The Hawaiian tropical rainforests are a tropical moist broadleaf forest ecoregion in the Hawaiian Islands. They cover an area of 6700 km2 in the windward lowlands and montane regions of the islands. Coastal mesic forests are found at elevations from sea level to 300 m. Mixed mesic forests occur at elevations of 750 to 1250 m, while wet forests are found from 1250 to 1700 m. Moist bogs and shrublands exist on montane plateaus and depressions. For the 28 million years of existence of the Hawaiian Islands, they have been isolated from the rest of the world by vast stretches of the Pacific Ocean, and this isolation has resulted in the evolution of an incredible diversity of endemic species, including fungi, mosses, snails, birds, and other wildlife. In the lush, moist forests high in the mountains, trees are draped with vines, orchids, ferns, and mosses. This ecoregion includes one of the world's wettest places, the slopes of Mount Waialeale, which average 373 in of rainfall per year.

Coastal mesic forests

Coastal mesic forests are found on the windward slopes of the major islands from sea level to 300 m. These forests have been dominated by the native hala (Pandanus tectorius) and hau (Hibiscus tiliaceus) and naturalized (Polynesian introductions) kukui (Aleurites moluccana) and milo (Thespesia populnea) for the past 1,000–2,000 years. The Polynesian-introduced noni (Morinda citrifolia), pia (Tacca leontopetaloides), and kī (Cordyline fruticosa) are also common in this zone. Other native species include pololei (Ophioglossum concinnum), ākia (Wikstroemia spp.), loulu fan palms (Pritchardia spp.), ōhia lehua (Metrosideros polymorpha), and lama (Diospyros sandwicensis).

Mixed mesic forests

Mixed mesic forests, at 750 to 1250 m on the windward slopes of the large islands in addition to the summit of Mount Lānaihale on Lānai, receive 1000 to 2500 mm of rainfall annually and thus may not be true rainforests. The forest canopy, dominated by koa (Acacia koa) and ōhia lehua (Metrosideros polymorpha), is somewhat open, but tree density is rather high. Other trees and shrubs include pāpala (Charpentiera obovata), olopua (Nestegis sandwicensis), hame (Antidesma platyphyllum), mēhame (A. pulvinatum), kōpiko (Psychotria mariniana), ōpiko (P. mauiensis), iliahi (Santalum freycinetianum), hōlei (Ochrosia spp.), poolā (Claoxylon sandwicense), kōlea lau nui (Myrsine lessertiana), kauila (Alphitonia ponderosa), nioi (Eugenia reinwardtiana), aiai (Paratrophis pendulina), and hōawa (Pittosporum spp.).

Wet forests

Wet forests generally occur from 1250 to 1700 m, but may be as low as 200 m. They receive 3000 to 11250 mm of rain per year. Ōhia lehua (Metrosideros polymorpha) is the dominant canopy species in wet forests, but koa (Acacia koa) is also very common. Other trees include kāwau (Ilex anomala), alani (Melicope clusiifolia), ōhia ha (Syzygium sandwicensis), kōlea lau nui (Myrsine lessertiana), ohe (Tetraplasandra spp.), and olomea (Perrottetia sandwicensis) as well as hāpuu (Cibotium tree ferns). Apeape (Gunnera petaloidea), oha wai (Clermontia spp.), hāhā (Cyanea spp.), kāmakahala (Geniostoma hirtellum), kanawao (Broussaisia arguta), Phyllostegia spp., ākala (Rubus hawaiensis), kāmanamana (Adenostemma lavenia), Pilea peploides, māmaki (Pipturus albidus), olonā (Touchardia latifolia), and alaala wai nui (Peperomia spp.) are common understory plants. Vines include maile (Alyxia oliviformis) and hoi kuahiwi (Smilax melastomifolia). Iei.e. (Freycinetia arborea), puaakuhinia (Astelia menziesiana) and ōlapa (Cheirodendron trigynum) are epiphytic flowering plants found in wet forests. Epiphytic ferns, such as Adenophorus spp., ohiaku (Hymenophyllum recurvum), Ophioglossum pendulum, ākaha (Asplenium nidus), ēkaha (Elaphoglossum hirtum), and makue lau lii (Grammitis hookeri), cover trees. Epyphytic mosses include Acroporium fuscoflavum, Rhizogonium spiniforme, and Macromitrium owahiense. Loulu fan palms (Pritchardia spp.) may tower over the forest canopy.

Bogs

Bogs are found in montane regions where rainfall exceeds drainage. Dominant vegetation in bogs are shrubs, sedges, and grasses. Larger shrubs and small trees grow on bog perimeters or on raised hummocks. Carex spp., Oreobolus furcatus, and Rhynchospora rugosa are common sedges, shrubs include ōhelo kau laau (Vaccinium calycinum) and ōhelo (V. dentatum), while grasses are represented by Dichanthelium spp. and Deschampsia nubigena. Dwarf varieties of ōhia lehua (Metrosideros polymorpha vars. incana and glabriofolia) are the most seen trees on the edges of bogs. The ferns wāwaeiole (Lycopodiella cernua), amau (Sadleria spp.), and uluhe (Dicranopteris linearis) grow in bogs. Rare plants include liliwai (Acaena exigua), naenae (Dubautia spp.), and Argyroxiphium spp.