Knotweeds, Docks & Allies
What are they?
This is a family of potentially rather confusing plants, with most of the groups within the family consisting of a number of rather similar species. This is a large family which has species throughout the world and includes a number of edible species.
Where are they found?
Many species are non-natives that have been introduced into North America from elsewhere, mostly Europe and eastern Asia. As such these tens to be plants of cultivated and disturbed ground, with a number associated with damper ground. Native species are mostly found in moist soil, but a few are typical of dry habitats.
Identification
Many species can be tricky to identify and it is often necessary to take careful note of the flower spike, ocrea and the presence or absence of glandular hairs on the stem. In some species, such as the docks, the shape of the fruiting body is very useful.
One technical term that it is useful to know when identifying this group is Ocrea. The ocrea is a papery, often more or less transparent, sheath which surrounds the stem at the base of each leaf. The presence or absence of bristles on the ocrea can be important for identification.
Sheep's Sorrel Rumex acetosella
Introduced from Europe. A common and often co-dominant species in short grass communities, especially on untreated lawns. Flowers May to July. Most commonly noticed in flower, when patches of golden-brown to red flowers color up Cape May lawns.
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Swamp Dock Rumex verticillatus
Typically found in wet ground along streams in woodland and similar shady places, but also occurs in open wet ground such as at Cape May Point State Park. Flowers June to August.
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Curled Dock Rumex crispus
A common to abundant and sometimes dominant plant of abandoned and waste land, roadsides and other marginal habitats, even coastal dunes. Flowers May to June. Best told by its rather narrow leaves with strongly curled and waved margins. Fruit narrowly heart-shaped, or like a small hand trowel.
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Broad-leaved Dock Rumex obtusifolius
(Bitter Dock) Introduced from Europe and not uncommon as a weed of waste and disturbed places, roadsides and old meadows. Flowers June to July. The large leaves have a heart-shaped base to them; fruits are strongly bristled.
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heart-shaped base |
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Coast Jointweed Polygonum articulatum
A fairly common plant of dry, sandy areas, particularly favoring coastal dunes and dry woodland. Plants often spread out to form eye-catching patches of white flowers in late summer and autumn. Flowers September to October.
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with white dots |
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Japanese Knotweed Reynoutria japonica
A remarkably agressive, alien invasive from eastern Asia. Once popular as a garden plant, this species is rapidly increasing as a coloniser of roadsides, damp woodland, waste places, abandoned gardens and cultivation. Stems can grow to seven feet tall or more, though are often shorter where growing in the shade or on roadsides where it may be cut regularly. Flowers May to July.
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Climbing False Buckwheat Fallopia scandens
A climbing species, usually found clambering over low shrubs and other vegetation in a wide range of habitats. Flowers late July to September.
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Black Bindweed Fallopia convolvulus
Introduced from Europe. An occasional weed of disturbed ground in gardens, roadsides and waste places. A twining species, but more often seen trailing over the ground. Flowers late July to September.
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Prolific Knotgrass Polygonum prolificum
Scattered here and there in coastal areas, often in grassy swards and roadsides near saltmarshes. Flowers July to October. A slender, upright species with leaves that have rather parallel sides.
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Equal-leaved Knotgrass Polygonum arenastrum
Introduced from Europe. Common and widespread. Flowers July to October. A rather variable species, but typically found growing as a weed of lawns and other short-grass areas. A small, low-growing species, but grows more upright when among taller vegetation.
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pink-tinged |
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Small's Knotgrass Polygonum buxiforme
Widespread but local in sandy soils, mostly along ther coast but occasionally inland too. Flowers July to September.
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Common Buckwheat Fagopyrum esculentum
Occasionally found as a weed of arable and waste places and often in gardens where it originates from bird seed. Flowers June to September.
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Virginia Knotweed Persicaria virginiana
(Jumpseed) An understorey plant of loamy woodland soils. Flowers July to September. The thin, 'rat-tail' spikes of small, white flowers topping clumps of broad leaves are quite distinctive.
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Asiatic Tearthumb Persicaria perfoliata
(Mile-a-minute Vine) A highly invasive alien species that is threatening native habitats in a number of northeastern US states. As yet it is a recent colonist in New Jersey and there are no published records for Cape May County, but the photos here were taken at Cape May Point State Park in 2010. The prickly stems, triangular leaves and blue berries are diagnostic. Flowers July to September.
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hooked spines |
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Halberd-leaved Tearthumb Persicaria arifolia
Frequent in swamps and marshes, both fresh and brackish and especially where the water is tidal. A straggly plant that clambers through tall vegetation, using its hooked spines to aid climbing. Leaves distinctive, shaped like spearheads. Flowers August to October.
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hooked spines |
Arrow-leaved Tearthumb Persicaria sagittata
Occasional in swamps and marshes, both fresh and brackish. A straggly plant that clambers through other vegetation, using its hooked spines to aid climbing. Leaves lobed at the base. Flowers August to October.
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Swamp Smartweed Persicaria amphibia
A scarce plant of wet or damp ground. Flowers August to September. This species currently includes a rather odd-ball mix of forms which have variously been split as species in the past. The form included here (variety emersum) is a terrestrial form which may grow to a meter or more high and can colonize large areas. It was previously considered a separate species, Persicaria coccinea. Plants large and robust with leaves that are hairy below.
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Dense-flowered Smartweed Persicaria glabra
Scattered here and there in wet places in the lower part of the peninsula, often growing out onto the water surface from the margins of ponds. Flowers August to September. A rather large and often sprawling species with pink or white flowers and smooth, unfringed ocrea.
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Mild Water-pepper Persicaria hydropiperoides
Common and widespread on the margins of wetlands and in disturbed, damp soil. Flowers July to September.
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Dotted Smartweed Persicaria punctata
Widespread and frequent in wet soils and seasonally flooded ground. Flowers July to October.
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on surface |
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Pennsylvania Smartweed Persicaria pensylvanica
Common species of wetlands on richer, loamy soils. Widespread in suitable locations. Flowers June to October.
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has stalked glands |
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Pale Persicaria Persicaria lapathifolia
Introduced from Europe and now widespread in damp ground and as a weed of cultivation in richer soils. Flowers July to October.
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| long and curved |
below flower spike |
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Introduced from eastern Asia. Much confused in books in the past, this species was introduced to North America near Philadelphia in 1910 and has since spread quite extensively. There are currently no published records for Cape May County, but it appears to be frequent here, at least in the south of the county. Flowers June to October.
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flower head |
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(Lady's-thumb) Introduced from Europe. A variable species which may have white or (more usually) pink flowers and usually has a dark blotch on each leaf. Originally a wetland plant but readily colonises waste ground, cultivated fields and other disturbed areas. Flowers July to October.
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black blotch |
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