Botany Blueprint: The Hawaiian Cotton Tree

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Specimen #21: Hawaiian Cotton Tree (Kokia drynarioides)

 The Hawaiian Cotton Tree

Although it is an ancestor of the well-traveled modern cotton, Kokia drynarioides, a Hawaiian endemic, has most likely not left the island on which it evolved. You might say there are worse places to be bound, than a sunny spot on leeward Hawai’i, but botanists consider it a problem and a puzzle. The tree is critically endangered, and its seed dispersal strategies are a mystery—in short, how can it repopulate itself amidst environmental pressures?

How about a water dispersal strategy? Yes, the seeds seem designed float—even for several days, before the fibers become heavy with water, which is long enough for dispersal throughout the archipelago by oceanic drift. In theory. In reality, the tree has been found no where but on the island of Hawai’i—and only in limited areas, in a dry, rocky environment with little consistent water. Botanists concede that seasonal flash floods might have distributed the seeds throughout the island, but no one’s really sure.

Putting aside the seed dispersal mystery, it’s fair to say that the tree is otherwise well-adapted to its habitat. Kokia drynarioides is hardy, and it has evolved with the island.

It adapted to the nutrient-depleted soil on Kona’s lava fields, and developed a symbiotic relationship with its primary pollinator (the flower’s nectar pools at the bottom of an angled blossom that is perfectly designed for the curved beak of the Hawaiian honey-eater). Captain Cook and his naturalist collected the plant in the late 1700s, and it was placed in the cotton (Gossypium) genus. Since then, it’s been given its own genus (Kokia), and common names: the Hawaiian Tree Cotton, hau Hele’ula, (meaning ‘rubescent hibiscus’), and kokio.

Historically, Hawaiians used the plant’s bark to dye their fishing nets, but they’ve had little interest in the seeds.

Today, the environment with which the species evolved has changed, and kokio is nearly extinct in its native habitat. As of 2010, fewer than six individuals were counted in the wild. Its environmental pressures are numerous. Most notably, two introduced species have reduced populations.

First, a wild grass that covers the lava fields, inhibiting kokio growth and increasing the frequency of wildfires. Second, a species of arboreally agile rats, introduced in the 1800s, will climb the trees and eat the seeds right from the branches. Those seeds that do survive the rat and maneuver around the fountaingrass, successfully germinating into saplings, are gobbled up by grazing cattle and goats. And those seeds that make it past the rats, cattle, and goats? Well, it’s not certain how they disperse.

Botanists are monitoring populations and making lists of what to do, with emphasis on seed dispersal studies. Initiatives to cultivate the tree have been underway since the early 1900s, when botanists first recognized the tree’s critical status. Seeds were collected seeds and dispersed to gardens and arboreta. Today, the Amy B. H. Greenwell Ethnobotanical Garden, in Kona, is one of the island’s primary kokia caretakers. Horticulturalists have cultivated several individuals that grow alongside the native poppies, Koa, and taro. One kokia tree was fruiting when I visited. It wore its fruits like a shawl of baubles, each arrangement with five seeds, all of them cut with two facets and a golden-red radiance. Many of the seeds had already been released, but the Garden’s director allowed me to inherit several that remained. It’s no ersatz strategy to disperse the tree’s seeds, but one to share its story.

See the rest of Anna Laurent’s Botany Blueprint series here.

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