Plants that you don't want to touch
Poison Ivy (Rhus radicans)
Likely the most common and familiar of these three plants, poison ivy is widespread throughout Ontario in forests, fencerows, meadows, roadsides and natural areas.
Plant form: Grows in patches on the ground, or climbs fences, trees or buildings. The tall climbing form is mainly confined to areas along Lakes Erie, Ontario and the lower Ottawa valley
Life cycle: Perennial, spread by seeds (dispersed by birds) and by underground woody rhizomes. Stems also root in contact with soil.
Appearance: A deciduous woody vine with 3 leaflets (hence the saying "Leaves of three - let it be"). The longer petiole on the centre leaf is an identifying characteristic. Leaves are shiny green all summer, turning bright red in the fall. Clusters of white berries are produced by late summer and may be retained on the stems all winter.
Caution: All plant parts are poisonous, including roots, stems and leaves. The oil resin may be released onto clothes, pets, or prunings. Sensitive individuals need to use extreme care year-round. Inhaling smoke from burning plants can cause severe reactions in breathing passages.
May be confused with: Fragrant sumac - which has 3 leaflets, but no extended middle petiole; Virginia creeper - which has 5 leaflets instead of 3.
Figure 1 - The three leaves of Poison Ivy, note the centre leaf has the longer petiole (stalk)
Figure 2 - Berries of Poison Ivy
Figure 3 - The 5 leaflets of Virginia creeper, which often gets confused with poison ivy
Giant Hogweed (Heracleum mantegazzianum)
This member of the Carrot family has gained notoriety from recent reports in the media. It's a distinctive looking plant in the landscape now as a mature plant along roadsides, streambanks, and waste areas.
Life cycle: Perennial, reproducing only by seed. Giant Hogweed is a monocarpic plant, meaning it only produces seed once in its lifetime.
Appearance: Within an established stand there will be great variability in plant age and size with younger plants being less than 30 cm in height while older plants can be as high as 5 m tall, with a hollow reddish- purple stem up to 10 cm in diameter. Flowers from June to August, generally plants are taller than 2 m when flowering, with a compound umbel up to 1.2 m across, with 30 to 50 branches, each with an umbel with 30-20 flowers.
Caution: Giant hogweed contains furocoumarins (psoralens), which make human skin hypersensitive to sunlight, causing cellular damage at the surface. They absorb long-wave ultraviolet light and become photodynamic.
Figure 4 - The large compound leaf of Giant Hogweed
Figure 5 - The red/purple blotchy and hairy stem of Giant Hogweed compared to the relatively green and hairy stem of Cow-parsnip.
Figure 6 - A very tall and mature stand of Giant
May be confused with:
|Author:||Mike Cowbrough - Weed Management Specialist (Field crops)/OMAFRA; Kristen Callow - Weed Management Specialist (Hort)/OMAFRA; Leslie Huffman - Apple Specialist/OMAFRA|
|Creation Date:||28 July 2010|
|Last Reviewed:||28 July 2010|