CNDDB News Blog

Picture a thistle. What do you see? Do you imagine the yellow star-thistle blanketing dry hillsides in the late summer? Or perhaps the bull thistle, with its fat magenta flower heads and spines on every surface?

We tend to think of thistles as noxious weeds, unwanted invaders, and eyesores. But did you know that California is also home to 19 species of beautiful native thistles, 7 of which are endemic to our state? They may be spiky and sharp, but they are an integral part of many California ecosystems, from ocean dunes to mountain peaks. Thistles also produce a lot of nectar which makes them an important food source for native bumblebees, butterflies, and other pollinators!

Most of the native plants we would call thistles fall into the genus Cirsium, in the Asteraceae family. Some species of Eryngium also have the common name “coyote thistle” as they have a spiky growth form and similar-looking flowers, but they’re actually in the carrot family (Apiaceae) instead of Asteraceae!

Of the 14 Cirsiums that are CNPS-listed as rare species, 4 are federally endangered and 1 is extinct. The one extinct thistle, known as the Lost Thistle (Cirsium praeteriens), was collected near Palo Alto by J. W. Congdon in 1897 and 1901 but it was never seen again.

CNDDB staff had the opportunity to accompany the CDFW drone team and Native Plant Program to look for the federally endangered Suisun thistle on CDFW lands in the Delta. There are only a few occurrences of the Suisun thistle, and it grows in salt marshes with thick vegetation that makes it difficult to thoroughly survey on foot. However, drones can fly overhead and thoroughly photograph a site from the air. More and more botanists are turning to drones to survey areas inaccessible to humans, and drone surveys in Hawaii even rediscovered a plant thought to be extinct. We flew drones over a known population as well as a nearby marsh with suitable habitat, to see if it is possible to use the drones to identify new Suisun thistle populations, or to monitor existing populations. The results of this survey are still being analyzed, but if successful it could be an exciting new tool for plant conservation in California.

If you’d like to learn more about these misunderstood plants, check out the Xerces Society’s native thistle guide for more information about the native thistles of North America and their conservation value.

As always, if you spot one of our rare native thistles, fill out an Online Field Survey Form and snap a photo for a chance for your picture to be featured as our Photo of the Month!

Photo caption: Top: Western thistle (Cirsium occidentale) flower head; Middle right: The federally endangered Suisun thistle (Cirsium hydrophilum var. hydrophilum) grows in Delta salt marshes; Bottom left: Brownie thistle (Cirsium quercetorum) in bloom; Bottom right: Native bumblebee pollinating a Brewer’s swamp thistle (Cirsium douglasii var. breweri) 
Photo credit: Top: Kristi Lazar; Middle right: Rachel Powell; Bottom left: Kristi Lazar; Bottom right: Katie Ferguson

Left: Orobanche parishii ssp. brachyloba (CRPR 4) by Katie Ferguson; Middle: Orobanche bulbosa, (common) by Kristi Lazar; Right: Orobanche fasciculata (common) by Katie Ferguson

These fascinating parasitic plants are always a treat to find in the wild with their alien-looking flower stalks emerging straight from the ground and no leaves to be seen.

The genus Orobanche is home to parasitic plants that lack chlorophyll, and therefore completely depend on their host plant for nutrition. Some species are only able to parasitize a single host species, while others can survive on a wide variety of hosts. If you spot one, be sure to note the other plant species growing nearby so you can identify potential hosts.

Orobanche are often referred to by their common name “broomrape” which comes from the English word broom (referring to the shrubby plants in the pea family that broomrapes often parasitize) and the Latin word “rapum” (which roughly translates to “tuber”). Although recent phylogenetic studies now place all broomrapes found in California into the genus Aphyllon, for now CNDDB still uses the former genus name Orobanche.

CNDDB currently tracks four species of Orobanche, including Orobanche parishii ssp. brachyloba (California Rare Plant Rank 4.2). O. parishii ssp. brachyloba is found in coastal bluff scrub and coastal dunes on the Channel Islands and southern coast of California, with its range slightly extending into Mexico. It is most commonly found near Isocoma menziesii, which is presumed to be the preferred host plant for this species. The few remaining mainland populations are highly threatened by coastal urban development; however it is found to be widespread on several of the Channel Islands. If you see O. parishii ssp. brachyloba or any other rare broomrapes in the wild, be sure to submit your observation with our CNDDB Online Field Survey Form!

Ardeidae is a family of wading birds that includes herons, egrets, and bitterns. These birds are often characterized by their long bills, necks, and legs. They forage predominantly on aquatic animals including amphibians, fish, crustaceans, and mollusks. Additionally, some birds can be found foraging for small mammals, reptiles, and insects in grassy fields.

When the breeding season arrives, most Ardeids, excluding bitterns, gather into colonies called rookeries or heronries. The males will begin nest building and displaying in attempt to attract a female. The birds will form monogamous pairs for the season and take turns incubating eggs, brooding chicks, and foraging. They can lay 2-7 eggs depending on the species. During feedings, nestlings compete for provisions brought in by the parents. In years when food is limited, competition among nestlings increases and can result in aggression and siblicide. Nestlings may also behave aggressively toward nestlings in adjacent nests.

One of our very own Environmental Scientists has been volunteering with the Audubon Canyon Ranch Heron and Egret Monitoring Project to assist in their effort to monitor Ardeid colonies in the Bay Area. At a snowy egret (SNEG, Egretta thula) and black-crowned night-heron (BCNH, Nycticorax nycticorax) rookery in a residential park in Fairfield, she monitors and records the heron behavior and nesting success on a weekly basis. The flexible branches of the nest trees and the high winds of Fairfield plus the aggressive nestling behavior result in numerous chicks falling from nests. The survivors get loaded into cat carriers by volunteers and are shuttled to International Bird Rescue in hopes that they will recover and return to the rookery next year.

California has seven native Ardeid species: great egret, snowy egret, great blue heron, black-crowned night-heron, green heron, American bittern, and least bittern. We have one naturalized species: the cattle egret, which is native to Africa. All these species, except for the green heron and cattle egret, are tracked by the CNDDB. Be sure to fill out an Online Field Survey Form if you come across a nest site!

Top Left: One of the many trees used by the Fairfield rookery. The white birds are the SNEG. For every SNEG in the photo, there is likely a black and white BCNH adult or brown and white BCNH juvenile present but blending in with the tree. Top Right: Closer image of SNEG. Bottom Left: Fledglings under one of the nest trees – 3 SNEG and 1 BCNH. BCNH are known to have a high tolerance for disturbance as is evident in the proximity of the rookery to homes, traffic, and park-goers. Bottom Right: BCNH fledgling on park sidewalk.