Canary Island St. Johnswort (Hypericum canariense)

Description:

Many-branched shrubs 1-4 m tall. Leaves oblong-lanceolate to narrowly ellipticlanceolate, 5-7 cm long, 1.2-1.6 cm wide, glabrous, glandular punctate with translucent glands, base cuneate to attenuate, sessile and somewhat amplexicaul. Flowers 2-3 in cymes terminating the upper stems, the cymes arranged in panicles, pedicels 10-20 mm long in fruit; sepals ovate to lanceolate, ca. 3 mmlong, apex acute to obtuse; petals yellow, spatulate, ca. 17-19 mm long, apex hooded; stamens 12-36, in 3 clusters; styles 3. Capsules coriaceous, ovoid, 3-lobed, apex truncate. Seeds numerous, pale reddish brown, elongate-cuneate, 1.4-1.6 mm long, reticulate.

Biology and Ecology:

Cultivation: Many species in the genus, Hypericum, are easily cultivated and grown from seeds as ornamentals for borders, rock gardens, shrubs and ground covers. H. canariense is widely cultivated for ornament in its native habitat, the Canary Islands and Madeira. It has numerous bright yellow flowers and a nice shrubby habit. In the United States, H. canariense is cultivated in southern states of at least California and Hawai’i. Though not widely grown in home gardens or as a landscape plant, H. canariense is sometimes grown in arboretums and botanical gardens. In addition, internet sources reveal that seeds of H. canariense are available for sale.

Invasiveness:In both California and Maui, Hawai’i, H. canariense is spreading from initial plantings. H. canariense is also listed in the global compendium of weeds for Western Australia, where it has recently been collected. In California, infestations form dense thickets and crowd out native and non-native vegetation. It is reported that the only native plants left after H. canariense invades are those that are at least 1.5 m tall. In addition, H. canariense can comprise 90- 100% of the vegetation cover in infested areas. Spread at a rate of up to 45- 90 m per year have been observed in favorable conditions in California. On Maui, numerous fine, light, wind dispersed seeds readily germinate along roads, in yards, open pastures, in gulches, on steep banks, and scrub areas. It seems to tolerate higher elevations and may be a potential invader to the upper slopes of Haleakala, Maui. Visiting botanists from the Canary Islands said that this plant will love our mountain.

Control Methods:

Physical control: Small seedlings can be pulled. Medium sized plants can be grubbed out. Larger plants are harder to pull or dig up, but it can be done. Plants will re-sprout if cut and not treated with an herbicide.

Chemical control: On Maui, plants in the way of road crews appear to be getting some control. We observed plants that appeared to have been cut at the base, rebounded, then sprayed with a foliar herbicide. These plants appeared damaged, but not totally dead. Plants on Maui have been successfully controlled with a basal bark application of triclopyr (Garlon 4). In addition, California information suggests that a cut stump herbicide application of glyphosate (Round Up) at full strength is an effective control method (TNC 2002). They suspect that lower concentrations may be effective, but have not done any trials.

Biological control: No biological control agents are currently known, though numerous biological control agents have been introduced to the United States to combat a related species, H. perforatum.

Cultural control:The public could be asked not to plant H. canariense or other potentially harmful non-native plants. Plants that are observed that are not within the current infestation zone can be reported.

Management Recomendations:

H. canariense is an aggressive invader in both California and Maui, Hawai’i. It is also present and being considered as a potential weed in Western Australia. In Hawai’i, the only known location in the state is in Kula, Maui. H. canariense seems to thrive in this dry, cool, upland environment and poses a potential future threat to upland native shrubland, grassland, gulches, and possibly some wooded areas of Haleakala. Currently, there is no established control campaign being waged against this aggressive invader. Without persistent and diligent control, H. canariense will continue to spread, possibly establish several infestation loci, and become more costly and difficult to manage in the future. This species could be a potential candidate for inclusion in the Hawai’i Department of Agriculture’s noxious weed list. This would prohibit transport and further planting. More intense surveys of the gulches above the current infestation on Maui would help refine the upper boundary. This would probably be best done around April or after rains when Hypericum is in full bloom which makes it easier to map. Information on distribution and weedy potential of other Hypericum spp. in the State and elsewhere would be useful. Other places in the world with similar habitat should take note that Hypericum canariense is likely to invade if planted.

Sourced From: www.cal-ipc.org › … › Invasive Plant Management › plant profiles