Ontario Weeds: Nodding thistle

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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 Leaves
  6. Flowers and Fruit
  7. Habitat
  8. Similar Species
  9. Related Links

Name: Nodding thistle, Carduus natans L.,

Other Names: CRUNU, chardon penché, Musk thistle

Family: Composite or Aster Family (Compositae

General Description: Biennial, reproducing only by seed.

Photos and Pictures

Nodding thistle. Flower Head, on a naked (non-winged) stalk.

Nodding thistle. Flower Head, on a naked (non-winged) stalk.

Nodding thistle. Dense stand of plants.
Nodding thistle. Dense stand of plants.

Nodding thistle. A. Basal rosette. B. Flower head on naked stalk.
Nodding thistle. A. Basal rosette. B. Flower head on naked stalk.

Stems & Leaves: Stems of second-year plants erect, 30-180cm (1-6ft) high, with harshly spiny, irregularly lobed, leaf-like wings running lengthwise on all stems and branches except just below each flower head; first-year plants forming a large, circular, nearly flat rosette, each leaf often 30cm (12in.) long by 10cm (4in.) wide, bright green to gray-green, margins deeply lobed, the lobes close together, twisted and wavy, with long, sharp spines pointing in all directions; the actual upper and lower surfaces of the leaf blade and its lobes (apart from the harshly spiny margins) finely woolly-hairy and soft to the touch; stem leaves of second-year plants similar to rosette leaves but gradually smaller and less lobed upwards, alternate (1 per node).

Flowers & Fruit: Flower heads single on slender, smooth, long, bare (not spiny-winged) stalks at ends of branches and from axils of upper leaves, each head large, 4-7.5cm (1½-3in.) across but occasionally smaller, with no ray florets but with many, large, bright purple disk florets, these surrounded by an involucre of many, overlapping, broad-based, greenish bracts with outward- or backward-pointing, long, sharp spiny tips; heads at ends of stems and branches usually bent to one side ("nodding"), those from leaf axils often nearly erect; seeds light brown, shiny, 4mm 1/6in. long, egg-shaped with a small knob at the tip and a pappus (parachute) of short, unbranched (non-plumose), light beige hairs. Flowers from June to October.

Habitat: Nodding thistle is common throughout southern Ontario in pastures, waste places, roadsides and around buildings, especially on coarse-textured soils.

Similar Species: Flowering plants are distinguished by their large, showy, bright purple flower heads surrounded by an involucre of broad-based bracts narrowed to long, sharp, outward- or backward-pointing spiny tips and their heads nodding on long, non-winged stalks at ends of stems or upright in leaf axils (compare with Plumeless thistle); non-flowering plants and first-year rosettes are distinguished by their deeply lobed, bright green to gray-green leaves, the lobes much twisted, wavy and spiny margined, and both upper and lower surfaces (apart from the spiny margins) always finely woolly-hairy and soft to the touch, in contrast to the harshly, almost prickly-hairy surfaces of Bull thistle. Plants which seem to be intermediate between Nodding thistle and Plumeless thistle may be hybrids between these two species.

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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