Family: Amaryllidaceae
Agapanthus praecox (common agapanthus, blue lily) is a popular ornamental plant that poses a significant ecological threat to Hawaiʻi’s landscapes. Originally from South Africa, it is a hardy, clumping perennial known for its striking blue or white flower clusters. Despite its beauty, it is a highly invasive species that has become a serious environmental weed in regions with similar climates, such as Australia, New Zealand, and Tasmania. Its ability to tolerate a wide range of conditions—including drought, salt, wind, and poor soil—makes it particularly adept at escaping cultivation and invading natural areas.
Once established, common agapanthus forms dense, extensive stands that crowd out native vegetation, leading to severe biodiversity loss. It spreads aggressively both by seed, which are dispersed by wind and water, and by its tough, resilient rhizomes that resprout if disturbed. Manual removal is difficult and herbicides are often ineffective, making control a major challenge. In Hawaiʻi, Agapanthus praecox is cultivated but not currently known to be naturalized. To protect Hawaiʻi’s native ecosystems, it is strongly recommended to avoid planting this species and to remove existing plants before they can spread into sensitive natural areas.
High Risk Traits:
- Invasive: Naturalized and damaging in Australia, New Zealand, and Tasmania.
- Environmental Damage: Forms dense monocultures that exclude native plants.
- Highly Tolerant: Tolerates frost, drought, poor soil, salt, and wind.
- Multiple Reproduction: Spreads effectively by seed and vegetative rhizome fragments.
- Effective Dispersal: Seeds are easily dispersed by wind and water.
- Hybridizes: Freely crosses with other agapanthus species, increasing adaptability.
- Persistent: Benefits from fire and is difficult to control with herbicides.
- Toxic: Sap is toxic to humans, causing severe mouth ulceration.
Low Risk Traits:
- Not Shade Tolerant: Requires full sun to flower, limiting forest invasion.
- Limited Dispersal: Not spread by birds, animals (externally), or as a produce contaminant.
- Not a Congeneric Weed: No other major weedy species in its genus.
- Lacks Specific Advantages: Not parasitic, allelopathic, spiny, or nitrogen-fixing.
