Family: Costaceae
Costus woodsonii, commonly known as Indian head ginger, red spiral flag, or scarlet spiral flag, is a tropical ornamental plant native to Central America. It is prized for its upright, spiraling stems and showy, cone-shaped red flower bracts that produce small yellow blooms. This lush, ginger-like plant is often used in landscaping and gardens for its bold color, tidy growth form, and ability to thrive in warm, humid environments. It is frequently planted as an accent plant, along borders, or in tropical-themed landscapes.
In Hawaiʻi, Costus woodsonii is naturalized on Maui and potentially naturalizing on Kauaʻi and Hawaiʻi Island, indicating it is spreading beyond cultivation. This species possesses traits that are cause for concern, including the ability to reproduce vegetatively and tolerate a range of growing conditions. If left unmanaged, it could escape gardens and detrimentally impact tropical island ecosystems by forming dense stands and displacing native vegetation. To help protect Hawaiʻi’s unique environments, choosing a low-risk ornamental or a native plant alternative is strongly recommended.
High Risk Traits:
- Naturalized: Escaped and established in Hawaii and Cook Islands.
- Forms thickets: Creates dense stands that can outcompete natives.
- Climate match: Suited to tropical/subtropical zones.
- Multiple introductions: Widely cultivated as an ornamental.
- Versatile establishment: Tolerates shade and a range of soils.
- High reproductive output: Reproduces by seed and vegetative plantlets.
- Rapid lifecycle: Can reproduce in less than a year.
- Self-compatible: Does not require a mate to produce seed.
- Bird-dispersed: Seeds are eaten and spread by birds.
Low Risk Traits:
- Not weedy: No evidence as a major agricultural or environmental weed.
- Low seed numbers: Seed is produced "sparingly," not prolifically.
- Specialist pollinator: Primarily relies on hummingbirds for pollination.
- Not toxic: Safe for humans and animals.
- No physical defenses: Lacks spines, thorns, or burrs.
- Low accidental spread: Seeds unlikely to hitchhike on gear or vehicles.
- Not invasive in all areas: Limited reports of widespread invasion.
