Plant Formations in the Chocóan BioProvince Peter Martin Rhind Chocóan Upland Rain Forest (Bajo Calima) These forests occur on low hills composed of Tertiary sediments. The soils are very low in nutrients and possibly have the lowest phosphorus levels of any known Neotropical forest. At canopy level the palm Jessenia batava appears to be the most common species, but other palms such as Socratea exorrhiza and species of Wettinia are also common and, in fact, these forests appear to support more palm species than any other part of the World. Other dominant canopy trees include Eschweilera panamensis (Lecythidaceae), Manilkara bidentata (Sapotaceae) and Otoba lehmannii (Myristicaceae), while other important trees are Brosimum utile (Moraceae), Miconia punctata (Melastomataceae), Micropholis crotonoides (Sapotaceae), Pouteria buenaventurensis (Sapotaceae), Tovomita weddelliana (Clusiaceae), Welfia georgii (Arecaceae) and Wettinia quinaria (Arecaceae). However, the overstory or canopy of these forests is extremely rich with up to 258 species recorded in just one hectare. Important families in terms of species-richness include Annonaceae, Arecaceae, Hypericaceae, Fabaceae, Melastromataceae, Rubiaceae and Sapotaceae. These forests are also especially important for the family Burseraceae in terms of species-richness, endemism and ecological dominance, and for the prevalence of Bombacaceae especially the genus Quararibea. In fact, trans-Andean forests appear to be the centre of diversity for this genus. The under storey is variable but typically includes Mabea occidentalis (Euphorbiaceae), Macrolobium archerii (Fabaceae), Miconia centronoides (Melastomataceae), Pausandra trianae (Euphorbiaceae), and Tetrorchidium ochroleucum (Euphorbiaceae), and can, in fact, support up to three times as many trees as the over storey. The most important shrub families are Melostomataceae, Piperaceae, Rubiaceae and Solanaceae. There is a very high diversity of climbers although most of these are hemi epiphytes, including species of Cavandisha, Clusia, Drymonia, Ficus, Marcgravia, Norantea, Schradera and Topobea, rather than free- climbing lianas. Normal epiphytes are also well represented particularly by the Araceae, but also include many bromeliads, cycanths, gesneriads, orchids, and peperomias. Among the terrestrial herbs Acanthaceae, Commelinaceae and Gesneriaceae are well represented. Chocóan Coastal Wet Forest On the basaltic rocks of Cape Corrientes, Colombia where there is a short dry season between January and March, the closed canopy wet forest reaches heights of up to 45 m and has emergents extending up to 59 m. The emergent species include Brosimum utile (Moraceae), Caryocar amygdaliferum (Caryocaraceae) and Ceiba aff. pentandra (Malvaceae), with many of these tall trees having large buttress roots. The most abundant canopy species are Otoba latialata and Otoba novogranatensis (Myristicaceae), Oenocarpus bataua (Arecaceae), Welfia regia (Arecaceae) and Wettinia quinaria (Arecaceae). Here the most abundant families are Arecaceae, Clusiaceae, Fabaceae, Moraceae, Myristicaceae and Sapotaceae. The largely open under storey is mainly composed of smaller versions of the species mentioned above but also includes Conostegia setosa (Melastomataceae). Arecaceae is the most abundant family followed by Fabaceae, Melastomaceae, Moraceae and Myristicaceae. In terms of species-riches, 124 tree species with basil diameters greater than 10 cm were recorded in a one-hectare plot and these comprised 86 genera and 40 families. This forest like other Chocó forests was found to be notable for its abundance of arboreal palms and possibly has a higher number of palm species than any other Neotropical forest. Also in line with other Chocó forests the hemi epiphytes are more prevalent than lianas. Chocóan (Tumbesian) Acacia Thorn-Forest Thorn-forest characterized by Acacia species such as A. macracantha and A. tortuosa can replace other natural forests when they have been heavily degraded, but they are also thought to occur naturally on the lower slopes of the Tumbesian zone. These normally form open stands between 5-10 m tall and are largely deciduous. Common trees include Bursera graveolens (Burseraceae), Caesalpinia corymbosa (Fabaceae), Capparis mollis (Capparaceae), Muntingia calabura (Muntingiaceae), and where there is some groundwater influence Celtis iguanea (Cannabaceae) and Zizyphus piurensis (Rhamnaceae). Typical shrubs are Capparis cordata (Capparaceae), Cercidium praecox (Fabaceae), Cereus macrostilbas (Cactaceae), Cryptocarpus pyriformis (Nyctaginaceae), Encelia canescens (Asteraceae), Galvezia limensis (Plantaginaceae), Grabowskia boerhaviifolia (Solanaceae), Isocarpus microcephala (family?), Maytenus orbicularis (Celastraceae), Mimosa acantholoba (Fabaceae), Parkinisonia aculeata (Fabaceae) and Vallesia dichotoma (Apocynaceae). The deciduous herb layer develops into a dense, lush and fairly high structure during the rainy season. The main species include grasses and forbs such as Anthephora hermaphrodita (Poaceae), Aristida adscensionensis (Poaceae), Bouteloua disticha (Poaceae), Chloris virgata (Poaceae), Heliotropium angiospermus (Boraginaceae), Luffa operculata (Cucurbitaceae), Nicandra physaloides (Solanaceae), Schizoptera trichotoma (Asteraceae) and Sicyos chaetocephalus (Cucurbitaceae). Chocóan (Tumbesian) Ceiba trichistandra Forest This largely lowland forest ranges from mainly deciduous to semi-evergreen. The bulbous character of the evergreen, dominant Ceiba trichistandra (Malvaceae) make these forests very distinctive and in the more deciduous stands spiny red-barked Erythrina velutina (Fabaceae) adds to the distinctiveness. Undisturbed forest usually has a closed canopy that can reach heights of 25 m but with certain trees reaching 35 m. The other main canopy trees in the mainly deciduous forests of Tambo Negro include Cochlospermum vitifolium (Bixaceae), Eriotheca ruizii (Malvaceae), Erythrina velutina (Fabaceae), Hura crepitans (Euphorbiaceae) and Tabebuia chrysantha (Bignoniaceae). A sub canopy of small trees and shrubs includes Achatocarpus nigricans (Achatocarpaceae), Albizia multiflora (Fabaceae), Armatocereus cartwrightianus (Cactaceae), Capparis heterophylla (Capparaceae), Carica parviflora (Caricaceae), Croton fraseri (Euphorbiaceae), Ficus americana (Moraceae), Guazuma ulmifolia (Sterculiaceae), Phyllanthus anisolobus (Phyllanthaceae), Pithecellobium excelsum (Fabaceae), Rauvolfia tetraphylla (Apocynaceae), Senna atomaria (Fabaceae), Trichilia hirta (Meliaceae), Triplaris cumingiana (Polygonaceae) and Urera baccifera (Urticaceae). The herb layer is draught deciduous and only conspicuous during the rainy season but contains few grasses. Annuals and geophytes like Adiantum raddianum, Brachiaria fasciculata, Coursetia caribaea and Talinum paniculatum represent much of the ground cover. The few grasses may include Andropogon bicornis, Aristida adscensionensis, Chloris virgata and Pennisetum occidentale. Cacti, orchids, and bromeliads like Guzmania monostachya, Pitcairnia prolifera, Vriesea espinosae and various species of Tillandra, dominate the epiphytes. Other epiphytes include Rhipsalis micrantha and Trichocentrum tigrinum, but overall the epiphytic flora although abundant is not particularly rich in species. Climbers are conspicuous and seem to include a high proportion of cucurbit taxa such as Apodanthera, Momordica and Sicyos. Chocóan (Tumbesian) Low Montane Cloud Forest Situated on the lower seaward slopes at altitudes ranging from 500-1500 m these forests are constantly subject to very humid conditions because of condensation from frequent cloud cover and is little affected by the dry season. In the Buenaventura area these often open canopy forests can reach heights of 35 m and have emergents extending up to 45 m. Depending on location some of the characteristic tree species include Centrolobium paraense, Podandrogyne brevipedunculata, Matisia cordata, Ochroma pyramidale, Mabea occidentalis, Muntingia calabra, Rheedia edulis, Symphonia globulifera, Spondias purpurea, Tabebuia guayacan, Vemonia baccharoides, Banara guianensis, Conostegia cuatrecasii, Ossaea boeckii, Cedrela odorata, Ficus gigantorice, Myrica pubescens, Bocconia integrifolia, Coccoloba obovata, Oreocalyx grandiflora, Turpinia occidentalis, Heliocarpus americanus, Urera caracasana and various species of Miconia. The open conditions allow sufficient sub canopy light for dense middle and under storey formations, and as expected the epiphytic flora is well developed. In fact, dense mats of epiphytes cover much of the canopy branches. These include numerous lichens, bryophytes, ferns, orchids, and species of Araceae and bromeliads. The latter include a large number of Guzmania species such as G. angustifolia, G. garciaensis and G. hitchcockiana which here are much more prevalent than Tillandsia species which tend to be more numerous in less humid conditions. The few species included T. acosta-solisii, T. narthecioides, T. pseudotetrantha and T. venusta. Chocóan (Darien) Tropical Moist Forest These forests are notable for the size, number and height of the trees. The canopy can reach heights of 40 m and further characterized by the giant emergents like Cavanillesia platanifolia and Ceiba pentandra. Both of these are deciduous and their naked branches can be a striking feature from the air. Other important canopy trees include Anacardium excelsum, Bombacopsis sessilis, Enterolobium cyclocarpum, Licania hypoleuca, Platypodium elegans, Pseudobombax septenatum, Sterculia