Agave species: Century plant

Family

Agavaceae

Common Name

Agave, century plant, American aloe, sisal, maguey.

Plant Description

Primarily plants of the desert areas of the southwestern United States, Mexico, and the Caribbean islands, many of the Agave (300 species) have become popular in xeriscape landscaping, and occasionally as houseplants. These long-lived perennial plants vary considerably in size, the leaves ranging from 1 - 2 in. to 4 - 5 ft. in length. The leaves are fleshy, smooth, alternate, generally sword-shaped, often with sharply toothed leaf edges and a terminal spine (Fig. 27 and Fig. 28). Small species may take up to 5 years to produce a flower spike while some of the large species may not flower for up to 50 years. Each plant only flowers once in its lifetime, and after flowering dies, but produces offsets that maintain the plant. The numerous flowers are produced on tall spikes or racemes. Fruits are capsules or berries containing numerous seeds.

Figure 27. Agave lecheguilla.

Figure 28. Agave parryi.

Toxic Principle and Mechanism of Action

The only species of Agave known to cause poisoning in animals is A. lecheguilla (lecheguilla) and its toxicity is due to the presence of hepatotoxic sapogenins [1]. These compounds affect the liver's ability to excrete the photodynamic compound phylloerythrin via the biliary system. Cholestasis appears to result from the accumulation of calcium sapogenin salts in the bilary ducts [2]. Sheep, goats, and cattle become affected after they have consumed the plant over several weeks. Many species of agave contain steroidal sapogenins and therefore have the potential for causing poisoning in animals.

Risk Assessment

It is unlikely that household pets would consume enough of the agave leaves to cause liver toxicity. However, the sapogenins may stimulate excessive salvation, and the many sharp spines on the leaf margins and tips of the leaves may cause trauma to the mouths of animals that chew on them.

Clinical Signs

Sheep, goats, and cattle are affected after they have consumed the plant over several weeks. In these species, cholestasis and biliary obstruction can cause icterus and signs of secondary photosensitization. Recovery of affected animals depends upon the chronicity of the poisoning, and since there is no specific treatment, affected animals should be kept out of the sun and fed a more nutritious diet.