Western Jacob's ladder  (Polemonium occidentale)

Western Jacob's ladder has not yet been assessed by the IUCN.

The western Jacob’s ladder (Polemonium occidentale) is a perennial herb of North America, named for the structure of its leaves, which are arranged in a ladder-like manner (3). The leaves are lance-shaped, hairless, and green to yellow-green, with a waxy blue powder on the lower surface. Each leaf measures around 1 to 3.5 centimetres in length. The blue, bell-shaped flowers are crowded in an elongate, fairly open cluster known as an inflorescence (2) (3).

The western Jacob’s ladder ranges mainly from Alaska, south to California and as far east as Idaho (4). A rare variety, Polemonium occidentale var. lacustre, occurs only in Minnesota and Wisconsin (5).

The western Jacob’s ladder is generally found in wet bogs and meadows at low to moderate elevations (4) (5). It may also occur along stream banks, in thickets in steppe areas, and in open forested areas with northern white cedar (Thuja occidentalis), tamarack (Larix laricina), black spruce (Picea mariana), and a ground cover of Sphagnum species (2) (3).

Little is known about the biology of the western Jacob’s ladder. However, it is a perennial species that flowers in late June and July, with a peak in flowering in early July. This species can reproduce from tiny seeds borne in capsules, which open after drying out, or can spread from short, unbranched rhizomes (3).

The western Jacob’s ladder is potentially at risk from any activities that destroy or degrade its habitat, especially in Minnesota and Wisconsin, where just five populations of the rare variety Polemonium occidentale var. lacustre exist (5). Threats to this species include peat mining, increased canopy closure and flooding caused by beaver (Castor canadensis) dams (3) (5). Overgrazing by deer may also be a problem where deer abundance is particularly high (3).

Polemonium occidentale var. lacustre is listed as ‘Endangered’ in both Minnesota and Wisconsin (5). All populations of this variety occur on public land, which is subject to restrictive uses, including timber production (3).

Find out more about the western Jacob’s ladder:

• Center for Plant Conservation - Western Jacob’s ladder:
  http://www.centerforplantconservation.org/collection/cpc_viewprofile.asp?CPCNum=3557