Creeping Knotweed

Persicaria prostrata (R.Br.) Sojak

Synonyms - Polygonum prostratum.

Family: Polygonaceae.

Names:

Polygonum is from the Greek polys meaning many and gony meaning knee and refers to the many nodes on the stems.
Creeping Knotweed

Other names:

Trailing knotweed

Summary:

A low lying, glandular hairy perennial with oval leaves and membranous sheaths at the base of the petiole with leafy outgrowths and lens shaped seeds.

Description:

Cotyledons:

Two.

Leaves:

Stipules - Brown, opaque, membranous sheaths at base of the petiole often with leafy outgrowths and scattered, spreading, non glandular hairs and short glandular hairs. Edges with tiny hairs or short glandular hairs.
Petiole - Short.
Blade - Lance shaped to narrowly oval, 5-80 mm long x 5-20 mm wide. Hairy with long spreading non glandular and short glandular hairs on both surfaces especially on the veins of the lower surface. Edges sometimes with spreading hairs only.

Stems:

Slender, low lying, climbing or bent upwards at the ends, woody, few branches. Forms roots at lower nodes. Hairy with low lying hairs, non glandular hairs and short glandular hairs.

Flower head:

2-4 flowers in a dense, spike like racemes or panicle, 10-25 mm long, on short stalks(peduncles), emerging mainly from upper leaf axils or at the ends of branches.

Flowers:

Green to pinkish or brown. 3 mm.
Bracts - Brown, egg shaped at the base of the raceme and hairy with scattered spreading hairs and short glandular hairs.
Ovary - 2 styles joined for 2/3 of their length. 2 style branches. 2 stigmas.
Perianth - Tubular, green to pinkish or brown, 3 mm long overall with lobes about twice as long as the tube.
'Petals' - Green to pinkish or brown, 2 mm long
Stamens - 5-6.
Anthers -

Fruit:

Lens shaped, reddish brown to black, shining or dull, triangular pyramidal nut, 1.5-2.5 mm long, with lines of dots and enclosed by the old flower parts.

Seeds:

Enclosed in fruit.

Roots:

Taproot and from stem nodes.

Key Characters:

Flowers in spike like racemes.
Stems prostrate, root at the lower nodes.
Leaves lanceolate or elliptic.
Stipular sheaths, brown, opaque, commonly with a leafy outgrowth.
Spikes like raceme short, 15-25 mm long on short peduncles.
Floral whorl green or pinkish or brown, without glands.
Glandular hairs usually present on the leaves, stems, ochrea and ochreola.
Nut lenticular.
Hirsute perennial.

Biology:

Life cycle:

Perennial. Growth mainly occurs in the warmer months and it may form mats 1000 mm or more wide.

Physiology:

Reproduction:

By seed.

Flowering times:

Summer in western NSW.
Summer in SA.
October to July in Perth.

Seed Biology and Germination:

Vegetative Propagules:

Stem fragments.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread by seed and stem fragments.

Origin and History:

Australia.

Distribution:

ACT, NSW, NT, QLD, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Creeks and lower valley slopes.

Climate:

Temperate.

Soil:

Plant Associations:

Riverine.

Significance:

Beneficial:

Detrimental:

Weed of crops, pastures and wet areas.
Not grazed readily.

Toxicity:

Not recorded as toxic, but suspected to cause illness in stock.

Legislation:

None.

Management and Control:

Thresholds:

Eradication strategies:

Cultivate before flowering.
Glyphosate, dicamba and sulfonyl urea herbicides provide good control.

Herbicide resistance:

Biological Control:

None introduced because it is an Australian native plant.

Related plants:

Black Bindweed (Polygonum convolvulus)
Pale Knotweed (Polygonum lapathifolium, Polygonum lanigerum)
Princes Feather (Polygonum orientale)
Sand Wireweed (Polygonum arenastrum)
Slender Knotweed (Polygonum salicifolium, Polygonum decipiens)
Small Knotweed (Polygonum plebeium)
Spotted Knotweed (Polygonum strigosum)
Tree Hogweed (Polygonum patulum)
Vietnamese mint (Polygonum odoratum)
Water Pepper (Polygonum hydropiper)
Wireweed (Polygonum aviculare)
Polygonum capitatum
Polygonum glabrum

Plants of similar appearance:

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P204.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P283.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P154.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P233. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1002.15.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P114.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.