Ontario Weeds: Nodding thistle
Excerpt from Publication 505, Ontario Weeds, Order this publication
Table of Contents
- Other Names
- General Description
- Stems and Leaves
- Flowers and Fruit
- Similar Species
- Related Links
Nodding thistle. Flower Head, on a naked (non-winged) stalk.
Nodding thistle. Dense stand of plants.
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.
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