Within the California Floristic Province, there about 90 species of native tarweeds. Over millions of years, they developed to succeed in a variety of microclimates from sea level to mountain elevations. Tarweeds are part of California’s first native plants and are members of the sunflower family.
“Large swaths of undeveloped California are populated with all variety of tarweeds, because tarweeds have that logic in their DNA.” – Eric Simmons, Bay Nature Magazine
Tarweed, Hemizonia fitchii, is also known as tarplant, spikeweed, or Fitch’s Spikeweed.
They are part healthy grassland ecosystems. They’re also commonly found in areas where the soil has been disturbed.
Spikeweeds are annuals and drought-tolerant in the extreme. Seeds don’t require water to germinate!
Stalks and leaves are covered with fine hair and oil glands. A strong aroma is produced by the oil. Some folks claim it smells like turpentine, this blogger thinks it smells like eucalyptus. Tarplant oil may contain mosquito repellant properties.
Like other plants that make sticky oils, tarweeds attract certain bugs. Once they become stuck, they become carrion for predator insects that have evolved along with the tarplant, able to move about unhampered. Some of the carrion is eaten by predators while others may become nutrient sources for the plant.
Seeds are edible, like sunflower seeds. They can be eaten raw, toasted, or ground into flour. Native Americans used them to make mush. Birds and other animals also enjoy this food source.
At knee height, tarplants are eaten by grazing animals when they’re freshly sprouted, but later in the season when spikes are fully developed at the end of stem leaves, most grazers avoid them.
The California Floristic Provinceis considered a world biodiversity hotspot. It contains a large number of ecosystems that include alpine forest, mixed evergreen forest, riparian forest, sagebrush steppe, coastal sage scrub, redwood forests and more.
Currently, only 25% of the original vegetation remains unharmed.
Fragmentation [human building] has the capacity to generate persistent, deleterious, and often unpredicted outcomes, including surprising surges in abundance of some species and the pattern that long temporal scales are required to discern many strong system responses. National Center for Biotechnology Information
Characteristics of Invasive Species
successful invasion elsewhere
ability to live near humans
food source variety
survives in a wide range of environments
alters growth to suit changing conditions
grows and reproduces quickly
fast spreading
difficult to eradicate
Invasive species and biodiversity preservation is a topic much larger than one blog post can cover! Below is a brief list of plants commonly found in Nevada County.
The ‘Resources’ section at the bottom of the page contains links for extensive exploration.
Creates an impenetrable thicket (bramble).
Grows in areas where soil has been disturbed such as land grading, agriculture tillage, timber logging, housing construction, wildland firebreaks, animal grazing, and road building.
Provides shelter for rats and food for deer.
Damages livestock.
Sri Lanka / Korea. Imported as an aquarium plant in the 1950s
Behavior
Aggressively invades new aquatic environments.
Displaces native vegetation.
Forms large dense mats.
Impedes water flow.
Cloggs pumps.
Reduces water clarity.
Alters the ecosystem.
Blocks sunlight.
Decreases oxygen water levels, killing fish.
Reduces recreational water use.
Fragments easily carried to new waterways.
Impedes waterfowl feeding.
Impedes fish spawning.
Devalues waterfront property values.
Impedes water treatment and power generation.
Chilean-harvested alfalfa imported during the California Gold Rush.
Behavior
Grows in areas where soil has been disturbed such as land grading, agriculture tillage, timber logging, housing construction, wildland firebreaks, animal grazing, and road building.
One plant can produce nearly 75,000 seeds.
Alters water cycles.
Poisons livestock.
Overtakes native plants.
Imported from Europe in the mid-1800s as a land stabilizer and garden accent.
Behavior
Aggressively displaces native plant populations.
Highly flammable.
Fire hazard.
Seeds can remain active for over 80 years.
A mature shrub can produce up to 15,000 seeds.
Seeds can be transported over long distances by animals, water, vehicles, and people.
Grows in a variety of soil conditions.
As a legume, it changes soil chemistry.
After removal, native plants won’t repopulate.
Not pervasive, yet, in California, these animals have caused large-scale agriculture, water and forest management, and recreational problems in other states.
Carefully inspecting possessions after traveling from infested areas, and cooperation with Agriculture Inspection Station agents are ways to help prevent a species invasion.
Caspian and the Black Sea and Dnieper River, Ukraine. Brought into the Great Lakes in the 1990s through ship ballast water.
Behavior
Disrupts ecological water balance.
Reduces recreational value, shells overrun sandy beaches.
Impedes water flow.
Encrusts pipes and other structures.
One muscle can produce 5,000,000 eggs during its 5-year lifespan.
Estimated Five billion community costs since first discovery.
Europe and Asia. Escaped from breeding experiments in Massachusetts in the 1960s.
Behavior
Voraciously eats tree leaves and shrubs.
A single moth can consume a square foot of leaves per day.
Leaves caterpillars eat – cedar, pine, fir, spruce, aspen, oaks, birch, alder, manzanita, and western hemlock.
There is an urgent need for conservation and restoration measures to improve landscape connectivity, which will reduce extinction rates and help maintain ecosystem services. National Center for Biotechnology Information
Tarweed, Hemizonia fitchii, is also known as tarplant, spikeweed, or Fitch’s Spikeweed.
