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Agave americana

Perennial herb, up to 8 m, with a rosette of fleshy leaves and yellow-greenish flowers, arranged in a large raceme.

Scientific name: Agave americana L.

Common names: century plant, agave, American agave, American aloe

Family: Agavaceae

Status in Portugal: invasive species (listed in the Decreto-Lei nº 92/2019, 10 july)

Risk Assessment score: 18 | Value obtained according to a protocol adapted from the Australian Weed Risk Assessment (Pheloung et al. 1999), by Morais et al. (2017), according to which values above 13 mean that the species has risk of having invasive behavior in the Portuguese territory | Updated on 30/09/2017.

Last update: 07/07/2021

Family: 
Agavaceae
Appearence: 
Grasses and herbs

How to recognise it

A very robust perennial herb up to 8 m, rhizomatous and sometimes stoloniferous.

Leaves: light green or glaucous, very large (1-2,5 m x 15-30 cm), oblong–lanceolate, fleshy, with a spiny margin and with an apical spine of 3-5 cm, blackened, arranged in a large basal rosette (1-2 x 2-3,7 m).

Flowers: greenish-yellow, large (7-9 cm), arranged in a large panicle (4-8 m), with 20-25  patent branches, inserted in the centre of the leaf rosette.

Fruits: triangular capsules, oblong, with many black seeds inside.

Flowering: it flowers only once, around its 20- 30 years, and dies after forming fruits. The flowering season is normally between May and June.

 

Similar species

Other Agave species are similar, for example, A. ferox K.Koch (of wider leaves – up to 35 cm – and apical spines of 10 cm) and A. atrovirens Karw (with rosettes up to 1,6 m high, and smaller dark green leaves – up to 1 m – and an apical spine up to 12 cm). Several cultivars are frequent, for example, A. americana cv. Marginata, with green leaves and a yellow margin, and A. americana cv. Variegata, with a white stripe on the margin of the leaves.

 

Characteristics that aid invasion

It reproduces vegetatively, from rhizomes, throughout which small rosettes develop that originate new plants.

It also reproduces by seed, having great germination capacity.

Native distribution area

Mexico and western USA.

 

Distribution in Portugal

Mainland Portugal (Beira Litoral, Estremadura, Ribatejo, Alto Alentejo, Baixo Alentejo, Algarve), Azores archipelago (islands of S. Miguel, Graciosa, Faial, Flores), Madeira archipelago (islands of Madeira and Porto Santo).

 

Geographic areas where there are records of Agave americana

Other places where the species is invasive

Mediterranean Basin (from Portugal to Minor Asia), North America (USA), Australia, South Africa, Pacific Islands.

 

Introduction reasons

Ornamental purposes.

 

Preferential invasion environments

Littoral areas and warm and dry areas of the interior. Throughout hedges, valleys, slopes, cliffs, stony, arid and sandy places, roadsides.

Very resistant to drought and high temperatures. It tolerates light frost.

Impacts on ecosystems

The large leaves create shadow that inhibits the development of native vegetation.

 

Economic impacts

High costs in the application of control methodologies.

 

Other impacts

Contact with the leaves may cause allergies.

The spines of the leaves are harmful, and they prevent the presence of animals and make control methodologies applications difficult.

 

Natura 2000 Network habitats more subject to impacts

– Vegetated sea cliffs of the Mediterranean coasts with endemic Limonium spp. (1240);
– Atlantic decalcified fixed dunes (Calluno-Ulicetea) (2150);
– Coastal dunes with Juniperus spp. (2250);
– Thermo-Mediterranean and pre-desert scrub (5330);
– West Mediterranean clifftop phryganas (Astralago-Plantaginetum subulatae) (5410).

Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.

The control methodologies used for Agave americana include:

 

Physical control

Manual/mechanical pulling: preferred methodology for small plants and/or with well-developed rhizomes. When in sandy substrates, pulling is normally easy. However, in more compacted substrates, pulling must be during the rainy season as to facilitate the removal of the root system and/or rhizomes. On cliffs, pulling should be done carefully as to avoid disaggregation of the rocky substrate. As far as possible, it should be guaranteed that there are no large roots or rhizomes left in the ground. Pulling should be done before flowering.

 

Psysical + chemical control

Cut stump method: applied to large plants. Cut the stems close to the ground as much as possible, and later application of herbicide (active substance: glyphosate) to the cut surface. It should be done before the flowering period.

 

Chemical control

Herbicide injection in the stems: applied to large plants. It consists in injecting herbicide (active substance: glyphosate) in the stems. It should be done before the flowering period.

 

Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

Dana ED, Sanz-Elorza M, Vivas S, Sobrino E (2005) Especies vegetales invasoras en Andalucía. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla, 233pp.

 

 

Global invasive">Invasive species">Species Database (2012) Agave americana. Available: http://www.issg.org/database/species/ecology.asp?si=1664&fr=1&sts=&lang=EN [Retrieved 10/11/2012].

 

 

 

 

Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.

 

 

 

 

Osorio VEM, de la Torre WW, Land EO, Silva L, Fernandes FM (2008) Agave americana L. In: Silva L, Land EO, Luengo JLR (eds) Flora e fauna terrestre invasora na Macaronésia. Top 100 nos Açores, Madeira e Canárias. Arena, Ponta Delgada, pp. 209-212.