Ontario
Weeds: Spiny annual sow thistle
Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Flowers and Fruits
- Habitat
- Similar Species
- Related Links
Name: Spiny annual sow-thistle, Sonchus
asper (L.) Hill,
Other Names: laiteron rude, Prickly annual
sow-thistle, laiteron âpre, laiteron épineux
Family: Composite or Aster Family (Compositae)
General Description: Annual, reproducing
only by seed.
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Photos and Pictures
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Spiny annual sow-thistle. A. Base of plant.
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B. Leaf from lower or mid-stem. C. Top of flowering stem.
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Stems & Roots: Resembling Perennial
sow-thistle in general appearance but distinguished from it by its
annual root (tapering downwards from ground surface and not connected
to a strong horizontal root that has other buds), lower and middle
stem leaves rather firm, clasping the stem with prominent rounded
lobes; all margins with small, moderately spiny teeth.
Flowers & Fruit: Upper stems and
involucral bracts of the flower heads smooth or sparsely glandular-hairy
and the flower heads smaller. Before opening, the flower heads are
short and cylindrical. When fully open they are about 2cm (4/5in.)
across and, after the yellow ray florets shrivel and fall, the heads
become top-shaped with a broad base and a narrow tip. Seeds brown,
3mm (1/8in.) long, somewhat flat with several lengthwise ribs on each
surface but without cross-wrinkles, each with a fluffy white pappus;
whole plant with sticky white juice. Flowers from June to September.
Habitat: Spiny annual sow-thistle occurs
throughout Ontario in waste places, along fence lines, roadsides,
around buildings and occasionally in gardens.
Similar Species: It is distinguished by
the rounded, clasping basal lobes on its rather firm leaves, the leaves
lobed and generally tapering towards the tip, its tapering annual
taproot, its small flower heads, and its seeds with lengthwise ribs
but not cross-wrinkled.
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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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