Smartweeds, Knotweeds and
Black bindweed or wild buckwheat
Family: Smartweed/Buckwheat
Genus: Polygonum
Ocrea (leaflike tubes surrounding the stem at the nodes) assist in identifying specific speces.
Smartweed, pale or nodding
P. lapathifolium
Native to Ontario
Annual
Height: Usually up to 90 cm but can be 2 m
Habitat: Damp disturbed sites
Blooms: June to August
Flower: less than 2.5 mm in a dense spike, sometimes drooping, up to 10 cm. May be pink or greenish-white.
Ocrea: hairless
Lady's thumb
P. persicaria
Introduced
Annual (reproduced only by seeds)
Height: up to 1 m
Habitat: Roadsides and waste places
Blooms: June to September
Flower: 2-4 mm, 5 pinkish sepals, arranged in a spike up to 4.5 cm.
Ocrea: hairy
The term "Lady's thumb" refers to dark blotches on the leaves. However, this may be absent in P. persicaria and sometimes present in P. lapathifolium. So this feature is not a reliable means of identification.
Smartweed, swamp
P. coccineum
Native to Ontario
Annual (reproduces by seed and rhizomes)
Height: up to 90 cm
Habitat: Ponds and shorelines - may be aquatic or terrestrial
Blooms: July to September
Flower: up to 4 mm in a spike up to 18 cm.
A much deeper pink than the above species.
Ocrea has no leaf-like flange.
Knotweed, prostrate
P. aviculare
Introduced
Height: Up to 30 cm. Creeps along the ground forming a mat. Can become more upright in better soil.
Habitat: Waste places, compacted soil
Blooms: June to September
Flower: Up to 2 mm. No petals. Sepals white and green; somtimes pinkish.
Stems are encircled by papery sheaths (ocrea) at leaf nodes.