Aloe and Agave are two genera of succulent plants with similar appearances and care needs. The similarities arise because both adapted to live in hot, dry climates. Aloe and Agave, however, are not closely related, and the similar climates in which they evolved are in different hemispheres of the world.
Aloe is a genus in the family Asphodelaceae. The members of this genus have juicy leaves arranged in a rosette. Agave also has juicy leaves arranged in a rosette. Agave, however, is a member of the family Asparagaceae.
Aloes are an "Old World" plants. They originally grew in sub-Saharan Africa, on the Saudi Arabian Peninsula, and in Madagascar. From there, Aloes spread along the Mediterranean coast and South Africa. Though Aloes grow wild in the southwestern United States, they grow as an introduced species, not as a native one. Agaves, on the other hand, are "New World" plants. They originated in Mexico and the American Southwest. Today they extend from Utah into northern South America, growing in deserts, arid grasslands, and oak-pine woodlands.
Aloes grow well in USDA Plant Hardiness Zones 9 through 11. Agaves grow in zones 9 and 10, with some varieties tolerating more heat or cold than the norm. Agaves can tolerate full sun. Aloes like a bit of shade during the sunniest times of the day. Both plants do well in sandy or even rocky soil if it is well-drained.
It is easy to confuse Aloe and Agave at first glance, but some typical physical differences can point you in the right direction. For the most part, Agaves are larger and spinier than Aloe. The spines on Agaves are often painfully sharp, whereas the "teeth" that sometimes line Aloe leaves are usually soft to the touch.
For a sure-fired diagnostic, try snapping a leaf in two. An Aloe will break easily, giving you access to the gel stored inside. On the other hand, Agave leaves are highly fibrous, and sharp shears are required to cut them.
The flowers of Aloes are tubular, making them perfect for pollination by long-beaked birds. They grow in clusters atop long stalks. The flowers typically bloom in spring or summer and range in color from creamy white to orange, bright red, or purple.
Agaves also flower atop a long stalk that shoots up from the center of the rosette. This flowering structure, called an inflorescence, is often as big or bigger than the plant that produces it. It carries a bushy grouping of flowers at the top. The resources the inflorescence takes are massive. Expending them typically kills the plant. In other words, Agaves flower themselves to death. Consequently, they bloom only once in their lives, usually after 10 to 30 years, though sometimes after a much longer life, earning the common name "Century Plant."
Sources: sfgate.com, Mountain Crest Gardens
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