Ontario Weeds: Spotted water hemlock

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Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Name
  2. Other Names
  3. Family
  4. General Description
  5. Stems and Roots
  6. Leaves
  7. Flowers and Fruit
  8. Habitat
  9. Similar Species
  10. Caution
  11. Related Links

Name: Spotted water-hemlock, Cicuta maculata L.,

Other Names: carotte à Moreau, Beaver poison, Musquash-root, Poison parsnip, Spotted cowbane, Spotted-hemlock, Water-hemlock, cicutaire maculée

Family: Carrot Or Parsley Family (Umbelliferae)

General Description: Perennial, reproducing only by seed.

Photos and Pictures

Spotted water hemlock (A - plants in a marshy area; B - plants before flowering showing twice-compound leaves and horizontal thickened tuberous roots).

Spotted water hemlock (A - plants in a marshy area; B - plants before flowering showing twice-compound leaves and horizontal thickened tuberous roots).

Stems & Roots: Stems erect, 1-2m (3-6½ft) high, hollow except for a partition at each node, round or slightly angular with purplish lengthwise streaks; base of stem slightly swollen and usually with several, narrow cross-partitions separating thin cavities, these visible by splitting the lower stem lengthwise downwards through the base; the freshly split surfaces usually soon developing little droplets of an amber or yellowish oily secretion; the swollen base usually surrounded by 3 or more fleshy, thickened, tuber-like roots which taper into long thin strands.

Leaves: Basal leaves at least twice compound, that is, each leaf divided once into 3 or more parts and each of these parts divided again into smaller parts or leaflets, occasionally these again redivided into still smaller parts or leaflets; the veins in each leaflet going to the notches between teeth on the margins; leafstalk long, thin, often somewhat channeled and always broadened at the base and partly surrounding the stem at the node; stem leaves alternate (1 per node), usually twice compound but leaves in the inflorescence frequently only once compound into 3 or 5 leaflets.

Flowers & Fruit: Flowers individually small, white, in compound umbels at ends of the stems and branches, 1 large umbel made up of several small, simple umbels or umbelets; each compound umbel flattish or rounded across the top and up to 12cm (5in.) in diameter but never spherical, usually without bracts or with only 1 or 2 bracts at its base; fruit a pair of oval or oblong, yellowish-brown "seeds" 2-4mm (1/12-1/6in.) long with prominent, rounded, brownish, lengthwise ribs on the outer surface. Flowers from June to August.

Habitat: Spotted water-hemlock is a native plant throughout Ontario, occurring in wet meadows, pastures, ditches, edges of streams and rivers, and swampy areas.

Similar Species: It is distinguished by the combination of its twice-compound leaves, base of split stem showing alternate narrow cross-partitions and thin cavities, and thickened tuberous roots surrounding base of stem; also by its white flowers in flattish compound umbels up to 12cm (5in.) across, these without any or sometimes with 1 or 2 bracts immediately below the umbel and the veins in each leaflet going to the notches between teeth on the margins.

Caution: Spotted water-hemlock is the most poisonous of all Canadian plants to both human beings and livestock, all parts of the plant being poisonous. Extreme care must be taken when pasturing areas where this plant grows, and in collecting wild greens, roots or seeds for human consumption.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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