warmest and wettest month, with temperatures as high as 30°C and as much as 80 mm of rainfall. Temperature and rainfall vary with elevation, creating a range of microclimates on the higher islands. Average annual temperature declines an average of 0.9°C for every 100 meters of elevation, and rainfall increases. Average annual rainfall for the archipelago is 356 mm at sea level and 1092 mm at 200 meters elevation. Flora Most of the Galápagos is covered in semi-desert vegetation, including shrublands, grasslands, and dry forest. A few of the islands have high-elevation areas with cooler temperatures and higher rainfall, which are home to humid-climate forests and shrublands, and montane grasslands, or pampas, at the highest elevations. There are about 500 species of native vascular plants on the islands, including 90 species of ferns. About 180 vascular plant species are endemic. Coastal plant communities are generally low-growing shrubs and herbs which are tolerant of drought and salt spray. Typical plants include the shrubs saltbush (Cryptocarpus pyriformis) and Maytenus octagona. Herbaceous seashore plants include the widespread beach morning glory (Ipomoea pes-caprae) and Sesuvium portulacastrum, and the endemic Galápagos carpet weed (Sesuvium edmonstonei). Mangroves grow in calm inlets and lagoons. Typical species include red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans), and white mangrove (Laguncularia racemosa) and button mangrove (Conocarpus erectus). The arid zone lies inland of the coastal zone and extends to 200 meters elevation or higher. It covers most of the archipelago. It includes trees, shrubs, cacti, and herbs adapted to dry conditions. Common trees include the palo santo (Bursera graveolens) and paga paga (Pisonia floribunda), and the endemic trees guayabillo (Psidium galapageium) and Bursera malacophylla, which is found only on Seymour, Baltra and Daphne islands. Cacti include several endemic species of Opuntia – Opuntia echios, O. helleri, and others – and the endemic genera Jasminocereus and Brachycereus. Ground cover plants include low shrubs, like the endemic bitterbush (Castela galapageia) and species of the endemic genus Lecocarpus, and herbaceous plants. Herbaceous arid zone species include the endemic genera Tiquilia and Chamaesyce, Galápagos tomato (Solanum galapagense), and stinking passion flower (Passiflora foetida). On islands that reach higher elevations, there is transition zone between the arid and humid zones between 200 and 300 meters elevation. Transition zone plants include Pisonis floribunda and Psidium galapageium at lower elevations, and P. galapageium with Scalesia trees closer to the humid zone. The humid zone lies above