Family: Hypericaceae
Origin, Description & Uses:
Hypericum canariense, commonly known as Canary Island St. Johnswort, is a shrubby flowering plant native to the Canary Islands. It is valued as an ornamental for its bright yellow, five-petaled flowers and soft, gray-green foliage, which give it an attractive, airy appearance in landscapes. This species can grow as a woody shrub or small tree and is often used in gardens for hedges, borders, or erosion control on slopes due to its dense growth habit and tolerance of dry, sunny conditions.
Risks & Threats:
This species is naturalized on Maui and possesses traits that are cause for concern in tropical island ecosystems. Hypericum canariense can spread beyond cultivation, forming dense stands that may outcompete native vegetation for light, water, and nutrients. Its ability to establish in disturbed areas and persist in dry environments increases its potential to alter native plant communities and ecosystem processes. Because of these risks, it could detrimentally impact Hawai‘i’s unique ecosystems. If intentionally cultivated, it is recommended to choose a low-risk or native alternative to help prevent further spread and protect local biodiversity.
High Risk Traits:
- Naturalized in California, Hawaii, and Australia
- Environmental weed; outcompetes native vegetation
- Congeneric weeds exist (other Hypericum spp. are serious weeds)
- Forms dense thickets (90–100% cover)
- Rapid spread (45–90 m/year)
- Self-compatible (self-pollinating)
- Reproduces via rhizomes
- Produces hundreds of viable seeds per capsule
- Prolific seed production (>1000 seeds/m²)
- Resprouts after cutting
- Creates fire hazard in dry environments
- Dispersed intentionally by people (ornamental sales)
Low Risk Traits:
- No spines, thorns, or burrs
- No toxicity to animals or humans
- No allelopathic or parasitic traits
- Not shade tolerant
- No bird or animal dispersal
- No produce contamination risk
- Well controlled by herbicides (glyphosate, triclopyr)
