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April 2011 cover image Paddle On!

Flora Fact: Desert Date

Yucca and yucca moth rely on each other for reproduction.

By Sheryl Smith-Rodgers

Attention, wildflower watchers. This spring, take heed of Texas paintbrushes, particularly those intermingled with bluebonnets. Because — gasp! — we’re about to expose a dark side to their scarlet beauty.

Across West Texas and into the rolling Hill Country, approximately 15 species of native yuccas occur, ranging from prickly mounds to multibranched trees. In spring and early summer, they produce a tall, slender stalk that unfolds into a spectacular cluster of creamy white blossoms.

Mention yucca to a rancher, though, and he may say a bad word or two. That’s because some yuccas can form dense stands and invade grasslands.

Not Torrey’s yucca (Yucca torreyi). Native to the desert scrublands of the Trans-Pecos region, this branched species can reach more than 20 feet tall. Like all yuccas, Torrey’s yucca (named for 19th century botanist John Torrey) belongs to the agave family. Its spiny, concave leaves grow up to 4 feet long. Lower ones die off, droop and form a grassy skirt around the yucca.

Yuccas fascinate both biologists and entomologists.

“[Yuccas] have a remarkable relationship with yucca moth species of the genera Tegeticula,” says Rick Hammer, a biology professor at Hardin-Simmons University in Abilene. “Both totally rely on each other for reproduction.”

At dusk, a female yucca moth collects pollen from yucca flowers, using unique mouthparts called tentacles. She then flies her pollen lump to another yucca, where she selects a bloom and deposits her eggs inside the ovary. When done, she pollinates the flower with her pollen. Both benefit. Her larvae feed on the seeds but not all of them. Enough survive to ensure more yucca progeny.

 


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