Pesky plants

Stinging nettle

URTICA DIOICA

At first glance, the leaves of stinging nettle appear as inviting as mint, but casual contact transmits a burning sensation that can linger for days. The hairs are packed with a potent brew of histamine, acetylcholine and serotonin that causes an allergic reaction in mammals. To ease the “bite,” rub leaves of coyotebrush, which grows on dry hillsides near the nettle, on affected skin. But stinging nettle has other properties that challenge our desire to label it a nuisance. The plant’s juices are reportedly beneficial: as an excellent hair tonic, to reinvigorate the liver and kidneys, to stimulate milk in nursing mothers and to treat prostatic hyperplasia.

Key characteristics: A stout, handsome plant 3 to 10 feet tall. Has opposite leaves with serrated edges, square stems (in cross section) and delicate sprays of loosely hanging flowers.

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Catsclaw

ACACIA GREGGII

When a plant lives in the desert but has tender, tasty leaves preferred by every grazing animal in the area, it has to protect itself. Hence the elegant, albeit annoying, solution devised by the aptly named catsclaw. Armed with an array of spines curled like the claws of a cat, this plant readily hooks and tears the sturdiest clothes. Growing 10 to 30 feet tall, catsclaw grows along desert washes where its waxy seeds tumble and scar in abrasive flash floods before they germinate. Overgrazing or absence of wildfire leads to dense thickets. Catsclaw, which blooms in April, provides shade and cover for birds and wildlife.

Key characteristics: Bare-limbed all winter but covered with tiny, gray-green pinnate leaves from spring through fall; dense spikes of flowers form flat, pea-like pods that constrict to reveal the outline of each seed. Thorns are scattered along branches and interspersed with leaves.

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Teddy

bear

cholla

OPUNTIA BIGELOVII

Looking deceptively soft at a distance, the teddy bear cholla of Southern California deserts lures unsuspecting hikers, then snags them with horrific spines, which is how cholla reproduces itself. These chunks, when shaken loose, send out roots and grow into clones of the original plant.

Cholla spines are so dense that little of the plant’s surface can be seen. They function as shields against the sun’s intense rays, and are so effective that the cholla can tolerate some of the highest temperatures of any vascular plant.

Key characteristics: A 3- to 5-foot-tall, many-branched cactus that turns black or brown on its lower stem, while its upper branches shimmer golden or silvery from the reflection of its many spines.

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Poison

oak

TOXICODENDRON DIVERSILOBUM

Hikers may not know urushiol, but this oily substance is the bane of their outdoor life. As the active ingredient in one of California’s most abundant trailside plants, it is the poison in poison oak, the most hazardous plant in California in terms of hours lost and workers’ compensation claims filed. About 70% of the population is susceptible to the acute itching caused by poison oak, and almost 15% have allergic reactions to the plant.

Poison oak thrives in a disturbed environment, which probably accounts for it being one of the most widespread and abundant plants in the state.

Key characteristics: Although poison oak is best known for having three leaflets that look like oak leaves, it ranges from being a low shrub to a sprawling vine that disappears into a canopy of trees.

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Poodledog

bush

TURRICULA PARRYI

After a wildfire, the dry ridges of Southern California may be invaded by the quaintly named poodledog bush. But all charm ends here, for the sticky and ill-scented poodledog is covered with stiff microscopic hairs that deliver a noxious punch. These glandular hairs, known as trichomes, discourage herbivores and plague passing hikers who brush up against the foliage. The chemicals — prenylated phenolics — emitted by the hairs cause dermatitis and an inflammation similar to that caused by poison oak. The scientific name Turricula means “little tower” in reference to the stalk of deep blue flowers that rises over the plant in the spring.

Key characteristics: This stout and densely leafed plant can form thickets growing nearly 10 feet tall. The long linear leaves may be rolled under along their margins.