The Hawaiian Archipelago is the most isolated island chain on Earth, situated more than 2,000 miles from the nearest continent. This profound geographical separation allowed a few successful colonizing species to evolve without outside genetic influence for millions of years. The result is an extraordinary ecosystem characterized by high rates of species found nowhere else in the world. This unique environment, shaped by volcanic activity and diverse microclimates, has produced a complex native flora. Understanding Hawaiian plant life requires recognizing the distinct histories of species that arrived naturally versus those brought by humans.
Endemic and Indigenous Flora
Native Hawaiian plants are separated into two categories based on their geographic distribution. An indigenous species arrived naturally, without human assistance, and is found in Hawaii as well as in other parts of the world. In contrast, an endemic species is a native plant that evolved in Hawaii and exists nowhere else on the planet. Approximately 90% of Hawaii’s terrestrial native species are endemic.
This high rate of endemism is the product of adaptive radiation, a process where a single ancestral species rapidly evolves into diverse forms to fill various environmental niches. The Hawaiian lobelioids, comprising six genera and around 126 species, represent the largest family of flowering plants in the native flora. These plants have diversified dramatically in growth form, leaf shape, and habitat, ranging from small bog rosettes to dense forest trees.
The silversword alliance is another example, a group of about 30 species, including trees, shrubs, and vines, that all descended from a single North American tarweed ancestor. The iconic Haleakalā silversword, with its globe-shaped rosette and silver hairs, is adapted to the harsh, high-elevation, dry conditions of its volcanic habitat. Foundational elements of the native forests include the ‘Ōhi’a Lehua (Metrosideros polymorpha), often the first tree to colonize new lava flows, and the Koa tree (Acacia koa), which forms the canopy of many native forests.
Introduced Plant Life
The flora of Hawaii has been shaped by two major waves of human introduction, each serving a different purpose and having a different ecological impact. The first introductions were the “canoe plants,” species intentionally brought by Polynesian settlers for subsistence and cultural use. These approximately 27 species were selected for their versatility.
These introductions included staple crops providing essential starches, such as Kalo (taro) and ‘Ulu (breadfruit). Other culturally important plants were:
- Wauke (paper mulberry), cultivated for its inner bark to make Kapa (barkcloth).
- Kī (ti), used for religious offerings and wrapping.
- Niu (coconut), valued for food, water, and fiber.
These species were foundational to early Hawaiian society.
The second wave began after Western contact in 1778, resulting in the introduction of thousands of non-native species for agricultural and ornamental purposes. Many of these later arrivals have become invasive, posing the dominant threat to native ecosystems. Invasive species such as strawberry guava (Psidium cattleianum) form dense thickets that crowd out native plants and disrupt watershed function. The introduction of certain grasses, like Fountain Grass (Cenchrus setaceus), has increased the frequency and intensity of wildfires by providing highly flammable fuel. Other problematic species, like Faya tree (Morella faya), alter soil chemistry, while Miconia (Miconia crenata) blocks sunlight with its large, dense leaves.
Major Ecosystems and Plant Adaptations
The Hawaiian Islands feature a diversity of habitats created by the interaction of elevation, topography, and the rain shadow effect. This effect occurs when persistent trade winds push moist air up mountain slopes, causing it to cool and release precipitation on the windward side. The air that descends on the leeward side is significantly drier, creating a stark contrast between lush rainforests and arid shrublands.
Wet Rainforests
These ecosystems thrive on the windward slopes, receiving high rainfall that supports a dense, multi-layered canopy. Plant life is characterized by ‘Ōhi’a Lehua and Koa trees, with abundant epiphytes like ferns and mosses that capture moisture directly from the air.
Dry Forests and Shrublands
These occupy the leeward slopes, where plants have evolved adaptations to survive the low rainfall. These species often feature small, leathery, or waxy leaves to minimize water loss and may possess deep root systems to access groundwater.
Coastal Zones
These zones present challenges of salt spray, wind, and dry, sandy soil. Plants such as the indigenous ‘Ilima (Sida fallax) and Naupaka Kahakai (Scaevola taccada) tolerate the harsh conditions using thick, succulent leaves or specialized salt-excreting glands.
Alpine and Subalpine Zones
Located on the highest mountains, like Mauna Kea and Haleakalā, these zones are cold, subject to intense solar radiation, and have poor soil. The endemic silversword survives here by growing in a dense rosette, with its silver hairs reflecting sunlight and trapping heat.