There are four universally recognized vegetation zones, which occur throughout the archipelago: Littoral, Dry, Transition, and Humid.
Littoral Zone
This is the coastal fringe of the islands and includes beaches, mangroves and brackish lagoons. Predominant plants are the mangrove trees, and in drier areas bushes and grasses that tolerate salt. The four mangrove tree species that are commonly found in protected coves and lagoons are red (Rhizophora mangle), black (Avicennia germinans), white (Laguncularia racemosa), and button mangrove (Conocarpus erecta). Some of the smallest islets are entirely covered by Littoral Zone vegetation.
Dry Zone
The Dry Zone is the most widely distributed zone, and many islands, even some of the larger ones such as Genovesa, have no other vegetation type except the coastal fringe. The Dry Zone rises higher on the north side of the higher islands, which is in the rain shadow of their peaks. It can often be subdivided into a lower scrub zone and an upper woodland zone. This region is home to many cacti such as prickly pear (Opuntia spp.), giant candelabra cactus (Jasminocereus thouarsii) and the pioneer that settles into hardened lava flows, the lava cactus (Brachycereus nesioticus).
Transition Zone
Vegetation becomes denser as the altitude and rainfall increase. The Transition Zone includes species from both the lower Dry and the upper Humid Zones. There is a variety of small trees or shrubs, including the endemic Guayabillo, with a small white flower, and a small guava-like fruit, and the endemic Galapagos tomato that is salt tolerant.
Humid Zone
Depending on the local rainfall, altitude and soil type, this zone may be further divided into sub-zones: the Scalesia forest (a zone dominated by a tree daisy), Miconia scrub and the Pampa zone (dominated by ferns and sedges at the highest altitudes). The humidity is highest in the humid zone, although much of the moisture comes from misty conditions rather than rain, and the vegetation is rich in bromeliads, ferns, orchids and mosses, many of them growing as epiphytes on tree branches.
Only the seven highest islands, such as Santa Cruz and Isabela, include all these zones.