Pokeweed

Phytolacca americana L.

Synonyms - Phytolacca decandra L.

Family: Phytolaccaceae

Names:

Phytolacca is derived from the Greek phyton meaning plant and the Neo-Latin lacca meaning lacquer as the gum or resin from some Asian trees is called lac or it is from the lac insect that produces a black dye. It alludes to the red dye of the berries.
Americana refers to it origin in America.
Pokeweed is derived from poke which is the Native American word for blood and refers to the red dye that can be made from the fruit.

Other Names:

American Pokeweed
Chuíxù shânglù (Chinese medicine name)
Ink berry
Pidgeonberry
Polk salad
Poke root
Poke salad
Poke sallet
Pokeberry
Redweed
Red ink plant
Virginia poke

Summary

Pokeweed is an erect, hairless, perennial sub shrub, 1-3 m tall that is often woody at the base with a large rootstock. The oval, entire leaves are alternate on long (often reddish) petiolesThe stems and flowers are green to pink to reddish. It has a thick, white fleshy taproot.
The fruits are reddish black succulent berries and produce red juice (ink) when ripe and crushed.
Native to tropical America, Pokeweed has been found in WA where it is spread by birds. It flowers mainly in spring and summer.
It contains a number of toxic compounds.

Description

Cotyledons:

Two.

First leaves:

Leaves:

Alternate to almost opposite. Green turning red with age. They tend to have an unpleasant odour.
Stipules - None
Petiole - usually 10-60 mm long. Hairless.
Blade - Green, oval to lance shaped, 40-300 x 10-120 mm, smooth and soft. Tip pointed. Edges curved and smooth, Base tapering to obtuse. 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.
The stems have a chambered pith.
Flower stem - 40-50 mm long.

Flower head:

Erect. Mostly axillary, open spike like racemes of many flowers. 50-300 mm long when in fruit. Flower stalk (peduncle) 40-50 mm long. Flower stalks (pedicels) up to 5-15 mm long and longer than the fruit.

Flowers:

About 5 mm wide. Bisexual. Greenish white turning reddish in fruit. Each with a small bract.
Ovary - style bent back, 0.5 mm long. 10-11 sections (carpels). Carpels united or occasionally free at the apices.
Styles - 10-11, free.
Sepals - 5 almost free petal-like segments. Greenish-white, 2-4 mm long and wide. Persistent.
Petals - None.
Stamens - Upright, usually 10, generally inserted below the disc in a single whorl. Filaments ~2 mm long.
Anthers - 0.8 mm long.

Fruit:

Succulent berry. Green then red then shiny, purple- black with red juice. Globular becoming flattened, indented at the top, 6-10 mm diameter. Up to 11 lobed with each lobe containing a seed. 7-11 hard seeds.

Seeds:

Black. <2 mm long. Shiny. Hard.

Roots:

Deep, stout, white taproot with a tan cortex and spreading laterals.
The root has concentric rings when cut. The rootstock can be very large and more than 20 cm diameter and over 20 kg.

Key Characters:

Bisexual flowers.
Perianth with 5 sepal
Fruit succulent with 10 carpels
Pedicels in fruiting stage 5-10 mm long, longer that the fruit.
Fruit 6-10 mm diameter.
Stalks of inflorescence 40-50 mm long.

Key to get Phytolacca
Leaves not cordate at the base; ovary superior
Ovary of 5-16 carpels and seeds
Sepals sub equal and not fleshy; carpels (at least in the neotropical species) united
Ovary sessile, gynophore absent


Phytolacca species key
Bushy herb or subshrub up to 2 m. Leaf laminas narrowly elliptic to elliptic-lanceolate. Flowers hermaphrodite. Sepals spreading at anthesis. Carpels completely fused. Fruit 7-8 (9) lobed, style remains clustered inside depression at apex of fruit, black when ripe
Phytolacca octandra
OR
Inkweed (Phytolacca octandra) flowers are borne on very short stalks (i.e. pedicels) only 2-3 mm long and usually have 7-8 stamens. Their 'petals' (i.e. tepals or perianth segments) turn red and persist on the developing fruit. The mature fruit are relatively small (4-6 mm across) and usually have eight slight lobes (i.e. they usually contain eight seeds).
versus
American pokeweed (Phytolacca americana) flowers are borne on relatively long stalks (i.e. pedicels) 5-10 mm long and usually have 10-11 stamens. Their 'petals' (i.e. tepals or perianth segments) turn red and persist on the developing fruit. The mature fruit are relatively large (5-11 mm across) and have ten or eleven slight lobes (i.e. they contain ten or eleven seeds).
versus
Venezuelan pokeweed (Phytolacca rivinoides) flowers are borne on relatively long stalks (i.e. pedicels) 7-12 mm long and have 9-14 stamens. Their 'petals' (i.e. tepals or perianth segments) fall off as the fruit begin to mature. The mature fruit are relatively small (5-6 mm across) and have 12-16 slight lobes (i.e. they contain 12-16 seeds).
See Palynotaxomic study of the Phytolaccaceae (Nowicke, 1968)

Biology

Life cycle:

Short lived perennial. Tends to die back to the rootstock over winter.

Physiology:

Tolerates Mn (Zhang, Huang, Zhang, Li and Chai, 2009).
Phytolacca americana leaf possesses adequate molluscicidal (snail killing) activity and a significant acute toxicity to the zebra fish (Fang et al., 2011), (Aldea and Allen-Gil, 2005).

Reproduction:

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

Flowering times:

Spring and summer in south west WA and NSW.

Seed Biology and Germination:

The seeds have a long viability in the soil. (one website suggests they last 40 years https://gardeningknowhow.com)
The proportion of seeds germinating after passage through avian frugivores was greater than control seeds (0.88 vs. 0.67, respectively) and they germinated more quickly but the total number of viable seeds was not changed by passage through the birds gut (Orrock, 2011).
Has a flush of germination in spring and summer.

Vegetative Propagules:

Rootstock.

Hybrids:

Allelopathy:

P. americana leaf extract inhibited seed germination, seedling growth, and biomass of Cassia mimosoides when compared to controls. However, root and shoot growth in soil from infested areas was stimulated relative to control soil
(Kim et al., 2005)

Ecology, Population Dynamics and Dispersal:

Birds eat the berries and distribute seed (Orrock, 2011).
Foxes probably eat berries and spread seed.
Spread by water flows, road works and dumping of garden waste.
During the first year after the hardwood clear-cut, seed production was dominated by the ruderal Phytolacca americana (Diaz-Toribio and Putz, 2017).
Grazing stock control young plants.

Origin and History:

North and tropical America.
Found in WA in 2018 and is under an eradication program.

Distribution:

NSW, QLD, SA, WA, NZ

Courtesy Australia's Virtual Herbarium.

Habitats:

Common on newly cleared land and wastelands.

Climate:

Temperate.

Soil:

Prefers sandy soils.

Plant Associations:

Blackberry nightshade (Solanum nigrum)

Significance:

Beneficial:

The root and other parts was formerly used for medicinal purposes.
Medicinal uses include production of pokeweed antiviral protein (PAP) extracted from leaves as a potent immunotoxin against leukaemia and lymphoma cells (Myers et al., 1991).
Extracts have anti-viral activity (D'Cruz et al., 2004).
May be useful for phytoremediation of heavy metal contaminated sites (Zhang et al., 2009).
Prevents bean-beetle and worm infestations in garden plants (Pence, 1987).
Extracts have action on ovarian cancer cells (Wang et al., 2008).
The seeds and fruit of Phytolacca americana are molluscicidal (kills snails) and are not mutagenic (Pezzuto et al., 1984).
Food for birds. Food for the red fox but generally toxic to other mammals.
Ornamental and some cultivars have more showy clusters of fruit.
Berries can produce a toxic dye.
Toxic to zebra mussels.
Used as a wine colouring in the 1800's.

Detrimental:

Maybe toxic but not usually a problem for stock
Weed of pastures and disturbed areas.
Alternate host for fruit fly Drosophila suzukii (Lee et al., 2015).

Toxicity:

All parts of the plant are toxic. The roots are most toxic followed by leaves, stems, green fruit then ripe fruit.
It contains a number of toxic compounds.
There is some confusion over the general toxicity.
Contact with the bare skin should be avoided.

Symptoms:

Enteritis, emesis, catharsis, respiratory paralysis.
Emetic, vomiting, spasms, convulsions, bloody diarrhoea.
Vomiting usually starts about 2 hours after consumption.
Sap may cause dermatitis in some people.

Treatment:

Remove stock from infested areas.
Recovery normally takes 1-2 days.

Legislation:

Declared weed and under an eradication program in WA.

Management and Control:

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.
Hot burns but not cool burns facilitated germination of Phytolacca americana (Glasgow and Matlack, 2007).
More Phytolacca americana germinated after fire (Schuler and Leichty, 2008).
Mowing rapidly decreased the growth of P. americana but it recovered in the next year (Fu et al., 2012).
1/3 root cutting reduced the growth in the first year but it recovered by the third year. 2/3 root cutting and whole cutting provided good long term control (Fu et al., 2012). Paraquat only killed the aboveground parts of P. americana but it recovered the following year (Fu et al., 2012).
100 mL glyphosate450 per L water (~ 100 L glyphosate450/ha) provided good long term control (Fu et al., 2012).
Avoid disturbance as it tends to establish in forest gaps (Luken et al., 1997).
Glyphosate provided 79 to 91% control in glyphosate tolerant soybean (Patches et al., 2017).
2,4-D, dicamba, and mesotrione plus atrazine provided at least 80% control in corn (Patches et al., 2017).
(DiTomaso et al., 2013) have foliar treatments of 2,4-D + fluroxypyr (2% + 2%), dicamba and glyphosate as effective on small plants. Imazapyr is variable. Triclopyr 1:20 in oil as basal bark or overall drizzle treatment and requires downward translocation for large plants which occurs late in the season.

Thresholds:

Eradication strategies:

Small infestations may be treated with 100 mL Grazon® in 10 L water. This will control existing plants and has residual activity for control of seedlings. Hexazinone can be used for control in pine plantations.
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.
Single plant may be controlled wit a basal bark spray of 1L triclopyr in 50 L diesel.
Large plants may be controlled by drilling a 20 mm hole about 100 mm deep into the rootstock and putting 10 mL triclopyr600 into the hole.
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.

Herbicide resistance:

None reported

Biological Control:

Related plants:

Pokeweed (Phytolacca americana) has 7-11 seeds in each fruit, usually one staminal whorl, inflorescence is an open raceme, carpels united.
Bella sombra (Phytolacca dioica) occurs in QLD, NSW and Victoria. It has male or female flowers and the carpels are free at the apices.
Inkweed (Phytolacca octandra) has more oval leaves and a more compact inflorescence (flower head). Pedicels in fruiting stage 0-3 mm long and shorter than the fruit. Fruit 4-6 mm diameter. Stalks of inflorescence 10-20 mm long.
Phytolacca purpurascens is found in Melbourne.
Phytolacca clavigera is in New Zealand and not recorded in Australia. It may be a horticultural form of P. acinosa. It has completely free carpels.
Phytolacca rivinoides occurs in northern Queensland. 10-16 seeds in each fruit and it usually has 2 staminal whorls.
Phytolacca dodecandra (Not in Australia - different to P. decandra) Scrambling herb or shrub up to 13 (20) m. Leaf laminas ovate to elliptic. Flowers usually functionally unisexual. Sepals reflexed at anthesis. Upper part of carpels free. Fruit 4-5 (8) lobed, style remains pointing outwards at apex of each carpel, orange to red when ripe

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). P200.

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

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

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 1. P176. Diagram.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). 781.1.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.



Acknowledgments:

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