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QUESTION: We love beach heliotrope trees and they seem to be good survivors of our changing-climate planet with these crazy high tides, warm water and coastal erosion.
Can you tell us more about these pretty beachside trees?
— Moriwaki Ohana, Kaaawa
ANSWER: Tahinu or beach heliotrope trees are native to other Pacific islands but are an introduced plant in Hawaii. They sure look native, don’t they? Their silvery leaves and flowers and pea-size, greenish-brown, pointy fruit are happy growing in sand and exposed to sea salt-filled air. They have been in Hawaii a long time.
Many years ago, naturalist Lorin Gill said they were brought here by botanist Otto Degener because Degener thought they would thrive on our coasts, which they do. But I can’t find this in the literature, and Degener has died, leaving us a legacy of great reference books.
Tahinu is native to tropical shores from the Indian Ocean to the Pacific and is especially common on coral islands. In Hawaii, it has spread on the main islands, except Kahoolawe. Tahinu also grows in Papahanaumokuakea Marine National Monument, where it is found on Kure, Midway, Pearl and Hermes atolls, as well as Lisianski, Laysan and French Frigate Shoals. It was first collected on Oahu in 1864, and William Hillebrand, the first director of Foster Botanical Garden, reported it back then as a cultivated plant.
It is a less-thirsty plant and is pretty and tough in landscaped gardens.
Tahinu’s Latin name is Tournefortia argentea. It is in the Boraginaceae plant family and is related to our prized lei flower of Kahoolawe, hinahina, and to kipukai and kou.
When you look at the flower clusters of all these plants you can see they are plant “cousins.” The floral arrangement is called a helicoid cyme. It curls up like the new crozier of a fern and the buds uncurl in succession into flowers. Temperate plants like borage and forget-me-nots are also in this plant family.
Beach heliotrope leaves are eaten raw in India. My husband loves to point this out to visitors and keiki by happily munching on the leaves!
In the Tuamotu Islands of French Polynesia, legend has it that this was one of the first trees created.
I traveled to Wake Island for some arborist work recently and the tahinu are native and epic there. Talk about a survivor tree in a totally harsh environment!
Wake gets very little rain and the “soil” is coral rubble with maybe a thin layer of humus from leaf litter. It’s very hot, and plants that grow in Hawaii look very different there. The Wake tahinu are big and beautiful, providing nesting canopy for myriad seabirds. They protect the atoll from typhoon waves and winds.
Seeing them there reinforced for me how this would be a good tree for us in Hawaii as the ocean levels rise and our coasts are battered by higher waves, even the high tides that occur with every full moon. We should get busy and propagate lots of them, as well as hala, or pandanus. Restoring vegetated sand dunes to coastal areas, homes and beach parks could help us buffer and protect our coastal areas.
Associate professor and landscape specialist Andy Kaufman at the University of Hawaii’s College of Tropical Agriculture and Human Resources and his graduate students have been doing some excellent plantings and research on the tahinu at Bellows Air Force Station and other coastal areas. Kaulunani Urban and Community Forestry Program, a nonprofit that aids our urban and community forests, has helped support Kaufman’s research.
Heidi Bornhorst is a sustainable landscape consultant specializing in native, xeric and edible gardens. Reach her at heidibornhorst@gmail.com.
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