Western Jacob's ladder (Polemonium occidentale)

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Western Jacob's ladder fact file

Western Jacob's ladder description

KingdomPlantae
PhylumTracheophyta
ClassMagnoliopsida
OrderSolanales
FamilyPolemoniaceae
GenusPolemonium (1)

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).

Size
Height: 20 - 100 cm (2)
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Western Jacob's ladder biology

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).

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Western Jacob's ladder range

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).

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Western Jacob's ladder habitat

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).

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Western Jacob's ladder status

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

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Western Jacob's ladder threats

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).

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Western Jacob's ladder conservation

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).

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Find out more

Find out more about the western Jacob’s ladder:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Herb
A small, non-woody, seed bearing plant in which all the aerial parts die back at the end of each growing season.
Inflorescence
The reproductive shoot of a plant, which bears a group or cluster of flowers.
Perennial
Plants that live for at least three seasons; after an initial period they produce flowers once a year.
Rhizome
An underground, horizontal plant stem that produces roots and shoots.
Steppe
A vast grassland plain, characterised by few trees and low rainfall.
Variety
In taxonomy, the science of classifying organisms, variety is the rank below subspecies. Members of a variety differ from others of the same species in relatively minor ways.
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References

  1. UNEP-WCMC (July, 2011)
    http://www.unep-wcmc.org/
  2. Electronic Atlas of the Plants of British Columbia - Western Jacob’s ladder (July, 2011)
    http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Polemonium%20occidentale%20ssp.%20occidentale
  3. Schmidt, L.J. (2003) Conservation Assessment for Polemonium occidentale v. lacustre Western Jacob’s Ladder. Eastern Region of the Forest Service Threatened and Endangered Species Program, Wisconsin. Available at:
    http://www.fs.fed.us/r9/wildlife/tes/ca-overview/docs/Plants/W%20Jacobs%20Ladder.pdf
  4. Cullina, W. (2000) New England Wildflower Society Guide to Growing and Propagating Wildflowers of the United States and Canada. Houghton Mifflin Harcourt, New York.
  5. Center for Plant Conservation - Western Jacob’s ladder (July, 2011)
    http://www.centerforplantconservation.org/collection/cpc_viewprofile.asp?CPCNum=3557
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Image credit

Western Jacob's ladder flower  
Western Jacob's ladder flower

© Janelle Bloomdale

Janelle Bloomdale
http://www.flickr.com/photos/7925937@N02/

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