Things Not to Touch in Your Woodlot

Some plants found in your woodlot are best left alone.  Mother Nature has provided these plants with certain chemical toxins in their leaves that may cause rashes, hives, swelling, and itching when they come into contact with your skin.

Members of the plant family Rhus (e.g., poison ivy, poison sumac) can cause allergic dermatitis.  This is when the body has an allergic reaction that may not be noticeable for a couple of days and may affect areas of the skin that were not exposed to the plant.  Other plants such as stinging nettles, cause a chemical dermatitis. This isn't an allergic response, but rather it is the result of a chemical contained in the plant (e.g., the formic acid in the stinging nettles). 

Some of these plants are very common and may be well-known to most woodlot owners, while there are a couple of plants that are not as common.  Read on to learn more about some of the things not to touch in your woodlot.

Poison Ivy (Rhus radicans ssp.)

One of the most common plants that will cause skin irritation is poison ivy.  It can be found throughout Ontario on sandy or stony sites, almost anywhere in your woodlot — along the forest edge, in meadows, forest openings and in the understory.

Poison ivy is a perennial that spreads by seeds and woody rhizomes. It can be found either as a ground plant measuring 5–120 cm high (Rhus radicans ssp. rydbergii) or as an aerial-rooted vine (Rhus radicans ssp. negundo) that climbs rough surfaces, such as a tree trunk, up to heights of 15 m.

Its leaves are glossy green, alternate and consist of three leaflets with the middle leaflet having a stalk much longer than those of the two lateral leaflets. The edges of the leaflets may be smooth or toothed, but they are rarely lobed. It may be confused with fragrant sumac, which has three leaflets, but has no extended middle petiolule. Virginia creeper has five leaflets instead of three.

Poison ivy is a very common cause of allergic contact dermatitis. It contains the potent antigen urushiol, which will sensitize 60 to 80 percent of the people who are exposed to it. It should be noted that the oil resin released from the plant (from the leaves, root and stem) may be carried on the fur of pets, clothing, shoes, or other objects, and then transferred to the skin.

Giant Hogweed (Heracleum mantegazzianum)

Giant hogweed is a member of the carrot family and looks similar to cow parsnip.  However, its size makes it stand out. This invasive plant can reach heights of 4–5 metres and has a reddish-purple stem measuring from 5–10 cm in diameter.  It flowers from June to September and has a large compound umbel measuring up to 1.1 metres across.  Each umbel will have 30–20 flowers.

If you come in contact with this plant you could experience severe burns to your skin. The sap found in giant hogweed contains furocoumarins (or psoralens) that cause phytophotodermatitis, a serious skin inflammation activated by exposure to the sun.

Giant hogweed can be found along roadsides and stream banks and has been reportedly found in Norfolk, Wellington, and Simcoe counties and the Muskoka region of southern Ontario.

Poison Sumac (Toxicodendron vernix)

Poison sumac is an uncommon woody shrub (small tree) that grows 2–7 metres in height and may be found in wooded swamps of southwestern Ontario.  This plant contains the antigen urushiol, similar to that of poison ivy, and contact with the plant will irritate the skin.

Identification features include large alternate leaves usually with 9–13 toothless leaflets and a red rachis (the stem connecting the leaflets).  The leaflets are smooth, pointed and may have a shiny surface.  The foliage has brilliant orange or scarlet coloring in the fall. 

Although the leaves of both poison sumac and nonpoisonous species of sumac are similar, there are some key differences in their fruits.  Poison sumac has clusters of small yellowish-green flowers that produce whitish-green coloured fruit that hang in loose clusters, about 10–30 cm in length, whereas nonpoisonous species of sumac have red fruit that form distinctive, erect and cone-shaped terminal heads.  Also, the fruit on poison sumac grows between the leaf and the branch.  Nonpoisonous sumac has fruit growing from the ends of its branches.

Wild Parsnip (Pastinaca sativa)

While wild parsnip occurs throughout Ontario, it is particularly abundant in eastern Ontario and it appears to be spreading westward.  It will slowly invade an area, and once a population builds, it will aggressively spread throughout the entire area. 

Generally found along the edges of plantations, roadsides, meadows and in old pastures, wild parsnip is a biennial plant that is only reproduced by seed.  It grows 50–150 cm high, has compound leaves (two to five pairs of leaflets — three to five cm long) that are arranged alternately on the stem; the leaflets are somewhat mitten-shaped.  Its flowers are yellow, form a flat-topped umbrella-like cluster (12–20 cm across), and are present from late May to early fall. One other characteristic feature of this weed is its distinctive parsnip odour.

It may be confused with other members of the carrot family like cow parsnip, which has white flowers in umbels, or poison hemlock that has finely divided leaves and small compact umbels.  Remember, wild parsnip has pinnate leaves with yellow flowers and a distinctive parsnip odour.