California Native Plant Society
in collaboration with East Bay Municipal Utility District
July 26, 2019
With a long, cool spring and those late May rains, we've had glorious wildflowers all through this month; Sticky Monkey and Farewell-to-spring have just been stunning. We've been busy chasing down many invasives, and lately focusing on Scattergrass (Ehrharta) under the Bays along the ridge. On July 12th, we had a big corporate workday with the Ridge Trail and MSCI group, where 23 of us hauled all the logging debris off the Northern Triangle (above Siesta Gate). Once all that brush is chipped up, we'll be ready to start restoration with the rains.
We're still going out twice a week: Sunday mornings at 9:30 am and Wednesday afternoons at 4 pm. Please let me know if you can make it.
Our native red thistles, the big, tall silver ones with the candy-apple red flowers have been really great this past month. Botanically, these are Cirsium occidentale; common names are Cobweb Thistle or Western Thistle. Blooming late in the season, usually in June, these are a keystone species in terms of all the many forms of life they support. Here's a group of them:
These flowers are borne on stalks up to three feet tall, and one plant can have up to fifteen flowers. (Photo thanks to Bill.) They grow in the hottest, rockiest and windiest of places at Skyline, especially along the ridge of Barberry Peak. It's hard to imagine how how such large plants can grow in the toughest and driest of places, but whenever I mention the Barberry Peak area, people respond, almost without fail, "Oh, that's where the big, red thistles grow." They have such a searing beauty.
Here's a flower up close:
Just look at that red!! For me, these are the stars in the crown of the High Ridge area. (Photo thanks to Angela)
Cobweb thistles are basically biennials (grow leaves the first year, flower, seed and die the second year) so the flowers we see this year are actually from second year plants, blooming for the first time. This native species grows on rocky ridges up and down the state, and comes in several varieties and color forms:
The one at the left, deep red, is known as var. venustus, or Venus Thistle, and is probably the one we have at Skyline. The center and right, white and lavender, are known as var. californicum, sometimes seen near the coast, like at Pt. Reyes and further south. (This photo montage thanks to Mark Kummel) The heights of Mt. Diablo have many Cobweb thistles in the rocky scree areas and the color up there is pink to lavender.
While Cobweb thistles are striking and memorable to us people, to other creatures they sources full of pollen and nectar, and the brilliant flowers attract many species of wildlife. We've collected a number of photos to show this. Look here:
This is a female Anna's Hummingbird nectaring. We've actually seen them doing this up at Barberry Peak this year. (Photo thanks to Ken Hickman).
Any creatures with a long tongues are especially drawn to thistle nectar; especially butterflies:
Here's a double -- two Pale Swallowtails nectaring. (Thanks again to Mark Kummel for this photo!) Pale Swallowtails are so called because of the pale, moonlight color of their wings between the black stripes. These lay their eggs on plants in the Buckthorn family (Rhamnaceae), which includes Coffeeberry and Ceanothus. We see a lot of them up at Barberry. Some sixteen species of butterflies are known to nectar on Cobweb thistles.
Besides nourishing the large and showy creatures, native thistles are also food for many smaller ones; case in point:
Here's one of our plentiful, native Yellow-faced Bumblebees - head down and butt to the sky, deep in thistle country. Bumblebees have long tongues for nectaring in such hard to reach flowers as Lupines, Clovers, and thistles. Thistles are in the Aster family, and the flower heads are actually composites up to hundreds of individual flowers, each with their own drop of nectar deep down. This bumblebee stayed on this one thistle for over a minute, carefully moving just a bit each time to probe the next flower in the head. (Photo thanks to Margaret.)
Wildlife is drawn to Cobweb thistles for more than the nectar and pollen. Some species of butterflies lay their eggs on thistle leaves, and these become caterpillars:
We have found several kinds of caterpillars on thistles at Skyline. This dark one we believe to be either a Painted Lady or a Mylitta Crescent. These eat the leaves between the mid-rib and the spines, and then roll the leaf over to protect the chrysalis. (Photo Mark Kummel).
Some creatures live on the sap of the thistle plant:
This stem is just covered with aphids. And, if you look closely, you will see a number of black ants crawling around and over the aphids (there's even one at the tip of a spine, on the right). These aphids are special aphids, native to North America and Europe, known as Plum-Thistle aphids (Brachycaudus cardui ). In early spring, they live on trees and shrubs of the genus Prunus. Later on in the year, the adults fly to thistle stems. The ants are there to tend the aphids. They move them around, cultivate them, with the same purposes as people tend cows. The ants live on the honeydew that the aphids secrete. This seems to be mutually beneficial, as researchers have tried cultivating the aphids without the ants, and they just don't seem to make it. Any ideas on the species of this ant?
Wherever wildlife congregates, there are also bound to be predators:
This is a yellow Crab spider who has just grabbed a visiting fly. Of course, spiders would think of that. So do some birds, the flycatcher types, who also sit in wait. (Photo Mark Kummel)
So while all this web of life has been gathering and feasting on thistles and each other, what has Thistle been doing? Thistles have their own agenda, and here it is:
Seeds, yes, seeds; shiny, black thistle seeds, the next generation. Midst all the drama of the other wildlife, thistles have kept their eyes on the prize. These shiny, black seeds are like miniature sunflower seeds, and the resemblance makes sense; they are both in the Aster family. (Photo thanks to Cynthia.) Some of these seeds will be eaten by the Goldfinches who come and perch on the browning flower heads. Others will drift and scatter, and some will sprout with the rains, become rosettes next spring, and flower the year after.
Our Skyline Gardens effort has just passed it's three-year birthday, and during these three years we have paid special attention to expanding the numbers of rare and unusual species in the area, and especially to these native thistles along the ridge. In Year 1, we found a total of five blooming thistle plants in two distinct sites. Now in Year 3, we count 32 blooming plants spread across seven distinct sites, with many healthy seedlings and seeds coming on for the future. We set out a few plants each year to start new sites, but the overwhelming increase is the result of removing invasive species around the parent plants, and creating space for the native thistles to sow themselves and recover to sustainable numbers. This is inspiring progress.
Now, let's step back and consider the big picture ... thistles, people, hummingbirds, butterflies, bumblebees, caterpillars, aphids, ants, seeds; soil, sun and rain ... it's all fantastic, isn't it?
It's our great honor to play a part; to mingle, merge, and marry with these many other lives.