Century Plant

Agave americana L.

Synonyms -

Family: Asparagaceae (was Agavaceae or Amaryllidaceae)

Names:

Agave comes from the Greek word 'agavos' meaning admirable, referring to the proportions of the plant.
Century Plant refers to its habit of often having long periods between flowering.

Other Names:

Agave
American Aloe

Summary:

A large succulent perennial plant with a large, basal rosette of greyish, fleshy, strap-like, spine-tipped leaves up to 2 metres long with many spines along the edges. The flowering stem is up to 7 m high, candelabra-like, branched and bearing clusters of greenish or yellowish funnel shaped flowers, each about 10 mm in diameter. The fruit is a brown capsule containing numerous seeds. The plant flowers only once and then dies, but spreads by suckering to form quite large areas.
Century Plant is native to Mexico, now a weed persisting around old settlements and flowers in summer and autumn.

Description:

Cotyledons:

One.

First leaves:

Leaves:

Bluish grey to light green. basal rosette of large, spiny, crowded leaves.
Stipules - None
Petiole - None.
Blade - Bluish grey to light green and sometimes with a yellowish margin, succulent, rigid, 1000-2000 mm long x 150-250 mm wide, with spaced spiny, triangular teeth to 5-10 mm long on the edges. Lance shaped. Tip pointed with a terminal spine 30-50 mm long. Sides parallel and spiny toothed. Base not sheathing.

Stems:

The true stem at the base of the leaves is very short.
Flower stem (scape) - 2-7(10) m tall with a 1-3 m long candelabra-like inflorescence. The flower stem is produced rapidly from the centre of the rosette after long periods of vegetative growth. Leafless. Hairless?

Flower head:

Large, terminal candelabra-like inflorescence (panicle) 1-3 m long on a stalk (peduncle) 2-7(10) m tall. Many flowers are in umbellate clusters on the panicle.
Flower stalks (pedicels) 20-40 mm long.
The flower head also produces bulbils.

Flowers:

Yellow, tubular, bisexual, often drooping, 70-100 mm long.
Ovary - Inferior. 3 celled, 30 mm long. Numerous ovules in each cell on axile placentas.
Style - Thread like and shortly 3 branched or stout.
Stigma - 3 lobed.
Perianth - United below to form a tube 10-20 mm long with 6 unequal lobes 20-35 mm long above. Shorter than the stamens.
Stamens - 6 that are 60-100 mm long and inserted at the base of the perianth and longer than the perianth.
Anthers - 2 celled, dehiscing by longitudinal slits.

Fruit:

Oblong capsule, 40-60 mm long and brown at maturity with numerous black seeds.

Seeds:

Black, flattened.

Roots:

Rhizomes.

Key Characters:

Basal rosette of succulent leaves >1 m long with spiny toothed margins and a spinose apex.
Scape >1.5 m.
Inflorescence a panicle.
Flowers yellowish.
Tepals >2 cm long.
Ovary inferior.
6 anthers.
Adapted for J. Black, G. Harden.

Biology:

Life cycle:

Perennial. A flower stem is produced from the centre of the crown of leaves after 5-60 or more years of vegetative growth. Each crown only flowers once then dies and daughter crowns from the rhizome continue the plant.

Physiology:

Very drought tolerant.
Sap may cause skin irritation.

Reproduction:

By suckers and bulbils.

Flowering times:

Usually only flowers every few years.
January and April in WA. January in Perth.
Late summer in SA.
December to February in Victoria.
Summer to Autumn in NSW.

Seed Biology and Germination:

Vegetative Propagules:

Rhizomes and bulbils. The bulbils form in the flower head.

Hybrids:

2 varieties are recognised in WA.

Allelopathy:

Population Dynamics and Dispersal:

Long distance spread by intentional planting. Medium distance spread by dumping of garden refuse. Local spread by shoots from rhizomes, seeds and bulbils.

Origin and History:

Native to Mexico.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Lord Howe Island.
Carnarvon, Coolgardie, Geraldton Sandplain, Swan Coastal Plain, Avon Wheatbelt, Jarrah Forest, Warren, Mallee and Esperance Plains region in WA.
Widely distributed throughout the world.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Cool temperate, warm temperate, Mediterranean.

Soil:

Sand, clay, loam.

Plant Associations:

Significance:

Beneficial:

Ornamental. Hedge plant.

Detrimental:

Environmental weed that may form dense clumps.
Classified as a “Garden Thug”.

Toxicity:

Sap may cause contact dermatitis.

Symptoms:

Skin rash.

Treatment:

Avoid getting sap on the skin and especially on broken skin.

Legislation:

Management and Control:

Difficult to control by hand because of its spiny nature and irritating sap.
Regrows from rhizomes after slashing.

Thresholds:

Eradication strategies:

Remove mechanically ensuring the rhizomes are also removed and burn.
Spray the plant with a mix of 3 L fluroxypyr200 in 100 L diesel or 2 L Access® in 100 L diesel. Apply 1 L mix per 10 square metres of infestation.
Or Drive a crow bar into the centre of plant and pour 10 mL of undiluted fluroxypyr200 or Access® down the crow bar into the wound.
Or Inject the base of the leaves with 5 mL of a mix of 1 g metsulfuron600 in 5 L water (Make a fresh mix each few days or top up an old mix to 5 L and add another gram of metsulfuron).

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Agave sisalana is retted for sisal hemp fibres from the leaves. It naturalised in Rottnest Island in WA and was eradicated.
Some species in this genus are used to make alcoholic drinks.

Plants of similar appearance:

Yucca aloifolia is smaller and has a superior ovary.
Furcraea foetida is smaller and the stamens are shorter than the perianth
Aloe vera is much smaller.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P16.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). Part 1, P366. Diagram.

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Blood, K. (2001). Environmental weeds: a field guide for SE Australia. (CH Jerram & Associates, Australia). P168. Photo.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P190. 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 4. P68. Diagram.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (2007). Western Weeds. A guide to the weeds of Western Australia. (Second Edition). Plant Protection Society of Western Australia, Perth, Western Australia. P4. Photo.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #23.1.

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). P752.

Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P29.

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

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 for more information.