By Ellen Dean
The Rare Plant of the Month blog highlights one of the rare plants in the CNPS Rare Plant Inventory (RPI), an invaluable resource that has helped protect approximately 2,450 rare plant taxa in California since 1974!
Do you remember that Far Side comic on ways nature tells us to not touch? Some plants very definitely tell us not to even think about getting near! So in honor of spooky season, get to know a scary-looking, spiny, perennial herb that bites back if you touch it—desert mountain thistle (Cirsium arizonicum var. tenuisectum). With a California Rare Plant Rank of 1B.2 plant (rare and endangered in CA and elsewhere), desert mountain thistle is mainly known from the desert environments of San Bernardino County and adjacent Nevada where it grows in rocky washes in Joshua tree woodland, Mojavean desert scrub, and pinyon and juniper woodland.
Amazing leaf architecture is a hallmark of the Cirsium species, which are generally recognized by their lobed, spiny leaves and the many spiny bracts (phyllaries) that surround heads of long, tubular flowers. In the case of desert mountain thistle, the leaves and phyllaries can have very long spines that are painful to touch. Use gloves if you must get close!
Desert mountain thistle is in the daisy family (Asteraceae), which is one of the largest families of flowering plants with over 23,000 species worldwide. About 200 of those species belong to the genus Cirsium, and approximately 23 Cirsium species are present in California. When people think of this genus, they may think of non-native species that have invaded California, like bull thistle (Cirsium vulgare). However, only a few of the Cirsium that grow in California are non-natives—all the rest are important native food sources for native pollinators, who are not fazed by dangerous spines!
The dark pink flowers of Desert mountain thistle can be seen June through November. This plant is not particularly easy to meet, for which you may breathe a sigh of relief. It has most often been encountered in the canyons of the New York Mountains where the only threat it faces is recreational off-road vehicles. Learn more about desert mountain thistle in the CNPS Rare Plant Inventory.
Ellen Dean is Associate Rare Plant Botanist at CNPS, helping complete rare plant profiles. In a previous life, she was an herbarium botanist, performing plant IDs, leading collecting field trips, training students in plant identification, curating the herbarium, and publishing taxonomic papers.
