Pampas Grass

Cortaderia selloana (Schultes &Schultes f.) Asch. & Graebner

Synonyms - Arundo selloana, Cortaderia argentea, Gynerium argenteum.

Family: Poaceae.

Names:

Cortaderia is from the Spanish word for cutting and refers to the very sharp leaf edges.
Selloana celebrates the German naturalist Friedrich Sellow (1789-1831).
Pampas grass refers to its place of origin on the pampas of South America.

Other names:

Common Pampas Grass
Silwergras (South Africa).

Summary:

Pampas Grass is a large, rhizomatous, perennial tussock grass up to 2 m wide and has tall plume-like spikes to 2-4 m high. The leaves are long, arching, and sharp edged with most of the tips held above the ground. The large, feathery, silver to cream-coloured inflorescence to 1 m long is sometimes tinged with purple and much-branched and held high above the leaves on an unbranched, smooth stem. The leaves have very sharp margins and rough ribs. There are separate female and hermaphrodite plants. The latter are often functionally male but occasionally set seed. The inflorescence of the hermaphrodite plant is hairless and that of the female plant is silky-hairy when viewed under a hand lens. The spikelets each have 2-5 florets, the outer segment of each floret (lemma) tapering into a slender apical bristle or awn.
Native to South America, it is a garden escape and now a common weed of wetlands, particularly around Albany. It flowers in winter.
Every effort should be made to control this plant because of the explosion in spread as seed production increases with the movement of hermaphrodite plants into the basically female Australian populations. Each seed head or plume can produce up to 100,000 seeds.

Description:

Forms dense clumps several metres wide.

Cotyledons:

One

Leaves:

Tufted and crowded at the base of stems. Blue green on top, darker green underneath.
Blade - Long and narrow, striped, tapering to a fine point. 800-2000 mm long x 5-35 mm wide. Arching away from the sheath (rather than drooping from the sheath) with most leaf tips held above the ground. Hairless or minutely hairy. Rough to touch. Edges are knife sharp and finely serrated. Obvious midrib, no secondary veins. Folded in the bud.
Ligule - Tufted rim of hairs, 2-3 mm long.
Sheath - Smooth, slightly hairy, no waxy bloom and no distinct midrib. Hangs down in a spiral when dead.

Stems:

Flower stem - Grey green to yellow green, erect, hollow, 2000-6000 mm tall, up to 30 mm diameter.

Flower head:

Plants are usually dioecious or gynodioecious. Thus there are female and hermaphrodite (bisexual) plants.
Silver white to pink or mauve, terminal, plume like, feathery panicle, 300-1000 mm long, barely exerted above the basal leaves. The male panicle is hairless and the female panicle is silky hairy. Hermaphrodites tend to be pinker. Seed structures break off where they join the main stem. (Rachilla disarticulating near the base of the internodes forming a stalk 0.5 mm long to the floret) Upper part of rachilla hairy and lower part hairless.

Flowers:

Spikelets - Single, 15-18 mm long. 2-6 flowered. Males are hairless and have a small but sometimes functioning ovary, females are have long silky hairs.
Florets - Female ones silky with close pressed, fine, straight hairs. Bisexual ones are hairless.
Glumes - White, longer than lemma, 9-15 mm long, papery, 1 ribbed, slender. Narrow and tapering to a fine point and short awn. Awn inserted between 2 tiny teeth. Hairless. Lower glume13-15 mm long, upper glume 9-12 mm long
Palea - 3.5-4 mm long in females and about 5 mm long in males
Lemma - Several, 1 ribbed. Soft. Tapering to a deciduous, slender awn about 1 mm long. Male ones 9-12 mm long and hairless. female ones 13-15 mm long and hairy.
Stamens -
Anthers -

Fruit:

Seeds:

Pale straw colour. Narrowly oval, 2 mm long, 0.6 mm wide. Enclosed by glumes. Up to 100,000 seeds produced per plume.

Roots:

Mass of fibrous roots to 4000 mm wide and deep. Arises from short stocky rhizomes. The root system has been calculated to occupy over 100 m-3 of soil on large plants.

Key Characters:

Plants dioecious or gynodioecious i.e. female or hermaphrodite (which are males with a small but sometimes functional ovary).
Height in flower up to 6 m.
Leaves long and crowded at the base of the culms
Leaf blades dull green, somewhat folded near the base, erect and arching away from the stem with most leaf tips above the ground.
Leaf blade midrib channelled on the upper surface.
Leaf sheath glabrous or sparsely hairy.
Culms glabrous or sparsely hairy.
Flower heads emerge mid March to late May (in Victoria)
Flower heads white, cream or purplish, large, plume like and only shortly exerted above the tuft of basal leaves.
Rachilla joints have long silky hairs that envelop the lemma.
Lemma of female spikelet covered with silky hairs.
Ovary not enlarged at the beginning of anthesis.
Adapted from Bill Parsons and S.W.L. Jacobs.

Biology:

Life cycle:

Perennial. Seed germinates in spring and slowly produces a few tillers and short rhizomes in the first year. They very rarely flower in their first season. They become semi dormant over winter and resume active growth in spring. Some may flower in their second year but most take a number of years before flowering, especially on drier sites. Floral initiation occurs in spring but heads don't emerge until late summer. Hermaphrodite plants produce flowering heads a week or so before similar female plants. The main flowering occurs between March and May with occasional ones to September. Hermaphrodite plants rarely produce seed and act as functional males providing pollen to fertilise female plants. Seed may be carried 25 km by wind. New tillers arise from rhizomes on the edge of the mother plant to increase her size. Rhizome fragments readily regenerate and are a major source of spread together with intentional planting. Spread by seed is likely to become the major method of dispersal as hermaphrodites establish in the Australian populations.

Physiology:

Seedlings are frost sensitive.

Reproduction:

By seed and vegetatively.

Flowering times:

June and September in Perth.
February to September in WA.
February to September.
Summer to Autumn in NSW.

Seed Biology and Germination:

Female plants can produce 100,000 seeds per flowering stem.

Vegetative Propagules:

Rhizomes.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

The seed bearing florets are very hairy and readily spread by wind for up to 25 km. Vegetative spread is also common with severed rhizomes establishing readily at suitable sites. Within a site, individual plants increase in size annually by producing peripheral rhizomes. Spread by the nursery trade has almost stopped since the weediness has been publicised but it is still commonly transferred between gardens and the plume like flower heads are often seen in dried flower arrangements. It is rapidly invading disturbed areas and to a lesser extent undisturbed bushland areas.

Origin and History:

South America. Brazil, Argentina, Uruguay and Chile.
Introduced to Australia in the late 1800's as an ornamental garden plant. In most cases the only the female plant was introduced because it has fluffier and more attractive plumes. However, in recent years the hermaphrodite plants have become established allowing viable seed to be set and spread.

Distribution:

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

Courtesy Australia's Virtual Herbarium.

Habitats:

Thrives in both dry and very wet areas, especially on water courses, seepage areas and swamps.

Climate:

Open sub-humid to semi-arid sub-tropical regions.

Soil:

Damp soils.

Plant Associations:

Open areas.

Significance:

Pampas grass has been in many areas for many years with little or so indication of its weed potential. However, the introduction of hermaphrodite plants into many Australian populations means that seed is now being produced and it is expected that Pampas will become a serious environmental weed in many areas. Removal of garden specimens should be encouraged whenever possible to reduce the number of potential sources of seed.

Beneficial:

Previously used for stock feed, shelter and erosion control. It is an ornamental that has become a weed with the introduction of hermaphrodite varieties that cross with ornamental plants to produce seed.

Detrimental:

A serious weed of pine plantations in New Zealand and an environmental weed of the USA and Australia.
An increasingly serious weed of urban bush lands and recreational areas.
Weed of stream banks, wet areas, railways, roadsides, walk tracks and disturbed areas.
It poses a serious fire hazard.
Normal grazing and cultivation controls young Pampas Grass so it is unlikely to become a widespread weed of pastures or agriculture.
It rapidly establishes on bare soil, disturbed coastal forests and wetlands.
Once established it tends to exclude most other species and forms impenetrable clumps.

Toxicity:

Not recorded as toxic.

Legislation:

Noxious weed of NSW, Tas, and WA.

Management and Control:

Mechanical removal is effective, and a backhoe is preferred for larger plants. Seedlings can be uprooted with a garden fork but even small plants can be very difficult to remove by hand. It usually re grows where it is dumped unless it is burnt or buried more than 1 metre deep. Burning followed by repeatedly spraying of the regrowth with glyphosate is effective. Every effort should be made to control this plant because of the likely explosion in spread as seed production increases with the movement of hermaphrodites into the basically female Australian populations.
Seedlings are sensitive to frost, grazing and cultivation.

Thresholds:

It is very invasive especially in disturbed or burnt wet areas. Once established it precludes most other vegetation.

Eradication strategies:

Single large plants can be removed with a backhoe and burnt or buried more than 1 m deep.
Spray until just wet with a mixture of 1 litre of glyphosate (450 g/l) plus 250 mL Pulse® Penetrant in 100 litres of water. Burn when dry. Treat regrowth each spring.
Cut and burn flower heads as soon as they appear in areas where herbicides can't be used and burn and remove parent plants, taking care to remove all rhizome fragments.
The hermaphrodite plants produce plumes a week or two before females. Cut these immediately.
Graze infested areas if possible or replant to native tree and shrub species in bushland areas.
Plants less than one year old may be controlled by hand spraying until just wet with a mixture of 5 mL of Verdict®520 plus 100 mL spray oil in 10 L water. This mix will cause little damage to most native broad-leaved plants.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Pink Pampas grass (Cortaderia jubata) has darker or more purplish plumes and longer flowering stems that are twice as high as the foliage.
Toe Toe (Cortaderia richardii)

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). P43. Photo.

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 4. P565. Diagram.

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). #357.3.

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). P948.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P100-103. Photos.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn) P85. Photo.

Acknowledgments:

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