Rare Plant of the Month: Shasta maidenhair fern

 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!

Ferns predate flowering plants in the fossil record and first appeared on earth hundreds of millions of years ago. Shasta maidenhair fern (Adiantum shastense) is a rare perennial herb in the brake family—or maidenhair fern family—(Pteridaceae). The brake family has about 1,000 species worldwide, with 90 found in California. Many of the California species specialize in dry habitats, but not the maidenhair ferns! Maidenhair ferns are usually found in shady, moist habitats, and their genus name, Adiantum, is from the Greek “unwettable,” referring to the ability of the leaves to shed water. If you visit a waterfall in California, or see a cliff face dripping with water (such as the awe-inspiring Fern Canyon in Humboldt County), you will often see a species of maidenhair fern.

One of the interesting things about this species is that it was hiding in plain sight from the western botanists who explored Northern California for over 100 years. It was described as new to science and given a scientific name in 2015. Before that, botanists usually mistook it for the more common Adiantum jordanii. One important way that the two species differ is that Adiantum shastense has mature leaves that stay green through the summer and into winter, while those of Adiantum jordanii wither and die back in late spring or early summer and are no longer visible in late summer, fall, and early winter. In addition, the old leaves of Adiantum shastense tend to build up, and the old leaves can be seen underlying the new leaves in the spring.

Shasta maidenhair fern is one of a number of vascular plants endemic to (only found in) the region surrounding Shasta Lake. These include Shasta snow wreath, Shasta ageratina, Shasta limestone monkeyflower, Shasta fawn lily, Shasta huckleberry, Damnation Pass phacelia, and Minnesota Mountain onion! The reasons why these plants are all endemic to this small area may have to do with both the area’s geologic history and past and present climate, which allowed species to persist and diversify over time. You can find Shasta maidenhair fern along the many trails on the edges of Shasta Lake, including Bailey Cove Trail. Visit the Rare Plant Inventory to learn more about Shasta maidenhair fern.

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.