Agave

The big, armed agave of Mexico and the far southern United States, also called American aloe or maguey: a huge rosette of thick, grey-green to blue-green leaves, each edged with hooked teeth and ending in a sharp spine. Despite the name it does not take a century to flower; outdoor plants bloom once, usually between their tenth and twenty-fifth years, on a stalk 15 to 30 feet tall, and then die, leaving offsets behind. It is hardy outdoors only in USDA zones 8 to 11; everywhere colder it is a container plant that winters indoors and stays much smaller. It has escaped from gardens and naturalised in warm regions around the world.

A soft, spineless agave from the mountains of central and western Mexico, also called lion's tail or swan's neck agave: a broad rosette of pale grey-green leaves with no marginal teeth and no terminal spine, which slowly rises on a short trunk and gathers offsets into a clump. After about ten years a rosette sends up one long, arching flower spike, then dies and leaves its offsets behind. It is frost tender: the Missouri Botanical Garden rates it for USDA zones 10 to 12 only, so outside the warmest gardens it is a container plant that spends the winter indoors.

A rosette-forming evergreen succulent native to the grasslands, desert scrub, and pinyon-juniper woodlands of Arizona, New Mexico, Texas, and northern Mexico at 4,000 to 8,000 feet. Thick, rigid blue-gray leaves with toothed margins and a one-inch terminal spine form a dense, symmetrical basal rosette to about 24 inches tall by 3 feet wide. Surprisingly cold-hardy for a succulent - reliably hardy to USDA Zone 7 and reported to survive -20°F as long as the cold is dry rather than wet. Each rosette flowers only once, after 10-30 years, sending up a single 20-foot stalk before dying and leaving its rooted offsets behind.