Hesperolinon congestum (Flowering Plants)

Species Description

The Marin dwarf-flax is a small herbaceous annual of the flax family (Linaceae) with slender threadlike stems. It has rose to whitish flowers that bloom from May to June or July. The flowers have anthers—the pollen bearing part of the stamen—that are deep pink to purple, a feature that helps distinguish this species from the closely related California dwarf-flax (Hesperolinon californicum). It is endemic to serpentine soils in Marin, San Francisco, and San Mateo Counties.

Residential development, off-trail trampling, grazing, competition with non-native invasive species, and upgrading public utilities threaten the species throughout its range. In San Francisco County one population of the Marin western flax declined by over 93% in the Presidio, Golden Gate National Parks. Since that time, the population has rebounded, but with severe fluctuation. There are no obvious causes of the fluctuation, but the amount and timing of rainfall no doubt plays a roll. It was protected as a threatened species under the federal Endangered Species Act in 1995.

Despite its moniker, many of the extant colonies of this species are currently in San Mateo County, on Peninsula Watershed lands and San Mateo County Parkland. A new population was discovered in 2007 at a city park in Belmont, CA. A good place to see the species along existing trails is at Edgewood County Park in Redwood City, CA.

There are 26 occurrences documented for the Marin dwarf-flax. In Marin County historically there were 13 occurrences. As of this report, 9 are considered extant, 3 are considered in excellent condition, 5 in good condition, 1 in fair condition and 4 with the condition not given and it is not known if they are still extant. For San Francisco County 4 occurrences are documented, of these, only 1 population is considered extant, 2 are known to be extirpated, and 1 is possibly extirpated. For San Mateo County 10 occurrences are documented. One population is considered excellent; 4 are considered good; 3 are considered fair and 2 are extirpated. Therefore, from the historical 26 occurrences a possible 18 are still extant.

Conservation Action Item

Restore Dwarf-Flax habitat:
Volunteer with the Presidio Park Stewards

Of the 12 locations where Marin Dwarf-Flax currently resides, two of those are in the GGNP. The species is threatened by residential and recreational development as well as with competition with non-native invasive species. Efforts to restore the species are underway in the Presidio, where NPS biologists will be attempting to experimentally establish new populations this year. Help restore the plant community that will sustain a new population of Marin Dwarf-Flax.

Big Year Competitors have reported 5 sightings and taken 2 actions to help this species recover so far this year.

Trips

• CANCELED-Presidio Clarkia and Marin Dwarf-Flax Habitat Restoration
  Saturday, 05 Jun 2010, 09:00 - 12:00 Pacific Time (US & Canada)
• Secret Ridge, Endangered Wildflowers
  Thursday, 15 Apr 2010, 09:30 - 15:00 Pacific Time (US & Canada)
• Marin Dwarf-flax Blooming: in San Mateo County!?!
  Saturday, 19 Jun 2010, 09:00 - 12:00 Pacific Time (US & Canada)