Each year, the Washington Rare Plant Care and Conservation Program (Rare Care) designates a handful of species as focus species – species that we are attempting to monitor all known populations on public lands within a three to five year period. This year, we added snow cinquefoil (Potentilla nivea) to our list of focus species.
In Washington, snow cinquefoil is a relic of a much colder period, when glaciers covered the northern part of the state. As glaciers receded, snow cinquefoil retreated north, following the toe of the glacier and colonizing the newly exposed soils. Today, snow cinquefoil only persists in Washington on alpine ridges and fellfields in Okanogan County.
This past summer several Rare Care volunteers relocated a healthy population during the monitoring weekend near Tiffany Mountain. Unfortunately, we searched unsuccessfully for four other populations, leaving us to wonder if this species is declining due to climate change.
Washington Natural Heritage Program (WNHP) tracks 20 populations of snow cinquefoil, all located at sites above elevation 7,000 feet. Only one of these sites has updated information in WNHP records; available population data on the other sites are over 20 years old. Review of herbarium records revealed only four specimens collected in the state in that time. The dearth of information provides little insight into how this species is responding to climate change. Our goal is to revisit all populations, which are all on public lands, to understand its current status.
Snow cinquefoil is a small, herbaceous perennial with compound leaves. Its leaves are mostly basal with three elliptic to oblong toothed leaflets that are greenish above and whitish below due to dense woolly hairs. Inflorescences typically hold clusters of one to nine stalked yellow flowers. It is distinguished from other closely related 3-leaflet cinquefoils by the number of teeth on the leaflets, number of flowers per inflorescence, and hairs on the low surfaces of the leaflets and the petioles.
Snow cinquefoil occurs from New Mexico north into Canada and to Alaska. Its range extends through northern Canada and east through northern Europe to eastern Asia. It is part of a complex of several species whose taxonomy is not yet resolved. Taxonomy is often tricky with apomictic species. These species do not require fertilization to produce viable seeds, and may include populations of mixed apomictic and sexually reproducing plants. Dandelions are an all too familiar example of this reproductive strategy.
In apomictic plants, seeds form from the maternal tissues of the ovule, leading to embryo development. The origin of apomictic reproduction is not well understood, but hybridization and the formation of polyploidy are thought to play a crucial role.
Apomictic plants typically have larger distributions than their sexually-reproducing relatives, tend to range to higher latitudes and altitudes, and tend to colonize previously glaciated areas. The term “geographical parthenogenesis” is used to describe this phenomenon. Asexual reproduction is advantageous in alpine areas where pollinators may be infrequent or absent and the growing season short. It can also be advantageous for colonizers because the absence of mating partners does not prevent reproduction.
Interestingly, apomictic individuals can cross with sexually reproducing individuals, producing offspring capable of apomixis. This can eventually result in populations solely comprised of apomictic plants. This is common at populations at the edge of a species range such as those of snow cinquefoil in Washington. Over time, the apomictic populations become genetically diverse as mutations originating in individuals within the population are passed to their offspring. Over large ranges, the accumulation of mutations and resulting diversification has led some botanists to classify these plants as separate species, and recent genetic sequencing tools are starting to shed a light on these relationships.
We know very little about the Washington populations of snow cinquefoil but hope our focus over the next few years will provide some insight. We added this species to the Miller Seed Vault in 2018, and hope we will be able to make more collections in the coming year.