Scarlet Spiral Flag Ginger, Indian Head Ginger, or Red Button Ginger (Costus woodsonii Maas), Hawaiian: ‘awapuhi ‘inikini po‘o – This species has gently spiraled stems and grows to about a meter in height. The leaves are deep green. The bracts of the inflorescence are bright waxy red, forming a pine cone-like spike (10-15 cm long) from which the yellowish-orange flowers protrude outward one at a time. The numerous small black seeds (1-2 mm long, the smallest of the true gingers) are usually dispersed by birds, but it is possible that they are also dispersed by water if the plant is growing in a wetland environment. C. woodsonii is an aggressive and invasive species. Its rhizomes spread rapidly and, once established, they are difficult to remove. This species grows well in full sun, flourishing even in the sandy soils and dune sands of tropical coasts, but it prefers the shade, ample moisture, and deep, fertile soil of the rain forest. Although the genus Costus sp. is found throughout the tropics on all continents, this species was first collected and described in Panama in 1941. It was an introduced ornamental garden plant that became a naturalized escapee in some parts of Hawaii. It is considered to be an invasive weed on Oahu, Maui, and Kauai islands. It is present in large but widely scattered populations at low elevations on Maui, particularly along the Hana Highway. This species also displays a classic behavior of species mutualism: it exudes what is known as “extrafloral nectar” from the bracts of the flower spike, attracting ant species that harvest the nectar. In turn, the ants protect the plant from the larvae of flies and other flying insects that lay their eggs in the flowers.
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