Century plant (Agave americana)

Datasheet

Description

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Century plant (Agave americana), in bloom

Century plant (Agave americana), flowers

Common names

Century plant, American agave, American aloe [English]; agave américain, agave d'Amérique [French]; choka bleu [French / Réunion]; agave amarillo, pita, maguey [Spanish]; hundert-jährige Agave [German]; honderdjarige aloë [Nederlans]; piteira [Portuguese]; alivera, garingboom [Afrikaans]; أغاف أمريكي [Arabic]; 黃边龙舌兰 [Chinese]

It is important to note that the vernacular names used for plants of the Agave genus are common to different species and do not strictly correspond to specific taxons. The spanish word "maguey", notably, is use for all Agave species.

Species

Agave americana L. [Agavaceae]

Synonyms

Agave rasconensis Trel. ex Standl., Agave zonata Trel.

Related feed(s)

Description

The century plant (Agave americana L.) is a perennial succulent herb, up to 10 m tall when flowering. It is native to Mexico and to the Southern USA, and its has been introduced in all warm areas around the world as an ornemental. Like other agaves, Agave americana has long been used by the populations of Central and South America for a large variety of purposes, including handicrafts, food, ethnomedicine and livestock feeding.

Morphology

Agave americana is a polymorphic species, with many subspecies and varieties, and it hybridates with other Agave species such as Agave salmania (Gentry, 1982). The plant forms a massive rosette of 20-40 succulent leaves, growing from a short and thick stem close to the ground. The rosette can be as wide as 5 m in diameter. The leaves are 15-25 cm wide and 1-2 m long, smooth and tough, nearly rigid, with a deep gutter that often causes them to recurve at the tip. They have serrated edges, and straight or curved thorns, and a large, sharp apical thorn. The leaf margin is undulate with dark brown teeth that turn grey with age. The leaves of cultivated forms are often grey to grey-blue with horizontal stripes on the back, but there are dark green forms and variegated ones with numerous and inconstant colour patterns (yellow or white stripes, pink edges etc.). The inflorescence is a candelabra-like panicle that can reach up to 10 meters. It has 15-35 branches with dense clusters of green-yellow flowers on the upper half to third of the stalk. Agave americana is rhizomatous and freely produces basal shoots (suckers) (Gentry, 1982; Irish, 2000; Oudhia, 2007).

Uses

Agave americana is a multipurpose plant. Its most popular use worldwide is ornamental. Agave comes from the greek αγαυή, which means "noble" or "admirable". Due to its robustness and spectacular appearance, the century plant is planted in gardens and roadsides in temperate and warm regions all over the world. In Central and South America, Agave americana is suited for a large variety of utilisations. The sap is used in numerous drink and food preparations: alcoholic beverages, sweeteners, fortifier, leavening, and to prepare syrup, panela, vinegar, ice cream, bread, tortillas, barbecues etc. The leaves, plant heart, floral stalk and roots are used as material for handicrafts (furniture, drums, fibre for clothes, footwear, ropes etc.), for construction (mixed in mudbricks), and for fuel. They are used in South America and Southern Africa to feed livestock, though the presence of antinutritional substances (saponines and oxalates) limits this latter use (see Potential constraints). Agave americana is planted as live fence to delimit land for grazing and farming, and for erosion control (see Environmental impact) (GISD, 2020; Irish, 2000; Oudhia, 2007; de la Torre et al., 2018).

Agave americana, particularly its sap, is widely used in human and veterinary ethnomedicine (Oudhia, 2007). Several compounds identified in the leaves have antibacterial, antifugal, molluscicidal or insecticidal properties (Santos-Zea et al., 2012; Condor Quispe, 2018; Oudhia, 2007). The leaves contain angiotensin-converting enzymes that can be used to treat hypertension, and sapogenins that can be used in the manufacture of semisynthetic corticosteroids (Oudhia, 2007).

Distribution

Agave americana is believed to have originated from the arid and semi-arid subtropical climates of North-Eastern Mexico, where the subspecies protoamericana can be found (Gentry, 1982). Like other agave species, it was domesticated 10,000 years ago, and has been used since as a source of fibre, food and beverage throughout Central and South America. It was later introduced by the Europeans to other countries (de la Torre et al., 2018). Agave americana is now widely scattered around the world and can be found in all continents except Antarctica. It has become naturalized and even feral in all the warm regions from California to Florida, throughout the warm Mediterranean areas of Europe and northern Africa, in southern Africa, India, and Australia (Oudhia, 2007; Irish, 2000). A hardy species, Agave americana can grow in a wide range of conditions, including cliffs, urban areas, woodlands, grasslands, riparian zones, beaches and sandy areas, and rocky slopes (GISD, 2020).

In its native range, Agave americana grows in areas where rainfall ranges from 250 to 800 mm with a well-defined spring season. Temperatures are high during late spring and summer, while frosts are common during winter and are severe in the higher elevations in the North (Gentry, 1982). Its countless varieties are now adapted to a wide range of climatic and soil conditions (Oudhia, 2007). A highly forgiving species, Agave americana grows in hot areas of limited rainfall, such as southern Arizona, or in areas of cooler temperatures, such as the Mediterranean coastal climates, where it grows well provided it receives some water in summer (Gentry, 1982; Irish, 2000). In East Africa, Agave americana grows from sea-level to 2500 m altitude, and is found in both low and high rainfall areas (Oudhia, 2007). Generally, the species is xerophytic and tolerates protracted droughts. It fixes CO₂at night and synthetizes with closed stomatas in daytime, which minimizes water loss in leaf tissue (Oudhia, 2007; Gentry, 1982). Agave americana varieties have some frost resistance in southern temperate climates, tolerating temperatures down to -9°C and perhaps lower (Gentry, 1982; Irish, 2000). Agave americana is tolerant of wind, salt, high temperatures, and extreme drought. It can grow in shallow, very dry, low fertility soil and can colonize bare sand. It exhibits broad tolerance to different soil types (GISD, 2020; Gentry, 1982).

Forage management

Agave americana is a monocarpic species and thus dies after fruiting. It blooms only once, after about 10 years in warm climates, or up to 35 years or more in cool climates, hence its name of "century plant" (GISD, 2020; Irish, 2000). In its native range, the plant blooms from June to August (Irish, 2000).

Establishment

Agave americana can multiply through different methods. It can reproduce through it seeds, which have a high germination rate (GISD, 2020). However, the usual method is by plant and stolon (suckers) fragments (GISD, 2020). Two year-old suckers or seedlings are used to establish it. The plants are planted in furrows 3 to 5 m apart and 1 to 2 m apart in the furrows. It is recommended to plant it on the periphery or alongside fences (De Kock, 1980). The plant can also multiply via rhizomes. Bulbils are produced in the floral stems, which can also give rise to daughter plants (GISD, 2020).

Yield and processing

Leaves are usually harvested from 4 to 6 year-old plants. A yield of 120 t/ha of leaves can be expected annually and that on relatively poor soils. Trials in South Africa have shown that harvesting Agave americana for fodder was labour-intensive (King et al., 2011). The leaves need to be prepared to make them usable for fodder. They must be chopped against the stem to keep as much as possible of the palatable thick fleshy part. Then the fibrous points and edges of the leaves are removed and the leaves are chaffed in pieces not larger than 50 × 100 mm, using a chaff-cutter or chopping knives (De Kock, 1980).

Environmental impact

Soil protection

Agave americana is planted as a hedge plant along contours to stabilize platforms and to prevent or control erosion, and for reclamation of denuded and overgrazed land. It is planted as a barrier to prevent fire dispersion (Oudhia, 2007, de la Torre et al., 2018).

Invasive plant

Agave americana is considered a noxious invasive weed in many countries in southern Africa, including South Africa (Oudhia, 2007). As an invasive plant, its large leaves shade out native species and its dense network of rhizome offshoots draw resources away from them. Its rhizomatous nature may alter the nutrient status of the soil. In South Australia, it harbours introduced animal species, such as rabbits, making feral animal control more difficult. Control is carried out by combining physical removal and herbicide treatement (GISD, 2020).

Nutritional aspects

Nutritional attributes

Agave americana is a succulent plant. Its leaves have a high moisture content (88-90%), which makes them a source of water in dry conditions (McDaniel, 1985; King et al., 2011). Agave americana leaves have a low to medium protein content (3-9% DM), a relatively low NDF content (16-37% DM), and a high sugar content (50% DM) (King et al., 2011; Nasri et al., 2012; Santra et al., 2019; McDaniel, 1985).

Potential constraints

Toxicity

Several cases of poisoning have been reported in Australia after cattle had consumed Agave americana leaves due to the lack of green feed. This toxicity manifested itself as a myopathy and mainly affected the hindlimbs. Most cases recovered (Love et al., 1994).

Saponins

Agave americana leaves contain saponins (Nasri et al., 2012), which eliminate ciliate protozoa in vitro from rumen at a level of 2% on DM basis within 2 hours in the rumen liquor (Santra et al., 2019).

Oxalates

Agave americana leaves contain needle-like calcium oxalate crystals, called raphides, which can cause contact dermatitis and conjunctivitis (Oudhia, 2007). When ingested, oxalates link with calcium ions, making calcium unavailable for the animal. Three situations have been described (Hobson, 2016):

Unadapted animals eating excessive amounts of Agave americana may suffer from hypocalcaemia, resulting in weakness, paralysis and eventually death. The blockage and damage of kidney tubuli by Ca-oxalate crystals is a cause of kidney failure.
In adapted animals, excessive amounts of oxalates are absorbed and not all oxalates are detoxified in the rumen. Calcium deficiency will result in bone abnormality, poor milk production, poor growth, kidney and bladder stones, and gastrointestinal stasis.
Excessive intake of leaves can result in acidosis, probably due to the total sugar content and the rapid digestibility of the fibre, which in turn may cause lameness, as in the case of grain-based diets.

It is thus recommended to avoid sudden exposure to the plant and to limit intake, to avoid giving it as the only feed, and to supplement the diet with calcium sources (dicalcium phosphate as a lick or mixed in the supplementary feed, addition of lime).

Antifertility compounds

Antifertility compounds (anordin and dinordin) have been identified in Agave americana leaves (Crabbe, 1979; Hackman et al., 2006).

Ruminants

Leaves of Agave americana are used for livestock feeding raised under harsh conditions in several countries (De Kock, 1980). Notably, leaves, floral stalk, heart and roots are used as livestock fodder in several South American countries. Leaves are one of the main feed resources in central Andes and one plant can provide fodder up to four cows per week (de la Torre et al., 2018). Farmers in Peru use Agave americana as feed for cattle because of its vitamin content and good forage (Venero, 2006). Agave americana is used as a drought feed by South African sheep farmers in the Karoo region (Hobson, 2016). There are recorded instances of hungry cattle browsing fences of Agave americana in Australia (Love et al., 1994) and in India (Pathak, 1965).

Palatability

American agave leaves, once prepared, are palatable and can form a portion of the daily ration (De Kock, 1980).

Digestibility

The in vitro DM digestibility of Agave americana leaves is relatively high (61%), which makes them a potentially good forage for ruminants (Santra et al., 2019).

Utilization

Due to their low protein content and high water content, Agave americana leaves alone are not sufficient for a maintenance ration. They must be supplemented by sufficient alfalfa hay and other feeds to prevent the noxious effects of oxalates, which can be experienced if they are fed alone and continuously. Agave americana leaves can, to a large extent, take the place of silage, fodder beets etc, as the succulent portion of the ration (De Kock, 1980). A study in South Africa showed that Agave americana leaves could satisfy 64% of the maintenance requirements of mature sheep, but that the best results were obtained at an inclusion level of 45% in maintenance diets with 55% alfalfa (Hobson, 2016).

One major disavantage of Agave americana leaves is their high water content, which results in a low DM intake. In a trial in South Africa with adult Dorper ewes fed with fresh, wilted or dried leaves, wilting or drying failed to improve DM intake, which actually decreased from 615 g/d (fresh forage) to 561 g/d (dried forage). Water intake was almost null with fresh leaves (0.11 L/d) compared to dried leaves (1.27 L/d). In any case, fresh or dried leaves fed alone could not maintain body weight (-160 to -192 g/d) (King et al., 2011).

When female lambs are supplemented with 120 to 360 mg of saponins extracts from Agave americana leaves, DM intake, diet digestibility and daily weight gain were not modified (Nasri et al., 2012).

Pigs

Information about the use of Agave americana for pigs is almost inexistant. An article from former Yougoslavia mentions feeding pigs with the fleshy part of the leaves, peeled and chopped (to remove the oxalates), and cooked with the addition of salt and bran (Kovacevic et al., 1963).

Poultry

Ostriches

In South Africa, Agave americana was investigated as a dietary supplement in diets for ostriches. Agave leaves cut daily from the main plant and chopped into small blocks had a TME value of 12.2 MJ/kg DM, about 80% of the value of maize. It was suggested that in more extensive feeding conditions Agave americana could be used as a feed supplement for maize in birds aged 6 months (Cilliers, 1998).

Rabbits

No information seems available in the international literature on the use of Agave americana in rabbit feeding (as of June 2020). This succulent plant is eaten by wild rabbits during drought periods in Arizona, sometimes so severely that plant dies (Kelly et al., 2011). As shown in the Ruminants section, Agave americana is used to feed livestock in different countries. For these reasons, Agave americana must be considered as a potential low-protein forage for adult or growing rabbits. The antifugal and antibacterial compounds found in Agave americana extracts could be of interest to control rabbit health (Santos-Zea et al., 2012; Condor Quispe, 2018). However, as mentioned in Potential constraints, Agave americana leaves contain antifertility substances. For that reason, feeding trials are absolutely necessary to assess their safety before using them to feed breeding rabbits does.

Nutritional tables

Tables of chemical composition and nutritional value

Century plant (Agave americana), leaves, fresh

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used