Western Jacob's-ladder Polemonium occidentale spp. lacustre

Flowers of western Jacob's ladder plant.
Flowers of western Jacob's ladder.

For botanist Bruce Carlson, discovering a new location of western Jacob's-ladder (Polemonium occidentale spp. lacustre) will surely rank among the best personal discoveries of a lifetime. The botanists, ecologists and zoologists of the Minnesota Biological Survey (MBS) spend countless hours hiking, crawling, climbing and wading through Minnesota's native plant communities and geologic features searching, in part, for rare plants and animals. Although most rare features are by their very nature difficult to find, rarities are nonetheless found every field season. However, western Jacob's-ladder is elusive. As Bruce recalls, "Some of the best field botanists in the country have searched thousands of acres for P. occidentale spp. lacustre with little success. Therefore, when I came upon the first vegetative shoots I was not immediately confident that I was looking at western Jacob's ladder. I thought, 'Um, looks like western Jacob's ladder...but it can't be...that's too rare for me to find. It surely must be an escaped cultivar or some sort of fern.' But then I looked across a small opening in the wet cedar forest and nearly fainted with amazement when I spotted a flowering stalk. A rush of adrenaline surged through my veins as I shouted to the heavens, 'Lord, I am not worthy, show me a sign if this is indeed the rare western Jacob's ladder!' The words had barely left my lips when my feet uncontrollably started dancing the releve jig, my belly rolled with amusement, and a smile formed on my face so big that I had to turn my head sideways in order to fit that grin between the trees as I hiked out of the forest!"

Western Jacob's-ladder (Polemonium occidentale ssp. lacustre) is a perennial plant with conspicuous sky-blue/bright violet flowers and ladder-like dissected leaves found in rich conifer swamps in northern Minnesota and Wisconsin. In fact, all six known locations of the subspecies worldwide are in these two states. Minnesotans can take pride in knowing that their home state contains four of those populations, while Wisconsinites can lay claim to the other two populations.

Western jacob's ladder plant.
Sixth location worldwide.

Closely related to Polemonium occidentale, a species common in the Rocky mountains, the subspecies located in Minnesota and Wisconsin was first discovered in 1944 in St. Louis County, Minnesota by Olga Lakela, then curator of the University of Minnesota at Duluth Herbarium and a noted authority of northern Minnesota flora. This discovery served as the basis for defining a new subspecies previously unknown to science. A subsequent collection was made by one of Lakela's students in 1946 somewhere near the original location, but the location of both these populations became somewhat of a mystery to Minnesota botanists, who searched unsuccessfully for the plant throughout the 1960s and 1970s. Because the population could not be found, some people discredited Lakela's discovery, claiming that she might have transplanted a garden variety western Jacob's-ladder, P. caeruleum, into the site; or even faked the collection. Because the species had been nominated for consideration for the federal endangered species list, the Minnesota Natural Heritage and Nongame Research Program initiated a search for the lost populations in 1988 and literally stumbled upon a population after two days of searching within a mile of the area described in Lakela's field notes. The 1946 location, however, has never been relocated and is not counted among the six known locations.

Meanwhile, in 1982, Polemonium occidentale ssp. lacustre was discovered by botanists working for the Nicolet National Forest. This was an interesting find because it is located in habitat similar to the Lakela site but it is over 200 miles to the east in Florence county, Wisconsin, near the border of the Upper Peninsula of Michigan. At that time the botanists who found the Florence population speculated that perhaps it originated from seeds brought into Wisconsin on the boots of forest fire fighters working between midwestern and western states, thus downplaying the subspecies' rarity.

Both the attempt to discredit Lakela and the dirty-boot hypothesis were laid to rest in 1989, when Wisconsin specimens were sent to Dr. Dieter Wilken, an authority on the genus, for verification. He determined the Great Lakes Polemonium to be a distinct subspecies, as well-differentiated from other members of the genus as they are from each other. Western Jacob's-ladder also differs from the garden species, P. caeruleum, in its lack of glands at the summit of the stem, its shallow, creeping rhizome, and its larger number of leaflets (9-13 as opposed to 3-7) in the leaf subtending the flowering stalk. Because P. occidentale ssp. lacustre was being considered for inclusion on the federal endangered species list, a concerted effort to locate new populations was conducted between 1992-95. Two professional botanists, working in Minnesota and Wisconsin, spent many weeks visiting 73 sites covering over 10,000 acres of habitat similar to the known locations. Despite these extensive searches and the efforts of other field botanists, only three more populations of the species were found between 1988 and 2001: two Minnesota sites 15 miles east and 50 miles south of the original location, and a second Wisconsin site, less than a mile from the first Wisconsin location. Another nine years passed when, in the summer of 2001, Bruce Carlson, a botanist and ecologist with MBS, located the fourth Minnesota location and the sixth worldwide location in a conifer swamp in southeastern Itasca county, approximately 30 miles from the nearest previously known Minnesota site.

Cedar swamp habitat of the western Jacob's ladder plant.
Cedar swamp habitat.

Typical habitat for western Jacob's-ladder is in a rather open wetland forest community with various amounts of white cedar (Thuja occidentalis), tamarack (Larix laricina) and black spruce (Picea mariana), and a continuous carpet of moss dominated by Sphagnum spp. Other interesting plants often associated with western Jacob's ladder include dragon's mouth (Arethusa bulbosa), showy lady's-slipper (Cypripedium reginae), cuckoo-flower (Cardamine pratensis var. palustris) and greater arrowgrass (Triglochin maritima). All of the known locations have a near neutral pH and water chemistry that suggests groundwater up-welling.

Two human activities that often occur in this type of native plant community are peat mining and logging. While peat mining would definitely destroy all plants within the mining area, winter logging appears to either have no affect on the species or may actually promote its growth. All of the known locations have a history of logging. In some cases the logging occurred during the early 1900s while other sites have a more recent logging history dating to the 1980s and 1990s. In all six known locations, P. occidentale ssp. lacustre is most abundant and only blooms abundantly in natural or logging-related open areas where direct sunlight reaches the ground layer. While the relationship between logging and western Jacob's-ladder has not been investigated it appears that winter logging under frozen ground conditions is not a serious threat to the persistence of this species.

Factors controlling the rarity of this species are not well understood. In fact, the species has many characteristics that suggest that it should be more common. For example, there are millions of acres of apparently suitable habitat; it is a conspicuous plant not easily overlooked even by amateur botanists; the known locations have hundreds to thousands of individuals; and there is a large gap with many acres of suitable habitat between the Minnesota and Wisconsin populations. Despite the immense acreage of potential habitat, this species has received more concentrated attention than the majority of rare species in the Upper Midwest. Yet, over the course of recent field seasons, these efforts produced very few additional locations. Clearly, Polemonium occidentale ssp. lacustre is a true rarity!

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