Ontario
Weeds: Lady's thumb
Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Leaves
- Flowers and Fruit
- Caution
- Habitat
- Similar Species
- Related Links
Name: Lady's-thumb, Polygonum persicaria
L
Other Names: renouée persicaire,
Red shank, Smartweed, persicaire pied rouge, persicaire
Family: Buckwheat or Smartweed Family (Polygonaceae)
General Description: Annual, reproducing
only by seed.
Photos and Pictures
Lady's Thumb. A. Plant. B. Portion of stem with leafstalk
and ocrea. Pale smartweed. C. Portion of stem with lower
surface of leaf blade, leafstalk and ocrea. Pennsylvania smartweed.
D. Portion of lower stem with leafstalk and ocrea. E. Portion of
upper stem with leaf stalk and ocrea showing stalked glands.
Stems and Roots: Stems erect from a taproot,
20-100cm (8-40in.) high, green or reddish, smooth except for slightly
swollen at the distinct nodes; each node with a hairy ocrea (cylindrical
membranous sheath surrounding the stem).
Leaves: Leaves alternate (1 per node),
narrowly elliptic, 2-15cm (4/5-6in.) long, greenish above and slightly
paler below, usually with a reddish to brownish or purplish blotch
near the middle; undersurface of leaf often slightly rough with tiny
bumps, but never glandular or hairy, ocrea arising with the leafstalk
at each node, membranous and somewhat papery, its surface covered
with short, upward slanting hair and its upper margin ciliate with
a fringe of short, erect hair about 1-2mm (1/25-1/12in.) long.
Flowers & Fruit: Flowers small,
densely crowded into narrow cylindrical spikes (1-4.5cm, 2/5-2in.)
long at ends of stems and branches; each flower with 5 pinkish sepals
2-4mm (1/12-1/6in.) long, sometimes nearly white; fruits ("seeds")
more or less enclosed by the sepals when mature, shiny, smooth, black,
broadly ovate in outline, about 2mm (1/12in.) long; of 2 kinds, either
rounded-triangular or flattened or somewhat lens-shaped in cross-section;
the seed often slightly thickened near the middle. Seedling with cotyledons
(seed leaves) about 8-12mm (1/3-½in.) long by 2-3mm (1/12-1/8in.)
wide, tapered towards both ends, reddish on the undersurface; stem
below the cotyledons often reddish to brownish-green; cotyledons soon
withering on developing stems. Flowers from June to September.
Habitat: Lady's-thumb is an introduced
weed which occurs in cultivated land on nearly all soil textures throughout
Ontario as well as along roadsides and waste places.
Similar Species: It is distinguished from
other members of the Smartweed Family by the following combination
of characteristics: undersurface of leaves without matted white hair
or yellowish glands, ocrea with hair on the surface and a fringe of
longer hair on the margin, and the stem lacking glands on the upper
portion near the spikes of flowers. The reddish or purplish blotch
usually present on the upper surface of the leaves cannot be relied
upon as a distinguishing feature of Lady's-thumb. Occasionally it
is absent from this species and frequently can be found on leaves
of other species as well.
Caution: The seed is a frequent contaminant
in small grains.
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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