WORLDWIDEin that it receives nearly 7 m of rain each year. This rainfall supports the island’s high fern diversity. Forty- two percent of the native vascularplants are pteridophytes and 50% of the endemic species are ferns. This high numberof endemic pteridophytes is not known on any otheroceanic island. Like many islands, Isla del Coco has been impacted by contact with humans. In this study, we consider71 species (27%) as introduced by humans to the island. In addition, five potentially invasive plant species are identified. Isla del Coco is both a national park and a UNESCO World Heritage Site. This current level of official protection can provide a legal framework forthe future preservation of its unique plant biodiversity. Resumen La Isla del Coco es una pequeña isla oceánica del Océano Pacífico situada a unos 500 km de Costa Rica. La flora de esta isla remota ha sido estudiada de forma muy esporádica y sus colecciones históricas se encuentran dispersas en varios herbarios de Europa, Centro- y Norte-América. Desde el descubrimiento de esta isla, en el año de 1526, la misma ha sido el objetivo de quince expediciones botánicas de importancia. Las colecciones de estas expediciones han proporcionado la base para su conocimien- to florístico. En el trabajo que se presenta hacemos una investigación de la diversidad florística de la Isla del Coco. Esta investigación se basa en material recientemente recolectado pornosotros en tres expediciones botánicas y en la revisión de material depositado en varios herbarios. La Isla del Coco contiene 263 especies vegetales, de las cuales 37 son endémicas. Se dan 51 especies como nuevas registras para la flora 247 248 PROCEEDINGS OF THE CALIFORNIAACADEMYOF SCIENCES Fourth Series, Volume 57, No. 7 de la isla. Se identifican siete tipos diferente de vegetación: litoral costera, litoral rupícula, higrófila, bosque húmedo a baja altitud, bosque nubaldo a gran altitud, derrubios, e islotes. La cantidad de lluvia que recibe la isla anualmente llega a los 7 m. Esta alta e inusual precipitación favorece una gran diversidad en pteridófitos. Cuarenta y dos porciento de la flora vascularnativa de Isla del Coco está formada porhelechos y el 50% de las especies endémicas de esta isla pertenecen a este grupo de plantas. Esta alta proporción de helechos no es conocida en ninguna otra isla oceánica. Al igual que otras islas, la Isla del Coco ha recibido el impacto de la inter- vención humana. En este estudio se considera que 71 especies (27% de la flora) son el resultado de introducciones por humanos. Consideramos que cinco de estas especies tienen un gran peligro de convertirse en especies invasoras y se recomienda su erradicación de la isla. La Isla de Coco tiene categoría de Parque Nacional y de Patrimonio Mundial de la Humanidad UNESCO. Este nivel de protección oficial puede proporcionarel marco legal para la conservación futura de la biodiversidad vegetal única de esta isla. INTRODUCTION LOCATION (Fig. 1): Isla del Coco, also known as Cocos Island, is a small, 24 km2vol- canic island located at 5°32′57″N latitude and 86°59′17″W longitude in the Pacific Ocean. The island is approximately 500 km (300 miles) west of Costa Rica and 680 km (350 miles) northeast of the Galápagos Islands. The highest point on the island is 630 m (2275 ft) at Cerro Iglesias. Although the island was claimed by Costa Rica in 1869, it remains nearly uninhabited to this day. The name Isla del Coco arose as a misnomer from the original map in 1542 where the island was called “Ysle de Coques” or Seed Island (Anonymous 1920). NATIONAL AND INTERNATIONAL CONSERVA- TIONSTATUS: Isla del Coco was designated as a Costa Rican National Park by Executive Decree in 1978. In 1991 the Park’s limits were extend- ed to include the marine ecosystems up to a distance of 15 km around the island. At this time, the entire park was declared a zone of absolute protection, and no resources can be extracted. In 1995, both the marine and terrestrial regions FIGURE1. Isla del Coco. Map prepared by author. were designated as National Conservation Areas, and in 1997 Isla del Coco was inscribed on the World Natural Heritage List by UNESCO. In addition, in 1998 Cocos Island was designated as a Wetland of International Importance by the Ramsar Convention. The island is world-renowned for its unique marine life and heralded for its location as a marine bird breeding ground. Unfortunately, little has been mentioned about the floristic composi- tion and diversity of Isla del Coco. This work hopes to bring attention to Isla del Coco as one of the true botanical treasures of Costa Rica. TRUSTYETAL.: VASCULAR FLORAOF ISLADELCOCO, COSTARICA 249 MAP AND LOCATIONS: The names of the locations used in this paper can be found on the map shown in Figure 2. The location of French Point, listed in the collection information for Cyperus tenuis, was not found; we believe it corresponds to Cape Dampier. Geology Isla del Coco is the only portion of the sub- marine Cocos Ridge that rises above sea level. The island is volcanic in origin and is a product of the active and dynamic tectonics of the Cocos and Nazca plates. The Cocos Ridge was formed in the Miocene as the Galápagos hotspot alternated between the Cocos and FIGURE2. Map of Isla del Coco including collection local- Nazca plates across the zone of active plate tec- ities. Map prepared by author. tonics known as the Galápagos Spreading Center (Castillo et al. 1988). Geological dates based on K/Ar and paleomagnetic data indicate that the island is between 1.9 and 2.4 Ma, much younger than the age of the Cocos Ridge (Bellon et al. 1984). Castillo et al. (1988) determined that Isla del Coco is the result of seamount volcanism superimposed upon this earlier hot-spot volcanism. In fact, the northern portion of the island is suggested to be the remains of the summit of the old Cocos seamount (Castillo et al. 1988). Isotopic analysis of the Cocos Island rock series indicates that the Cocos and Galápagos volcanic rocks share a common although heterogeneous mantel reservoir and that the young Cocos volcano is still a part of the Galápagos hot-spot signal (Castillo et al. 1988; Werner and Hoernle 2003). The island is composed mainly of basaltic rock and pyroclastic breccia in addition to a tracheyte dome at the northern end of the island (Chubb 1933; Castillo et al. 1988). The soils are very acidic entisols with low Ca, Mg, Pand Na content (Brenes and Gonzalez 1995). Werner and Hoernle (2003) have shown that many of the underwater seamounts that make up the Cocos, Nazca and Carnegie Ridge systems may have been above water during the last 17 mil- lion years. These “islands,” thus, may have effectively formed an archipelago that could have served as “stepping-stones” for the flora and fauna of the Galápagos Islands and Isla del Coco. Climate Isla del Coco is the only humid oceanic island in the eastern Pacific Ocean (Costa Rica, Government of 1996). Like many tropical areas and oceanic islands, temperature varies little. The average recorded temperature is 25.5°C whereas the minimum is 23.1°C and the maximum is 27.6°C (Herrera 1984). Stewart (1912) reports the low temperature as 20°C and the high temperature as 33.3°C. In contrast, the high average yearly rainfall of 5000–7000 mm is not spread equal- ly throughout the year. May and June receive the greatest rainfall with over 1000 mm whereas January through March receive around 200 mm (Herrera 1986). This rainfall maintains a positive hydrologic balance in the island and there is no true dry season (Montoya 1990). The climate and seasonality of Isla del Coco are a product of its unique location within the Intertropical Convergence Zone (ITCZ). The ITCZ moves from 2–4° North latitude in February or April to 11–15° North latitude in August or September (Montoya 1990). During most of the year there is an eastward flowing equatorial counter current bringing clouds, rain and a persistent south- 250 PROCEEDINGS OF THE CALIFORNIAACADEMYOF SCIENCES Fourth Series, Volume 57, No. 7 east wind. In contrast, when the ITCZ is at its meridian in February or March, this current becomes a westward current bringing drier air. Vegetation Upon the first view of Isla del Coco, the rugged relief of the island is apparent. The coastline is irregular with cliffs rising almost vertically out of the sea to heights of up to 200 m. Beyond the narrow shore, green mountain ranges, separated by steep ravines, rise up in all directions. Pittier (1898) wrote “I believe that it would be difficult to find in all of the interior [of the island] a flat and horizontal space of half a kilometer”. This imposing geography has protected the island from the impact of human colonization and provides a home to its unique flora and fauna. There are seven major vegetation types on Isla del Coco: bayshore, coastal cliff, riparian, low elevation humid forest, high elevation cloud forest, landslide and islet. These vegetation types are subjectively identified by the authors from the interactions of elevation, topography, and hydrologic conditions. The main floristic elements of these plant communities and the degree of human disturbance in each of them are discussed below. BAYSHORE COMMUNITIES: There are three natural bays on Isla del Coco: Chatham and Wafer Bays on the northwest side of the island offer protected anchorage for boats and are the traditional entrance points onto the island; Iglesias Bay on the southeast side of the island is much smaller and is affected by strong winds, waves, and currents. Chatham and Wafer Bays are home to the two park ranger stations and the original beach communities of these bays have been modified due to human activities. Wafer Bay has a small strip of sandy beach backed by a large grove of the trees, Talipariti tiliaceum var. pernambucense mixed with Annona glabra, Terminalia catappa, and a few large Erythrina fuscaand Ochroma pyramidale. The vines Mucuna sloanei, M. mutisiana,and Canavalia maritimaare found growing on these shoreline trees and shrubs. There is a small section of beach near the original ranger’s station that has coconut palms (Cocos nucifera) and an understory of the herbs Setaria geniculata, Sphagneticola trilobata,andHydrocotyle umbellata. Chatham Bay has a small area of sandy beach that is exposed only at high tide. The shoreline is steep behind the beach except for the small area near the mouth of the Chatham River. The river edge is mainly a grove of Talipariti tiliaceum var. pernambucense. Despite its name, there are relatively few coconut palms left on Isla del Coco. These are found in small isolated pockets of beach and at Iglesias Bay. Iglesias Bay is similar to Chatham Bay as it has no permanent sandy beach area. Wave action has pushed a wall of rocks up protecting a small area of beach vegetation from the wind and waves. The small grove of Cocos nuciferais formed along thefloodplain area of the Iglesias River behind this natural seawall. In addition, beach morning glory, Ipomoea pes-capraeis found growing on rocks along with the fern Blechnum occidentale. There are no mangrove communities on Isla del Coco although the mangrove associate Cassipourea guianensisis occasionally found. COASTALCLIFF COMMUNITIES: The steep slopes of Chatham Bay are representative of the cliff vegetation around the island. The open overstory is primarily the endemic Cecropia pittieri (Cecropiaceae) mixed with Clusia rosea. The overwhelming majority of the vegetation is a mixture of Ipomoeaspp. vines forming a nearly vertical green wall. The sedge, Rhynchospora polyphylla, stinging nettle, Laportea aestuans, and red-flowered Kohleria spicata are some of the few herbaceous plants that are common on the cliffs near the shoreline. In less steep areas, the closed-canopy forest vegetation reaches to the shore. Here it is possible to find a canopy of the endemic tree Sacoglottis holdridgei (Humiriaceae) along with tree species Ocotea insularis and Clusia rosea. The understory is composed of melastome shrubs such as Ossaea macrophyllaand O. bracteata. A unique feature of this vegetation is the presence of the endemic tree fern Cyathea nesiotica TRUSTYETAL.: VASCULAR FLORAOF ISLADELCOCO, COSTARICA 251 (Cyatheaceae) which is restricted to these moderately steep areas that receive more sunlight. Many waterfalls cascade from these cliffs into the sea. RIPARIANAREAS: The unusually high rainfall and steep terrain of Isla del Coco support many streams and rivers. The largest and most permanent of these rivers are those leading into the three bays at Chatham, Wafer and Iglesias. The overstory of the riparian areas is the same as the rest of the island with an abundance of Sacoglottis holdridgei, Ocotea insularis, and Clusia rosea trees. The sedge, Calyptrocarya glomerulata, the aroid Spathiphyllum laeve, and the fernDanaea nodosa are abundant along river and stream banks throughout the island. At the lower elevations (0–50 m) of Wafer Bay, the Genio River and its tributary streams are home to Rustia occidentalisand Pilea gomeziana.The endemic Hoffmannia piratarum(Rubiaceae) is restricted to the Genio River riparian area. The Iglesias River on the southwestern side of the island is only accessible for a short section from the waterfall to the sea. This area is home to a small grove of the endemic tree Eugenia cocosensis(Myrtaceae) and an understory including the shrub Psychotria gracilenta. The Chatham River leading to Chatham Bay is much steeper and has large boulder outcrops along the edges. The endemic shrub Ardisia cuspidata(Myrsinaceae) is common along the banks of this river. LOWELEVATIONHUMIDFOREST. The majority of the island is classified as premontane rain forest in the Holdridge life zone system (Holdridge 1974). Tree diversity is extremely low. Only five species of canopy trees were recorded in a study of all tree species over 10 cm diameter at breast height (dbh) in ten 400 m2 plots along an east-west elevational transect from 30 m to the highest elevation at 630 msl on the north-eastern slope of Cerro Iglesias. These are Sacoglottis holdridgei, Clusia rosea, Ocotea insularis, Henriettella fascicularis and Miconia dodecandra. Ficus pertusa, Eugenia cocosensis, and Brosimum sp. are also found sporadically along the north side of the island. The shrub layer in this vegetation zone is dense and diverse with many melastomes and two common endemic tree fern species, Cyathea alfonsiana and C. notabilis. The sole forest palm is Euterpe precatoriavar. longevaginata. The herbaceous layer consists mostly of fern species and the large sedge species Hypolytrum amplum. Thick lianas of Schlegeliabrachyanthaand Entada gigas wind through the trees. A notable aspect of this forest is the density and diversity of epiphytic species. The forest appears a mixture of green and red from the abundance of the bromeliad Guzmania sanguinea that covers nearly every tree. In addition, four orchid species are commonly found including the endemics Epidendrum cocoënse and E. insulanum. There are many epiphytic ferns and two endemic pendent epiphytes, Huperzia brachiataand H. pittieri. HIGHELEVATIONCLOUDFOREST: The cloud forest on Cocos Island begins around 450 m elevation and is restricted to the two highest peaks on the island, Cerro Iglesias and Cerro Pelon. The canopy of this forest is exclusively Sacoglottis holdridgei with an understory largely dominated by the tree fern Cyathea alfonsiana.These large trees and tree ferns are completely covered in a thick layer of mosses and the whole forest constantly drips as the clouds roll over the peak. Freziera calo- phylla, Hedyosmum racemosumand the endemic fern Elaphoglossum reptansare known on Isla del Coco only from these cloud forests. LANDSLIDES: Due to the abundance of rain and its rugged terrain, Cocos Island has many landslides both near the coast and inland (Fournier 1966). These open areas are quickly covered with the vining ferns Dicranopteris flexuosa, D. pectinata and Sticherus remotus and vines of several species of Ipomoea. These species are joined by Cecropia pittieri. These successional areas caused by landslides are common and probably constant features of the Cocos Island vegetation. ISLETS: There are more than ten small islets surrounding Isla del Coco and three of them (Isla Manuelita, Isla Ulloa and Isla Muela) were visited during our research. These small islets do not contain much soil as a result of constant weathering by the wind and sea. Only two species of plants, 252 PROCEEDINGS OF THE CALIFORNIAACADEMYOF SCIENCES Fourth Series, Volume 57, No. 7 Clusia rosea and the endemic grass Chloris paniculata were recorded on these islets. The overwhelming majority of the plants of Chloris paniculata are found on these small islets although a few small sub-populations are found on the coastal cliffs of Isla del Coco near the islets. Human Impacts The biota of oceanic islands is unique and fragile. The paucity of species in island habitats increases the importance of the native species in ecosystem function and dynamics. The biological equilibrium of oceanic islands is very sensitive to any external alteration. The impact of humans and their introduced animals and plants on the biota of oceanic islands is well known (Moulton and Pimm 1986; Quammen 1996; Haberle 2003). There have been many examples of extinctions pro- duced by the intentional or accidental intervention of man in fragile ecosystems such as islands. Isla del Coco is not excluded from this list. In the nearly 500 years since the island was discovered, man has impacted its ecosystems. HUMANINHABITANTS: Isla del Coco has not had extensive human inhabitation. The island func- tioned as a prison colony between 1874 and 1877 in Chatham Bay (Alfaro 1898). The longest tenure any human has had living on the island was by August Gissler and his wife who spent 16 years from 1889 to 1905 in Wafer Bay. Gissler brought 13 German families to work in the Cocos Island Agricultural Company (Jinesta 1937), but very few families stayed for a second year. Today, the park has two stations, one in Chatham Bay that houses four people and the other in Wafer Bay that houses up to 30 people. The majority of the island has remained uninhabited. Recently, there has been a hydroelectric facility installed on the Genio River in Wafer Bay that provides power to the ranger station. INTRODUCED ANIMALS: In July of 1793 James Colnett, captain of the English whaler Rather, introduced pigs and goats onto the island (Lievre 1893). Today, the feral pig (Sus scrofa) is abundant and is one of the main threats for the native plants of Cocos Island. Although this introduction has had the greatest negative environmental impact on the island, it is not the only animal introduction. Paca (Agouti paca), white-faced monkeys (Cebus capucinus), domestic dogs (Canis famil- iaris), domestic rabbits (Oryclolagus cuniculus) and guinea hens (Numida meleagris) have all been introduced (Madrigal 1954; Rojas 1964). However, none of these introduced vertebrates have pros- pered, and they do not occur on the island today. The current introduced fauna of the island consists of feral pigs, feral cats (Felis domesticus), goats (Capra hircus), white-tailed deer (Odocoileus virginianus) and two species of rats (Rattus rattusand Rattus norvegicus) (Montoya 1990; Gómez 2004). An estimated 400–500 feral pigs occur on Isla del Coco (Sierra 2001a). Research has shown that areas rooted by the feral pig population have a rate of soil erosion nearly 100 times greater than unrooted areas and that 10–20% of the total island surface is rooted annually by these animals (Sierra 2001b). Rooting is a major soil disturbance and can increases the loss of soil nutrients (Singer et al 1984). Rooting diminishes the abundance of soil arthropods (Vtorov 1993) and reduces and/or modifies the structure of the herbaceous vegetation (Bratton 1974; Diong 1982). In addition, Sierra (2001a) found that 88% of the stomach contents of the feral pigs is vegetable matter, with 63% fruits ofMoraceaespp., Annona glabra, and Ocotea insularis. Sierra (2001a) did not find that the pigs were dispersing the seeds of any exotic species. Park officials have approved the eradica- tion of feral pigs (Montoya 1990) but are awaiting funding. Studies of the rat populations of Isla del Coco have added to our knowledge of their impacts on the island. Gómez (2004) found that rat densities on the island range from 45 rats/ha in the cloud forest of the island to a high of 156 rats/ha near the inhabited area of Wafer Bay. Rats are also found on many of the islets near the island. Gómez (2004) also found that 70% of the stomach contents TRUSTYETAL.: VASCULAR FLORAOF ISLADELCOCO, COSTARICA 253 of these animals is vegetable matter. In addition, he found that 68% of seeds of the endemic tree Sacoglottis holdridgeiwere gnawed on by rats (Gómez (2004). INTRODUCED PLANTS: The first account of exotic plant species on Isla del Coco was by Don Francisco Bernardo de Quiroz in 1546 who wrote, “ I planted some plants and fruits brought from Peru” (Sierra 1998). This early account was only 20 years after the discovery of the island. Passmore (1895) recorded pumpkins and grapes on the island, while Pittier (1898) recorded jocote (Spondias lutea), achiote (Bixa orellana), and marañones (Anacardium occidentale). August Gissler (1889–1905) and his Cocos Island Agricultural Company cultivated a large area in Wafer Bay with bananas, beans, cacao, coffee, corn, avocado, achiote, sugar cane, oranges, limes, pineapples, tobac- co, cherimola, almonds and yuca (Jinesta 1937). Today, avocado, bananas, cacao and coffee remain from Gissler’s fields. In addition, the park service personnel maintain several tropical fruits and vegetables in cultivation for their own consumption. The only cultivated plant that has managed to escape into at least two known forested areas of the island is the shade-loving coffee plant. It is uncertain to what extent the species with extensive, worldwide or pantropical distributions have reached the island because of human intervention. Drift disseminated species such as Cocos nucifera, Mucuna sloanei, and Ipomoea pes-caprae have seeds that can survive and germinate after long periods floating at sea (Guppy 1906). The propagules of weedy species such as Rolandra fru- ticosa,Urena lobataand Drymaria cordata are small and can be moved by wind or can be easily dispersed by migrating birds (Ridley 1930; Carlquist 1970). In contrast, a number of plant species are commonly associated with humans. Species such as Sida acuta, Phyllanthus urinaria, Hydrocotyle umbellata and many grass and sedge species are usually found only in human dis- turbed areas or around dwellings. It is likely that these species were accidentally introduced by humans. Unfortunately, due to the lack of early plant collections, knowing whether a plant is native but widely distributed or whether it has been accidentally introduced is a difficult distinction to make. For this publication, any ruderal species first found after 1905 is considered accidentally introduced by humans unless there is evidence to the contrary. This date was chosen because it is the date of the first fairly complete plant collection for the island published by Stewart (1912). By these criteria, we consider 71 species to have been intentionally or accidentally introduced to Isla del Coco by humans in the last 100 years. DEFORESTATION: The most apparent impact man has made on the vegetation of Isla del Coco is through deforestation. Many mariners cut wood or collected coconuts from the islands throughout its history. Lievre (1893) stated that many coconuts were collected by felling the coconut palms. This activity led to the 1895 account that there were no coconut palms on Isla del Coco (McCartney 1895). Despite this extensive harvesting, coconuts can still be found in isolated coastal locations. The deforested areas of Isla del Coco are limited to the areas near Chatham and Wafer Bays. The area near Chatham Bay was deforested for agriculture in 1874 by the penal colony and despite the cessation of agriculture for the past 125 years, remains deforested to this day (Alfaro 1898; Sierra 1998). Previous Botanical Research Although the island had been known to mariners since the sixteenth century (Hertlein 1963) the first known plant collections from Isla del Coco were made in 1838 by George W. Barclay during the voyage of H.M.S. Sulfur(Belcher 1843). Fifty years after these initial collections, Alexander Agassiz of Harvard University collected a number of plants in 1888 and 1891 during expeditions of the United States Fish Commission (Agassiz 1891–1892). Agassiz, like many of the subsequent plant collectors, spent a few days on Isla del Coco as a stop during his trip to the Galápagos Islands. Six years after Agassiz’expedition, the Costa Rican government funded Anastasio Alfaro, Henri 254 PROCEEDINGS OF THE CALIFORNIAACADEMYOF SCIENCES Fourth Series, Volume 57, No. 7 Pittier and Paul Biolley to visit in 1898 and 1902 in the interest of re-instating the use of the island as a penal colony (Pittier 1898). The three naturalists suggested that the island should be conserved as a protected area instead. Pittier’s plant collections are the basis of nine species endemic to Cocos Island (Pittier 1898). Robert E. Snodgrass and Edmund Heller, naturalists aboard the Hopkins- Stanford Expedition in 1899, also collected on Cocos Island (Robinson 1902). One of the most complete early botanical expeditions to Cocos Island was accomplished by Alban Stewart who collected in 1905 for the California Academy of Sciences (Stewart 1912). Interest in plant collecting on Isla del Coco was renewed in the 1930s with the Vincent Astor expedition of 1930 with botanist Henry K. Svenson (Svenson 1935, 1938) and during the Templeton-Crocker Expedition sponsored by the California Academy of Sciences in 1932 with the plant collections of John T. Howell. The Presidential Cruise of the United States stopped on Cocos Island in 1935, 1937 and 1940 and collections were made and sent to the United States National Herbarium. In 1964, W.L. Klawe collected Isla del Coco plants as part of the Galápagos Islands International Scientific Project (Fournier 1966; Fosberg and Klawe 1966). Plant collecting on Cocos Island has greatly increased in the last decades due to the establishment of Isla del Coco National Park and the availability of transportation to the island. The majority of this work has been conducted by Costa Rican botanists from the Universidad de Costa Rica, Universidad Nacional de Costa Rica and the Instituto Nacional de Biodiversidad. Collectors include Gregorio Dauphin, Robin Foster, Luis Diego Gómez, Jorge Gómez-Laurito, Jose González, Leslie R. Holdridge, Alfonso Jiménez, Eduardo Lépiz, Luís Poveda, Francisco Quesada, Alexander Rojas, Pablo Sánchez, Ricardo Soto, and Manuel Valerio. Table 1 (See Appendix) gives a summary of the most important historical botanical collections from Isla del Coco with details on the dates, institu- tions/countries which organized these expeditions, and the locations of the specimens collected. Despite the number of collectors who have visited the island, there are relatively few published works on the plants of Isla del Coco and no complete flora has been assembled. The earliest published records of vascular plants for Isla del Coco are those of Bentham (1844–1846), Rose (1892), Pittier (1898), Robinson (1902), Stewart (1912) and Svenson (1935, 1938). It was not until 1966 when Fosberg and Klawe published the “Preliminary List of Plants from Cocos Island” that this information was assembled for the island (Fosberg and Klawe 1966). Many new collections have been made since this checklist was published and better taxonomic and floristic treatments have aided in the identification of previous collections and in the description of new species (e.g., Gómez 1971; Burger 1975; Gómez 1975; Gómez 1976; Hamilton 1988; Rojas-Alvarado 2003; Rojas- Alvarado and Trusty 2004). The present work, synthesizes over 150 years of collection data along with data from recent expeditions, stands as the first complete flora for this island. BOTANICALWORKTHATMAKESUPTHISVOLUME: We have compiled a list of all the species previously collected or currently present on Isla del Coco and have updated the taxonomy and nomen- clature for these species. This research is based both on the study of herbarium specimens and also on material collected by us during our recent expeditions to Cocos Island. Three collecting trips were made between 2001 and 2002: Trusty (July 2001), Trusty and Kesler (January–March 2002) and Trusty and Kesler (November–December 2002). Atotal of 497 numbers was collected during these three trips. Complete sets of these collections can be found in the Museo Nacional de Costa Rica (CR) and Fairchild Tropical Botanic Garden (FTG); partial sets are located in the California Academy of Sciences (CAS), the Instituto Nacional de Biodiversidad (INB), and Universidad de Costa Rica (USJ). In addition, the original plant collections of all published species were reviewed in CR, USJ, INB, the Gray Herbarium at Harvard (GH), and the Smithsonian Institution (US). Loans were obtained of collections from Isla del Coco housed at the California Academy of Sciences (CAS), the Brooklyn Botanic Garden (BKL) and US. More than 1800 specimens were TRUSTYETAL.: VASCULAR FLORAOF ISLADELCOCO, COSTARICA 255 studied including historical and type collections. These collections were verified and annotated. On the basis of these specimens and current taxonomic treatments, we recognize 263 species on Isla del Coco. Fifty-one species are new records for the island. Twenty-eight of these were collected by J. Trusty. Eleven previously published species are either excluded from the flora or are considered as doubtful occurrences. In addition, information about species’abundance and distribution on the island is provided. The abundance designations are: rare, infrequent, frequent, locally common, common and very common. These are subjective assessments made by the authors based on the fre- quency of encounter from least to greatest. The List of Exiccatae provides a summary of the herbarium specimens that are the basis for this flora. PLANT BIOGEOGRAPHY The known native vascular flora of Isla del Coco now stands at 263 species. One of these is identified only to genus (Brosimum sp.) due to lack of adequate material. Of the 262 identified species, 37 are endemic to the island and 154 are considered native. Seventy-one species are considered introduced by humans. Asummary is given in Appendix Table 2. ENDEMICSPECIES:Isla del Coco is home to 33 endemic plant species and four endemic varieties representing 24% of the native flora. This rate is relatively low when compared to other islands or archipelagos in the Pacific. The nearby Galápagos Island flora boasts an endemism rate of 43%, the Juan Fernandez Islands have 60%, while Hawaii boasts 97% (Wagner et al. 1990; Lavergne et al. 1999, Baeza et al 2002). Single islands such as Rodriques, La Réunion and Mauritius have endemism ranges between 29–45% (Lavergne et al. 1999). The small size and young age of Isla del Coco may influence the low rate of endemism on this island. Six genera on Isla del Coco have more than one endemic species on the island (Cyathea, 3 spp.; Elaphoglossum, 3 spp.; Epidendrum, 3 spp.; Eugenia, 2 spp.; Hoffmannia, 2 spp. and Miconia, 2 spp.). Preliminary molecular evidence for Epidendrum and Miconia(J. Trusty et al., in prep.) and morphological assessments for Cyathea do not suggest the endemic species to be sister taxa (M. Turner, pers. commun.). This evidence suggests that although a moderate number of new species has evolved on the island, a radiation event has not occurred. Most endemic species on Isla del Coco are the result of separate introductions from the mainland. The endemic flora of Isla del Coco is unique in that 50% of the endemics are fern species. In no other island flora does the number of fern endemic species equal that of flowering plant endemics (Smith 1972; Given 1993). In addition, the total fern diversity is high, with 80 species making up 30% of the total flora of Isla del Coco. In comparison, ferns in continental areas repre- sent a much smaller proportion of the flora. For example, ferns constitute only 9% of the vascular plant diversity of Costa Rica (Moran 1993). ORIGINOFTHEFLORA:The majority of the species on Isla del Coco are considered to be Central or South American in origin due to the proximity of the island (500 km) to mainland Costa Rica. The distributional ranges of the native species are listed in the Species Descriptions and a summary is given in Appendix Table 3. The floristic affinities of the endemic species based on the distribution of putative sister species are compiled in Appendix Table 4. The close relationship of the Isla del Coco flora with the Caribbean Islands and Central America is shown with 66.8% of all Cocos Island native taxa present on at least one island in the Caribbean and 95.7% present in Central America. This biogeographic relationship was suggested by Croizat (1958) who considered Isla del Coco to be a part of a biogeographical track that joins the Caribbean, Central America and the Galápagos Islands. This biogeographical track has been confirmed by the geological and tectonic history of the region (Rosen 1976; Haug and Tiedemann 1998). To date, no floristic links have been 256 PROCEEDINGS OF THE CALIFORNIAACADEMYOF SCIENCES Fourth Series, Volume 57, No. 7 found between Isla del Coco and the Galápagos Islands and they only have 26 plant species in common (Trusty et al., in prep.). Approximately 30% of plants native to Cocos Island are pantropical in distribution. Using the guidelines proposed by Carlquist (1974), the most likely dispersal mode was determined for each species found on Isla del Coco based on seed size, palatability for birds, presence/absence of appendages or glands, ability to float and/or published dispersal mode (Carlquist 1974; Croat 1978; STRI 2004; NYBG 2004; data available from J. Trusty on request). The results of this analysis are shown in Appendix Table 5. Approximately 47.1% of native species are considered dispersed by wind, 11.5% by water, 26.7% internally by birds and 14.7% external- ly by birds. WIND PATTERNS: The climate of Isla del Coco is determined by the northern and southern migration of the Inter-Tropical Convergence Zone (ITCZ). The ITCZ is an air current that moves from 2–4° North latitude between February and April to 11–15° North latitude between August and September. During most of the year there is an eastward flowing equatorial counter current bringing clouds, rain and a persistent southeast wind. In contrast, when the ITCZ is closest to Isla del Coco in February or March, the equatorial current becomes a westward current bringing drier air (Montoya 1990). The majority of wind-dispersed plants is fern or orchid species due to their minute spores and seeds. Ferns and orchids are predisposed to the colonization of insular environments due to their incredible dispersal abilities. Fern spores are microscopic with nearly 80% of pteridophyte species within a range of 20 to 60 micra in diameter (Tryon 1970). The small size of fern spores allows them to be easily transported by air currents, and it has been said that distances of 800 km is not a significant barrier (Tryon 1970). Orchid seeds are often described as “dust-like” and range in size from 150 to 6000 micra in diameter (Molvray and Kores 1995). The seeds also have large internal air spaces that allow them to float on air for long periods of time, facilitating long distance transport (Arditti and Ghani 2000). In addition to the ease of transport, fern spores and orchid seeds are particularly numerous; a single plant can produce thousands of propagules at one time and many millions in a lifetime (Carlquist 1965; Arditti and Ghani 2000). Once the propagules have arrived, the wet, tropical environment on Isla del Coco is beneficial to the establishment and survival of fern and orchid species. Although air currents flow westward from the mainland of Central America/northern South America for only a small part of the year, many fern and orchid species have successfully made the voyage to Isla del Coco as evidenced by the high proportion of these plants in the total flora. Due to the remarkable dispersal ability of ferns and orchids, it is surprising that these air dispersed groups make up the majority (56.8%) of endemic species on Isla del Coco. If large numbers of orchid seeds and fern spores were continuously colonizing the island, the genetic input of these mainland populations would prevent the Isla del Coco populations from diverging into new species via genetic drift or selection. Unless the island populations had developed a method of reproduc- tive isolation via mutation or chromosome rearrangement, the influx of mainland genes would reunite the island population with the mainland species and likely swamp out the traits under selection in the island environment (Templeton 1982, Futuyma 1998). The presence of 18 endemic fern taxa and three endemic orchid species indicates that although ferns and orchid propagules are able to survive the long journey to Isla del Coco, this event is rare for many species. OCEAN CURRENTS: Isla del Coco is situated in the eastern Pacific where a complex series of marine currents join. The system of ocean currents that influences the island is made up of three main components: strong eastern circulating currents that transport warm tropical water along (and slightly north) of the equator two western circulating cold currents that parallel the warm equatori-