The author lives in a quiet seaside community in Puna on the Big Island of Hawaii. He's an avid gardener, traveler, and photographer.
Hawaii’s rainforests are home to diverse native trees and plants that thrive in the warm, wet, humid climate. Unfortunately, many non-native plant species have invaded Hawaii’s rainforests and are now spreading at an alarming rate!
The invaders are highly adaptable and fast-growing. They compete for soil nutrients, sunlight, and rainwater; crowd out native vegetation, and eventually dominate the landscape.
Some of the invaders are remarkably beautiful! Sadly, visitors to Hawaii might mistakenly think these are natural native species because they look so exotic and tropical!
Here are 11 unique invasive plants currently listed as top threats to Hawaii's rainforest ecosystem.
1. African Tulip Tree (Spathodea campanulata)
Also called Flame of The Forest, it is one of the most beautiful flowering trees in Hawaii. These magnificent trees grow abundantly in the forests, especially along streams and waterfalls. Their showy scarlet-orange flowers resemble tulips with ruffled petals. One variety (Spathodea campanulata ‘Aurea’) produces attractive clusters of golden yellow flowers.
Originating from Africa and introduced to Hawaii in the late 1800s, it was a popular garden plant until recently. The long, erect seed pods release hundreds of feathery seeds that would drift in the wind for miles! The seeds germinate quickly and create a dense thicket of seedlings on the forest floor. They will become big, tall trees in just a few short years! Young seedlings are easy to pull out of the ground; when they get older, it is much harder to remove due to their deep, extensive root system.
2. Miconia (Miconia calvescens)
Native to Central and South America, Miconia was first imported to Hawaii in the late 1950s as an ornamental species, well known for the attractive foliage: shiny oval-shaped leaves—green on top and purple underneath—with prominent symmetrical veins. Their small, pretty white flowers transform into clusters of grape-like fruits that contain thousands of tiny seeds. Studies have shown that a single plant can produce up to 3 million seeds in one year! Birds eat the fruits and disperse the seeds.
Considered highly invasive, Miconia is now spreading uncontrollably in many of Hawaii’s rainforests. Their large leaves form a dense canopy, inhibiting photosynthesis and blocking rainwater from reaching smaller species, like native ferns, growing on the forest floor.
3. Octopus Tree (Schefflera actinophylla)
Around the world, Schefflera is often used as an indoor potted plant to decorate homes and offices. However, it can rapidly grow into a 40-foot tree in tropical climates if planted outdoors! Schefflera is another "got away" ornamental species that wreaks havoc on the Hawaii rainforest ecosystem. Their reddish-maroon flower stalks look like the waving tentacles of an octopus, hence its common name.
It is a prolific seeder! If one seed landed on a nearby tree, it would sprout and become an epiphyte (a tree that grows on another tree). Eventually, it will strangle and kill the host tree with its thick, rope-like aerial roots! In Hawaii, Octopus Tree is adaptable and has a long life; it can grow happily on barren lava fields or rock cliffs along the shoreline.
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4. Autograph Tree (Clusia rosea)
Native to the Caribbean islands, Autograph Tree was widely used in Hawaii decades ago for urban landscaping projects. Unfortunately, it escaped into the wild and became one of the worst invasive trees in the state! It is known for its dark green, thick, leathery leaves, which people can engrave or "autograph" their names on top using a stick, pocketknife, or fingernail.
These magnificent trees can grow up to 50 feet tall; produce pretty pink blossoms which transform into round, pale green seed capsules. The seed capsules split open when matured, exposing the fleshy, reddish-orange seed pulps inside. Birds love to eat the pulp and are responsible for dispersing the seeds. Like Octopus Tree, the Autograph Tree often begins its life as an epiphyte, attaches itself to a host tree, and gradually smothers the life out of that poor tree!
5. Strawberry Guava (Psidium cattleianum)
Native to South America, the Strawberry Guava tree causes widespread damage to Hawaii’s rainforests due to its aggressive growth habit. It forms impenetrable dense shrubs, crowding out all other plants. It has no natural predators or diseases. Its suckers can quickly regrow from land burning or clearing. A cut branch would sprout roots if left lying on the ground or in a compost pile.
Also known as Cherry Guava, it produces several fruit crops a year. Ripe fruits are bright red and have a mouth-watering smell. The juicy flesh tastes sweet and tart, delicious when made into jams and jellies. Each fruit contains dozens of hard seeds. Feral pigs, rats, and birds devour the fruits and disperse the seeds. The seeds quickly germinate and grow into a mini forest of Strawberry Guava in no time!
6. Stink Vine (Paederia foetida)
Also known as Skunk Vine or Stink Maile, this tenacious vine—native to much of East Asia—crawls on the ground and grabs hold of every tree and shrub it can reach! It quickly climbs (by twining) up to the treetops, blanketing large sections of the forest canopy, blocking out sunlight and rainwater altogether! Its pointy, slender leaves emit a pungent, foul odor when crushed, hence its common name.
The flowers are very attractive: tubular-shaped, creamy white ruffled petals on the outside, red throat lined with purple hairs on the inside. They bloom profusely in the summer, followed by clusters of small brown berries containing seeds. Seedlings sprout up quickly; once established, they are very hard to get rid of.
7. Bingabing (Macaranga mappa)
Bingabing is one of the most peculiar invasive species in Hawaii. It grows prolifically in the forests and many other places, including parks, shorelines, beaches, and residential areas. Native to the Philippines, this plant is known for its giant (up to 2 feet wide) dark green leaves lined with pale green veins. A long, sturdy stem attaches to each leaf near its center, like an umbrella! Young leaves are smaller with a distinct copper brown color.
Bingabing can grow 20-30 feet tall, prefers sunny areas, and tolerates shady spots. The striking reddish-pink flowers appear in clusters at the top of the plant and develop into hundreds of seed pods.
8. Kahili Ginger (Hedychium gardnerianum)
Also known as Himalayan Ginger, this invasive plant also wreaks havoc on the Hawaii rainforest ecosystem. Kahiki Ginger thrives in fertile, moist soils, spreading rapidly by their large rhizomes (underground stems). They would take over a large area, forming dense, impenetrable patches 5-6 feet tall, smothering other vegetation, and preventing young seedlings of native species from growing.
Their flower spikes are spectacular: delicate, yellow butterfly-like petals with long red stamens. The flowers exude a heady, sweet perfume that attracts pollinating insects. Their red-orange seed capsules look equally attractive, often used in tropical flower arrangements. In Hawaii, Kahili Ginger flowers are made into leis to adorn hula dancers and brides at weddings.
9. Cup of Gold Vine (Solandra maxima)
This perennial tropical vine has other names, such as Golden Chalice or Hawaiian Lily. It's known for its enormous 6” to 8” cup-shaped yellow flowers with distinct purple stripes radiating from the center. The flowers have a slightly sweet fragrance that attracts bees and butterflies.
This fast-growing, semi-woody vine could climb up any tree and can reach over 70-80 feet high! Its aerial roots and tendrils sprout along the main vine and attach themselves to the host tree’s trunk for support. Native to Madagascar, Cup of Gold also grows as a large sprawling shrub, often seen along the roadsides in Hawaii. In addition to being an invasive pest, all parts of this vine are toxic to humans and animals.
10. Cane Tibouchina (Tibouchina herbacea)
Often mistakenly regarded as a native wildflower, this highly invasive herbaceous plant grows in large patches, commonly seen along the roadsides or newly disturbed areas. Native to South America, Cane Tibouchina belongs to the Melastomataceae family, which many members—including the infamous Miconia—have become noxious “superweed” in Hawaii.
One plant can produce numerous upright square stems 6 to 8 feet long. The delicate, pretty pink flowers bloom profusely year-round and turn into fuzzy seed capsules. Each seed capsule contains hundreds of tiny seeds! Birds and wind disperse them. Also, hikers and hunters may have the seeds stuck on their shoes and clothes, inadvertently transporting them to other parts of the forest!
11. Albizia (Falcataria moluccana)
The majestic Albizia has an old-world look, evoking nostalgia for a bygone era in Hawaii. Native to Papua New Guinea, it was imported to Hawaii in the mid-1800s to reforest defunct sugarcane plantations. Today, it grows everywhere, invading not only the rainforests but also pastures, farmlands, hillsides, valleys, and even residential subdivisions!
A mature Albizia can get more than 120 feet tall, towering above other trees; its canopy can spread over 100 feet wide. Interestingly, Albizia's branches are prone to break randomly, falling and crushing all other vegetation underneath the tree! Its root system is also relatively shallow; the whole tree could suddenly uproot and tip over during a rainstorm, causing significant damage to surrounding properties and infrastructures.
The author would like to thank the State of Hawaii Invasive Species Council and Big Island Invasive Species Committee (BIISC) for their public awareness and educational programs on invasive plant species.
All the plants featured in this article are currently listed on Hawaii’s Most Invasive Horticultural Plants by the Hawaii State Department of Land and Natural Resources.
© 2022 Viet Doan