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!
Nitrogen is necessary for all life—essential to growth and reproduction. So what’s a plant growing in a nitrogen-poor environment to do? English sundew (Drosera anglica) adapted by becoming a hunter, trapping and digesting insects. This perennial herb is in the sundew family (Droseraceae), a group of plants that have evolved these carnivorous traps. In English sundew, clusters of leaves arise at the soil level and the leaf blades bear long, glandular hairs tipped with mucilage that traps the insects. The mucilage is acidic and enzymatic and does not evaporate, thus appearing as innocent water droplets. Once the insect is trapped, the petiole (the part of the plant that joins the stalk to the leaf blade) folds over the insect. The insect dies from exhaustion or asphyxiation and the plant digests it through enzymes in the mucilage.
Although often seen in a vegetative state (just clusters of leaves), English sundew can be found in flower or with fruits from June through August. The flowering stem can be as long as 10 inches, and the arching end of the stem bears small white flowers. This species grows in montane coniferous forest in fens, a special type of peat-accumulating wetland that is primarily fed by mineral-rich ground or surface water (rather than rainwater). It is only found in fens that are wet all season and do not experience seasonal drought. In these fens, English sundew lives in the wettest part, sometimes on floating Sphagnum mats. Often there is little available nitrogen in fens, creating a challenge for the plants that grow there, which must adapt to survive.
In California, English sundew is at the limit of its southern distribution and is known from approximately 28 locations in Butte, Lassen, Nevada, Plumas, Shasta, and Siskiyou counties. As the name implies, it also occurs in England. In fact, it has a wide circumboreal distribution that encompasses Eurasia, Canada, Alaska, the northern United States and then high elevation western states. It also has a disjunct occurrence in the high elevations of Kauai, Hawaii, thought to have been brought by migrating birds from Alaska!
Why is such a widespread plant considered rare? In the CNPS Rare Plant Inventory, English sundew is ranked 2B.3 (rare, threatened, or endangered in California but more common elsewhere). This category helps protect plants that are rare at the limits of their distributions. According to NatureServe, this species is considered critically imperiled to vulnerable in eight U.S. states and three Canadian provinces. Most online observations of this plant are from UC Berkeley’s Sagehen Field Station north of Truckee, a location that requires permission to visit. However, guided tours do sometimes take place.
Threats and impacts that have been recorded for English sundew in California include trampling due to recreational activities, timber activities, trampling and grazing by deer and cattle, collecting, fire, and competition from non-native species. In general, English sundew would be threatened by any action that alters fen hydrology, microclimate, or moisture level, including drought due to climate change. Visit the Rare Plant Inventory to learn more about English sundew.
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.
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