Invasive Plant Species

WARNING: Exposure to Giant hogweed's clear watery sap, in addition to sunlight, can result in severe burns and blistering to the affected areas.

If you are exposed to Giant hogweed:

  • Wash the affected area immediately with soap and water
  • Keep the area out of the sun for at least 48 hours
  • Seek medical advice for burns

Giant hogweed is an Asian member of the Parsley or Carrot Family. It closely resembles our native plant cow parsnip, except the taller giant hogweed grows up to 6 metres or more. It was first introduced as an ornamental feature plant, but its persistent and invasive characteristics quickly made it an escaping garden pest that has spread throughout the Lower Mainland and North America. Mature plants can reach up to 5 m high and produce up to 100,000 seeds which are viable for 7 to 15 years.

Introduced from Asia in the 1800's, Japanese knotweed was considered an attractive and harmless shrub. However, through the ever-increasing disturbance of natural areas, this aggressive perennial soon established its invasive foothold. Reaching heights of up to 3.3m (10 ft) tall, Japanese knotweed has the ability to over-shadow and out-compete all plants within its reach, reducing the ecological integrity of an area.

English ivy is an evergreen vine native to European forests and introduced into North America around 1723 as a horticultural plant. Unfortunately English ivy has not remained in the environment for which it was intended. It has spread to many natural areas and is increasingly becoming recognized as a danger to natural ecosystems.

Contrary to its common name, Himalayan blackberry is a native of western Europe. It was probably first introduced to North America in 1885 as a cultivated crop. By 1945 it had become naturalized along the West Coast. Himalayan blackberry occurs mainly in areas with an average annual rainfall greater than 76 cm, at altitudes up to 1800 m, on both acidic and alkaline soils. The shrubs appear as "great mounds or banks" suffocating native vegetation.

English holly is an escaped ornamental species common in North Vancouver and is known to invade upland forests and the edges of wetland areas. It is found throughout Mahon Park.

English holly damages riparian forests and native vegetation by consuming more nutrients than it replaces. The leaves are slow to decompose, hence nutrients are biologically unavailable to other native plant species.

Clematis has become a serious problem in some areas in Mahon Park as it has the ability to smother and eventually bring down large trees. Attractive, scented creamy-white flowers in summer are followed by seeds with long, fluffy hairs, which can be spread either by wind, or by floating on water.

Lamiastrum is sold in nurseries and garden stores as a desirable ornamental vine for hanging baskets but once Lamiastrum gains a foothold outside of a hanging basket arrangement, it is very difficult to keep under control. Beautiful as it is, this trailing creeper has the tendency to sneak over backyard fences and invade our natural area. By forming a dense blanket of leaves, it out-shades practically every other plant on the forest floor.

Common periwinkle is native to Europe and was first introduced into North America in the 1700s as an ornamental. It is still commonly sold as an ornamental ground cover. This trailing vine reaches lengths up to 3 feet. The stems are slender, somewhat woody and green in colour. The opposite, glossy leaves are approximately 1 inch long and narrowly elliptical in shape. Some varieties have variegated leaf colours. Flowers are violet to blue (possibly white) in colour, 1 inch wide, and 5-petaled. Common periwinkle invades open to shady forests, forming dense and extensive mats along forest floors that exclude native vegetation.

Bishop's weed is an aggressive groundcover that spreads by rhizomes and provides a dense canopy of foliage up to 12" in height. Small white flowers are produced in umbels similar in form to Queen Ann's lace, but aren't as showy. It quickly develops into a dense groundcover suppressing Native plants.

Himalayan balsam is native to the Himalayan region of Asia. It has escaped garden cultivation to invade many areas, predominantly river edges, riparian areas and wetlands. This pretty pink flowering invader is currently found throughout the Lower Mainland and Fraser Valley of BC. Policeman's helmet is wreaking havoc upon native plants with devastating effects. Each plant can produce up to 800 seeds that burst from mature seedpods travelling over 21ft (7m).

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