Henderson's Checkerbloom (Sidalcea hendersonii) Newly Discovered in Alaska

Sidalcea hendersonii.
Sidalcea hendersonii at Howard Bay, Tongass National Forest, August 1, 2005. The flowers are about and 1¾ inch wide. Photo by Ellen Anderson.

During rare plant surveys, Ellen Anderson, the Botanist for the Juneau Ranger District of the Tongass National Forest discovered Sidalcea hendersonii (Henderson’s checkerbloom) in the northern part of southeastern Alaska. This first observation of the rare Henderson’s checkerbloom was made on August 13, 2003. The site is located in an upper beach meadow at Howard Bay, on the southern tip of the Chilkat Peninsula. Sidalcea hendersonii is a relatively tall plant with large, showy magenta-colored flowers (Figure 1). It is a member of the mallow family, which includes cotton and hibiscus.

The plant was found at the beach meadow/forest ecotone in a lush tangle of vegetation dominated by geranium (Geranium erianthum), beach pea (Lathyrus palustris),and Nootka lupine (Lupinus nootkatensis). The adjacent forest edge is dominated by Sitka alder (Alnus viridis ssp. sinuata), Sitka spruce (Picea sitchensis), salmonberry(Rubus spectabilis), and cow parsnip(Heracleum lanatum).

Since she found only a single plant, the botanist took photographs and collected several flowers in various developmental stages as well as three representative leaves for identification purposes. Time did not allow for an extended search for more plants. However, she returned the next week to conduct more extensive surveys and discovered one smaller, non-flowering plant near the first plant.

These plants are a 750-mile northwestward range extension for Sidalcea hendersonii. Formerly, the plant’s known distribution extended from the south coast of British down to coastal Oregon. This find adds a new species and family (Malvaceae) to Alaska’s flora. Taxonomic experts verified the plant’s identity and the specimen are deposited in the University of Alaska Herbarium at Fairbanks. In addition, the find and surveys are documented in Forest Service rare plant databases and the new record for Alaska added to the USDA Plants database.

An additional survey was done on August 1, 2005 to relocate the original plants, assess the condition of the population and search more of the area for other Henderson’s checkerbloom plants. Ellen Anderson; Mary Stensvold, the Regional Botanist; and Cindy Lagoudakis of the Juneau Ranger District conducted this survey. Three flowering Sidalcea hendersonii were found at the site of the original two plants. The surveys extended about 270 yards north and 1350 yards south of the site along the beach meadow-forest ecotone, but no other Sidalcea were found.

The continued existence of the population is imperiled by natural factors. The area is being subjected to tectonic uplift and glacial rebound. Consequently, the Sidalcea habitat in the upper beach meadow is undergoing relatively rapid successional changes and evolving into forest. During the August 2005 visit, successional changes were obvious, and potentially affecting the Sidalcea hendersonii. A young Sitka spruce tree adjacent to the population had grown considerably during the time between the 2003 and 2005 visits, and was encroaching on the Henderson’s checkerbloom. The spruce was judiciously pruned.

Because of its rarity throughout its range, and single location on the Tongass National Forest, Sidalcea hendersonii is likely to be designated as an Alaska Region sensitive species. Future rare plant surveys will include searches for the checkerbloom, and hopefully result in discovering more populations of this photogenic addition to Alaska’s flora.