Invasive Plants of California's Wildland

Helichrysum is a white-woolly, sprawling, waist-high shrub that is capable of climbing. It has aromatic leaves the size of a nickel or a quarter, densely matted on both surfaces with soft white hairs, making the plant appear white. This whiteness makes it easy to spot infestations from a distance. Its cream-colored flowers are in densely clustered heads that resemble those of native everlastings and especially cudweeds (Gnaphalium spp.), although native cudweeds are much smaller than this plant.

Helichrysum has been reported outside cultivation in four locations in California, all within a few miles of the ocean in Monterey, Marin, and Mendocino counties. The Monterey infestation is in the Del Monte Forest, the two Marin populations are within the Golden Gate National Recreation Area, and the Mendocino population is near Gualala (Howell 1969; Smith and Wheeler 1990). The plant invades coastal scrub communities, but has the potential to invade coastal grasslands. It is sun-loving, and it is unlikely to tolerate much shade.

The species’ known tolerances (mild winters and summers) indicate that it has the potential to invade along the California coast to a few miles inland, especially the south and central coast. It thrives in either sandy or heavy soil. Because it is a garden plant, special efforts should be made to locate incipient infestations near human habitations in the coastal belt.

Helichrysum petiolare is indigenous to the coastal belt at the extreme southern tip of Africa. It was offered by specialist nurseries in the 1960s, and present infestations are undoubtedly garden escapes. Vegetative propagation may be an important means of spreading because branches can root if in contact with the ground. Seeds are wind-dispersed, but they generally do not carry long distances.

The Stinson Beach infestation in Golden Gate National Recreation Area demonstrates that Helichrysum petiolare can invade undisturbed sites, since it is penetrating an otherwise apparently healthy, dense California sagebrush-coyote brush scrub. It forms a closed canopy in places and displaces native plant species.

Helichrysum petiolare spreads vegetatively and by seed. Flowering is in mid-summer, and abundant seed is produced by early autumn; seed longevity is not known. Its branches are lax and sprawling, and those touching ground will take root, hence vegetative propagation may be an important means of spread in California.

Seed germination, as with most Mediterranean-climate plants, is in fall after the first rains. Plants grow actively in spring and early summer; they flower in mid-summer followed by seed set, after which they are semi-dormant (Sunset 1988).

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There have been no reported efforts to control Helichrysum petiolare. Small infestations are easily removed by hand pulling. For large patches, it will be necessary to experiment with an herbicidal application. The dense woolly hairs protecting the leaves may inhibit absorption of many herbicides. A certified herbicide applicator should be able to assist in selection of an effective surfactant. It is not known whether this species is adapted to regenerate from seed or root crowns following fire.