The Grand Defiance of Agave Blooms | KCET
The Grand Defiance of Agave Blooms
It was the developing stalk of a flower, growing out of one of my neighbors' Agaves.
The agave in question isn't native to this part of the desert. It's an Agave americana, originally hailing from the highlands of Central Mexico but planted worldwide over the last 250 years or so. You see them dominating coastal California gardens, breaking stucco retaining walls, and perforating the shins of the unwary along neglected sidewalks.
In places with a little bit more water than we have here in Joshua Tree, where an Agave americana can grow to be eight feet across or so, the species' flower stalk can reach heights of 30 feet. The one in my neighborhood will be lucky to reach 20 feet; it takes a lot of metabolic resources to grow a stalk that high, and local agaves struggle to put on growth even in non-blooming years. Blooming can use up resources equivalent to a full year normal growth, or more. Water and sugar and minerals that had been stored in the plants' fleshy leaves and roots go into erecting the plants' floral pillars. the agave depletes itself to build that flower stalk. After blooming there's nothing left; the plant dies.
Biologists refer to this "all or nothing" strategy of reproduction as semelparity. It's a sensible way of maximizing the amount of resources that go into creating the next generation of your species, as long as you don't plan to get to know your kids. It's a poetic gesture: putting everything you have into reproduction and then dying, the botanical equivalent of a salmon swimming upstream to spawn and then succumbing to the ordeal.
Agave americana was imported into the California deserts, but two of its cousins got here on their own: Agave deserti, whose rosettes of spiny leaves get to about two feet tall and wide at most, and Agave utahensis, whose several California varieties are the size of soccer balls or smaller. Both are found at upper elevations in the easternmost parts of the California section of the Mojave Desert, and Agave deserti also grows from the Santa Rosa Mountains south through Anza-Borrego and into Baja.
Outside the desert there's one more California Native species of agave: Agave shawii, which just barely hangs on along the San Diego coast. It's more prevalent in Baja: urban development of chaparral coastal bluffs has depleted the plant's U.S. habitat. And that's it for the Golden State, which is relatively devoid of agaves compared to places like Arizona, which has 40 or so native species. Texas and Mexico have even more. There are about 135 species of agave native to North America, and only three are native to California, one only by the skin of its teeth. It hardly seems fair.
Despite the possibility of longevity through cloning, most agaves don't come anywhere close to deserving their common name of "century plant," based on folklore that the plants grow for 100 years before making that grand, defiant reproductive gesture. Agave deserti's lifespan tends to run no longer than 50 years. Agave americana's is more like 30. I don't seem to be able to find a reference that ventures an opinion on the lifespan-before-flowering of Agave utahensis, but based on the number of ten-foot flower stalks I see in most clumps of the species I'd venture a guess of less than 40 years.
Evolutionary pressure to attract those pollinating animals, in other words, likely encouraged the ancestors of our present-day agaves to grow taller and taller flower stalks to compete with their kin. At some point this internecine arms race reached a critical threshold, as arms races generally do: the ancestral agaves started building flower stalks so tall that they didn't survive the process.
As long as a few seedlings survived, though, it didn't matter. All that matters to evolution is the continuation of the species. Very few agave seeds grow to maturity; only those lucky few that land in a sheltering nurse plant in a year with the right combination of moisture and temperature will sprout, and only a very small percentage of those will make it through their first year.
With clumps of agaves sending up flower stalks each of which might scatter several thousand seeds across the landscape, the math just barely works out in favor of survival.
Last year she told me that the plant had just died without blooming, and she'd had to hire a crew to come out and remove it. She didn't mention whether there were any offsets left.
For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.
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