The distinctive silhouette of teasel (Dipsacus sativus) is a familiar sight in the coastal parts of California. Thick, pointed bracts jut out, like splayed arms beneath the cone-shaped flower head. This structure stays standing long after the small white flowers have faded; people collect the dried stems for decoration. The spiny flower heads are so stiff they were used to card wool before metal carding combs were created!
Sadly this odd-looking plant is also a fairly nasty invasive. It can form dense chest-high thickets that are impassable to both people and animals. This European invasive likes to grow in disturbed areas: along roadways, in ditches and on grasslands. Another species, wild teasel (Dipsacus fullonum) is less common locally but more widespread throughout North America. It has pink-to-purple flowers and sharply upcurved bracts. Just to confuse things, both species also go by the common name of Fuller’s teasel.
One of the most common thistles around is bull thistle, an invasive species from Europe. Its showy purple flowers are beloved by bumble bees and other insects, but its spiny leaves are a bane to ranchers.
Bull thistle (Cirsium vulgare) grows most abundantly in coastal grasslands, along the edge of marshes, and in sunny openings in forests, according to the California Invasive Plant Council – but it is found in every state in the country. You can recognize this species because the leaves don’t stop when they meet the stem; instead they run down along it like little spiny wings.
This plant thrives on disturbance; it grows most readily when the soil is disrupted by plowing, logging, digging and so on. Even gopher activity can give it a boost!
A wash of prickly, pale green stems is scattered across a dry field. Yellow flowers are surrounded by a mean halo of long narrow thorns. Here is yellow star-thistle (Centaurea solistalis) one of the nastiest invasive plants around. It’s a big problem on farmland and in wild places along the west coast. It interferes with grazing, and eventually leads to permanent brain damage in horses that eat it.
Introduced in the 1850s, this thistle is now the most widespread invasive plant in California, infesting between 10 and 15 million acres in the state. A native to southern Europe, it probably first came to the US indirectly, along with alfalfa seed imported from Chile. By the early 1900s it was a serious weed in the Sacramento Valley and was spreading quickly along roads, railways, trails and streams, according to the CalIPC. “It is a thousand times as common as ten years ago, and perhaps even six years ago,” observed Willis Jepson in 1919.
Things have only gone downhill from there! And it’s not surprising why. This deeply taprooted annual invades summer-dry grasslands across most of the US. A single large plant can produce nearly 75,000 seeds, and blooms from late spring through fall. It’s largely pollinated by honeybees but doesn’t have much in the way of predators, and so it continues to spread.
With flamboyant, showy flowers, Spanish broom is probably the most beautiful of all the evil brooms. It is still evil, though. Don’t be fooled by the big yellow flowers with their many exuberant stamens and pretty wing-like petals.
This plant has the lean, linear look of Scotch broom but with even fewer leaves. The California Invasive Plant Council lists Spanish broom (Spartium junceum) as a species that can cause serious problems for native ecosystems. It can grow up to 15 feet tall and form dense stands that smother all other plants in the area. According the IPC, it is native to Spain, Morocco and other parts of southern Europe. It was introduced to California in 1848 as a decorative plant, and in the 1930s was planted along mountain highways in Southern California. Oops.
In Marin, it is one of the least common brooms. I saw the ones pictured here clinging to the slopes of what looks like an old rock quarry owned by the Marin Municipal Water District.
You’ll see these towering purple spikes looming from road cuts and clifftops. This is pride of Madeira, or Echium candicans. It’s a common sight – especially in more coastal areas. It grows to more than seven feet tall, and is very striking with its gray-green leaves and massive heads of flowers (easily over a foot long).
Sadly, this plant isn’t native to the US. It’s another escaped ornamental species that’s still commonly used in landscaping. Birds and butterflies love it, and deer don’t. In inland areas this isn’t a problem but in the coastal climate it spreads on its own, gradually creeping into wild areas. Because it spreads slowly it is only considered to be moderately invasive, but it’s still not recommended for local gardens.
Hiking across a remote meadow, I suddenly find myself in a knee-high field of daisies. This is the invasive oxeye daisy (Leucanthemum vulgare), a striking flower with stark white petals around a yellow center.
This bloom was introduced from Europe and is now widespread throughout Marin and much of California. It has a cousin, Shasta daisy, which is less common and has (very slightly) larger flowers and leaves. Oxeye daisy is a moderately problematic invasive, growing so densely in places that it excludes other native vegetation. It also is known for giving cows’ milk an unpleasant taste if they eat it.
The brown hills of California are far from monochromatic. Look closely and you’ll see a complex tapestry of colors, textures, shapes, sizes–and sounds! Do you hear that rustling rattle as you brush through the grass? Look close and you’ll see graceful stalks of rattle-shaped grass heads.
This is rattlesnake grass, or Briza maxima—one of my favorite plants of the summer. Sadly this nice-looking plant is also fairly invasive (introduced from Europe, and occasionally planted as an ornamental). It’s now become naturalized in the Coast Range and in scattered other parts of California, which is why you see it almost everywhere.
Showy pink blossoms, delicate fragrance and winding tendrils – it’s sweet pea season. I’ve been seeing them growing along roads and trails, in gardens, and in bouquets on people’s tables or shop counters. This is an invasive species that it’s hard not to love – a guilty botanical pleasure!
As with yesterday’s plant, this is one where I learned more than I bargained for in the identification. I had naively assumed that there was only one type of sweet pea and that every time I saw that distinctive pink blossom it was the same species. Wrong again! There are several different kinds, and also some native species with paler pink blooms, so you have to look close. Tangier pea, or Lathyrus tingitanus, has the winged stem, two-parted leaves and large, deep pink flowers that mark it as one of the non-native species. You can tell Tangier pea from sweet pea because it is an annual, and also because it only has two or three blossoms per stalk.
This is another badnasty invasive broom species that you’ll see frequently throughout the Bay Area. Scotch broom (Cytisus scoparius) has pretty yellow pea-like flowers and long, narrow leaves that press closely against its multi-sided stems. Though it occasionally has some rounded leaflets as well, the overall lean, linear look to its foliage makes it easy to tell from its French broom cousin that I wrote about a few weeks ago.
In California, French broom is a nastier problem than Scotch broom, but throughout the rest of the country the Scottish Cytisus scoparius is the worst broom around. Even worse, both were deliberately originally introduced as ornamental species!
This plant is so nasty because it is hearty and vigorous, and spreads fast because it produces a LOT of seeds. A single Scotch broom plant can live for up to 7 years, and produce over 150,000 seeds per year. It’s a mind-boggling number! The seeds stay in the ground, ready to sprout, for between 5 and 30 years. These plants grow up to 12 feet tall and smother any native plants that would otherwise have grown where they are. There’s no sharing if you’re a broom species! Scotch broom is a rampant invasive across much of the western and eastern seaboards of North America – from Alaska to Baja and from Maine to Georgia, as well as in other countries like Australia and New Zealand. It’s native to northern Africa and parts of Europe.
There is one more broom species that you might see in the area, and that’s Portuguese broom. It’s not nearly as common, but it does cover about 65 acres in the Marin Headlands where it was planted in the 1960s as part of a landscaping and slope stabilization program – another good idea gone wrong! Portuguese broom looks a lot like Scotch broom, except the seed pods are inflated instead of compressed around the seeds. Also they have 8-10 sided twigs, as opposed to the 5-sided twigs of Scotch broom.
Long beaked stork’s bill is a ubiquitous sight in the fields of the bay area. This invasive little weed and its cousins, other types of stork’s bills, have naturalized across most of California. The long beaked stork’s bill (Erodium botrys) is distinctive because of the particularly long, beak-like seed pod, but also because of its leaf – it is the only one with a long narrow leaf that isn’t actually dissected into separate leaflets.
There are several species of wild geraniums with flowers that look quite a bit like those of stork’s bills – small, pinkish-purple. Again, look to the leaf to know what plant it is. The geraniums (sometimes called crane’s bills) have deeply dissected leaves that are overall roundish in shape. In other words, if you drew a line around the outside of the leaf, ignoring the details, you’d come up with a circle as opposed to the overall tongue-shaped leaves of the stork’s bills. The wild geranium petals are usually notched at the end, giving them a toothed look. Almost all of the wild geraniums are also invasive, with a few exceptions.