Inkweed

Phytolacca octandra L.

Family: Phytolaccaceae

Names:

Phytolacca is derived from the Greek phyton meaning plant and the Neo-Latin lacca meaning lacquer, the gum or resin from some Asian trees is called lac. It alludes to the red dye of the berries.
Octandra refers to the eight sections of the fruit.
Inkweed refers to the red inky juice in the ripe berries.

Other Names:

Red Ink plant, Red Inkweed, Dye Berry, Pokeweed.

Summary

Inkweed is a short lived perennial, woody-based, hairless herb to 2 m high and sometimes tinged with red. The oval leaves are 4-25 cm long. It has several spikes of small greenish white flowers. The flowers have 5 petal-like sepals each 2.5-4 mm long. There are 7-10 stamens and 8 styles. The fruits are reddish black succulent berries and produce red juice (ink) when ripe and crushed. It has a somewhat tuberous taproot and long thick lateral roots.
Native to tropical America, Inkweed is now a weed of roadsides, creek lines, poorly-managed pastures and waste land where it is readily spread by birds. It flowers mainly in spring and summer.
It contains a number of toxic compounds.

Description

Cotyledons:

Two.

Leaves:

Alternate to almost opposite. Green turning red with age.
Stipules -
Petiole - 8-25 mm long. Hairless.
Blade - Green, oval to egg shaped, 40-100(150) x 7-40(130) mm, smooth and soft. Tip pointed. Edges curved, Base tapering. Hairless.

Stems:

Up to 2000 mm tall. Stout, woody at the base, soft near the top. Hairless, smooth, angular, much branched and often reddish purple.

Flower head:

Erect. Dense spikes of many flowers at the ends of branches. 60-120 mm long when in fruit. Flower head stalk 5-15 mm long. Flower stalks up to 3 mm long.

Flowers:

Bisexual. Greenish white turning reddish in fruit. Each with a small bract.
Ovary - style bent back, 0.5 mm long. 8 sections (carpels)
Styles - 8, bent back.
Sepals - 5 almost free petal-like segments. Greenish-white, 2.5-4 mm long. Persistent.
Petals - None.
Stamens - 7-10
Anthers -

Fruit:

Succulent berry. Green then red then shiny, purple- black with red juice. Globular becoming flattened, indented at the top, 6-10 mm diameter. 5-8 lobed with each lobe containing a seed. 5-8 hard seeds.

Seeds:

Black. 2 mm long. Shiny. Hard.

Roots:

Shallow, stout, taproot and spreading laterals.

Key Characters:

Woody based hairless herb to 2 m tall.
Bisexual flowers.
8 celled flattened globular berry with red juice.

Biology

Life cycle:

Short lived perennial surviving 2-3 years. Flowers throughout the year with a peak in August to October.

Physiology:

Reproduction:

Mainly by seed. It will re shoot from the base.

Flowering times:

Flowers throughout the year with a flush in August to October in Perth.
Spring and summer in south west WA.
Mainly November to May in SE Australia.

Seed Biology and Germination:

Has a flush of germination in spring and summer.

Vegetative Propagules:

None.

Hybrids:

Ecology, Population Dynamics and Dispersal:

Birds eat the berries and distribute seed. Grazing stock control young plants.

Origin and History:

Tropical America.

Distribution:

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

Courtesy Australia's Virtual Herbarium.

Habitats:

Often found on rock heaps and wind rows protected from trampling by stock. Common on newly cleared land and wastelands.

Climate:

Temperate.

Soil:

Prefers sandy soils.

Plant Associations:

Blackberry nightshade (Solanum nigrum)

Significance:

Beneficial:

The root was formerly used for medicinal purposes.

Detrimental:

Suspected to be toxic but not usually a problem. Weed of pastures and disturbed areas.

Toxicity:

It contains a number of toxic compounds.
In WA numerous cases of poisoning of horses, cattle, sheep, pigs and dogs have been reported. It is suspected of poisoning cattle, fowls and pigs in eastern Australia but the evidence is circumstantial.
Overseas a few fatal cases of children eating the berries have been recorded.
There is some confusion over the general toxicity.

Symptoms:

Enteritis.

Treatment:

Remove stock from inkweed infested areas.

Legislation:

None.

Management and Control:

Cultivation provides good control. In pastures a heavy railway line or similar can be dragged over them which uproots them and provides partial cheap control. Individual plants can then be removed by cutting through the roots at least 50 mm below ground level to prevent re-sprouting. Spraying the plants with diesel provides good control. Paraquat, and diquat generally provide better control than glyphosate. Hormone herbicides are effective on young plants only.
Burning generally provides little control and the plants re shoot from the base.
Burn or hot mulch garden refuse and don't dump it in or near bushland.
Grazing generally provides reasonable control of isolated small plants but may cause toxicity problems in dense infestations.

Thresholds:

Eradication strategies:

Drag a railway iron or similar across heavy infestations to uproot the plants. Cut the roots about 50 mm below ground level with a mattock to control isolated or remaining plants. Cultivation with discs is also effective.
In open areas, a blanket wiper applying 1 L glyphosate(450g/L) in 2 L water can be used. Single plants may be sprayed with diesel.
Small infestations may be treated with 100 mL Tordon®75-D in 10 L water. This will control existing plants and has residual activity for control of seedlings.
Larger infestations can be controlled with 50 g/ha metsulfuron(600g/kg) or 1 g in 10 L water for hand spraying. Half these rates will control seedlings.
Infestations within 5 km of the target site will need to be controlled to prevent birds spreading seeds. Otherwise, seedlings will need to be controlled annually wherever birds roost. Seedlings may be manually removed but older plants tend to break off and regrow unless cut below ground level with a mattock.

Herbicide resistance:

Biological Control:

Related plants:

Bella Sombra (Phytolacca dioica)
Pidgeonberry or Pokeweed (Phytolacca americana)

Plants of similar appearance:

Blackberry Nightshade (Solanum nigrum).

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P199-200 Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P334.

Blood, K. (2001). Environmental weeds: a field guide for SE Australia. (CH Jerram & Associates, Australia). P91. Photo.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P290.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P579.

Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). P26.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #973.3.

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). P75.

Moore, J.H. and Wheeler, J.R. (2008). Southern Weeds and their Control. (Second Edition). Department of Agriculture and Food Western Australia. P194-195. Photos.

Wheeler, Judy, Marchant, Neville and Lewington, Margaret. (2002). Flora of the South West: Bunbury - Augusta - Denmark. (Western Australian Herbarium, Bentley, Western Australia). P790. Diagram.

Acknowledgments:

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