Ontario Weeds: St. john's wort
Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Flowers and Fruit
- Habitat
- Caution
- For more information...
Name: St. John's-wort, Hypericum perforatum
L.,
Other Names: Goatweed, Klamathweed, millepertuis
perforé, millepertuis commun, herbe Saint-Jean
Family: St. John's-Wort Family (Hypericaceae)
General Description: Perennial, reproducing
by seed and by spreading underground roots or rhizomes. It is distinguished
by its almost woody base, opposite leaves, bright yellow flowers, and
leaves with transparent dots.
Photos and Pictures
A. Plant. B. Pairs of leaves showing transparent dots.
St. John's wort. A.
Top of flowering stem. B. Single leaf showing scattered, transparent dots.
St. John's wort.
C. Basal crown and root.
Stems & Roots (2 kinds):
- upright flowering stems 40-80cm (16-32in.) high, tough or woody near
the base, branching and smooth except for shallow ridges below the base
of each leaf;
- horizontal basal branches, these produced in late fall or early spring,
short, densely leafy, and radiating out from the basal crown of each
plant; leaves opposite (2 per node), stalkless, elliptic or linear,
smooth-margined and, when viewed against the light, appear to have many
small perforations or transparent dots.
Flowers & Fruit: flowers numerous in clusters
at ends of branches; each flower, about 2cm (4/5in.) across, has 5 yellow
petals with several, small, black dots along the margins, many stamens in
3 clusters and a single pistil in the centre; seedpods splitting from the
tip; seeds dark brown about 1mm (1/25in.) long. Flowers from June to August;
seedpods frequently persisting all winter.
Habitat: St. John's-wort occurs throughout
Ontario in pastures, edges of woodlots, roadsides, abandoned fields, waste
areas and occasionally in lawns and flower borders.
Caution: If eaten by livestock, St. John's-wort
may cause photosensitization, a condition in which patches of white or light-coloured
skin become seriously sunburned under normal exposure to sunlight. Avoid
pasturing animals where this weed is abundant or keep them under shade during
normal sunny days.
For more information...
... on weed identification, order OMAFRA
Publication 505: Ontario Weeds
... on weed control, order OMAFRA
Publication 75: Guide To Weed Control
...on weeds in field crops, contact Mike Cowbrough (mike.cowbrough@ontario.ca),
Weed Management Specialist (Field Crops), OMAFRA
...on weeds in horticultural crops, contact Kristen Callow (kristen.callow@ontario.ca),
Weed Management Specialist (Hort Crops), OMAFRA
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