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Polemonium confertum and Polemonium viscosum have blue/purple flowers that are a magnificent, uplifting, eye-opening surprise on 12,000 foot alpine scree and tundra. Leaves are succulent-appearing, finely cut, on vertical stems, and (in a manner similar to Polemonium pulcherrimum) almost always quite numerous in comparison to the number of flowers.  The plant may have a sweet or a pungent, not-too-pleasant odor. 

Weber, Kartesz, and the 20th century Polemoniaceae expert, Verne Grant, indicate that P. confertum and P. viscosum are very similar and that the former is a Colorado endemic. My own examination of numerous plants in the western San Juans reveals that plants here have some characteristics that the experts attribute to P. confertum and some characteristics they attribute to P. viscosum.  The two species do hybridize and apparently we have an abundance of the hybrids.

Weber separates the two species as follows:

Polemonium confertum has a "corolla... twice as long as the calyx" versus little longer than the calyx for P. viscosum.

P. confertum is "light blue" versus "deep purple" for P. viscosum.

P. confertum is "widely flaring at the mouth" of the corolla versus "not strongly flaring at the mouth" for P. viscosum.

P. confertum has orange versus yellow anthers.

P. confertum is found on scree versus tundra. 

Verne Grant's, "Taxonomy of the Tufted Alpine and Subalpine Polemoniums" (Botanical Gazette, 1989) provides a key to the alpine Polemoniums:

P. confertum: Corolla pale blue-violet, broadly funnelform with a throat 10-15 mm wide; inflorescence globe-shaped; Colorado.

P. viscosum:  Corolla deep blue-violet, narrowly funnelform with a throat 5-10 mm wide; inflorescence fan-shaped.

The drawings that Grant provides in his "Taxonomy" article indicate a difference in the leaves of the two plants and these differences do appear in the photographs below. The drawings show the leaves of P. confertum larger, less crowded, and on a longer stem.

Weber and Grant shared information about the two species and, as a comparison of the above characteristics shows, they do agree somewhat.  But notice some differences:

Weber emphasizes the difference in the lengths of the corolla tube and the color of the pollen.  These two characteristics are not mentioned by Grant.  Weber and Grant also differ on the color of the corolla: Grant sees the plants differing from pale to deep blue/violet; Weber sees blue versus purple.  Finally, Grant uses the overall shape of the cluster of flowers (the inflorescence) as a key to separating the two species: P. confertum's inflorescence is globular; P. viscosum's is fan-shaped.

In Intermountain Flora, Cronquist states of Polemonium confertum, "The proper taxonomic status of these plants is dubious".

Welsh does not refer to P. confertum, but some of the characteristics that he assigns to P. viscosum are quite similar to those assigned to P. viscosum by Weber and Grant.

Polemonium confertum

Polemonium confertum

Polemonium confertum

Polemonium confertum (Dense Sky Pilot)
Polemoniaceae (Phlox Family)

Alpine.  Tundra, scree.  Summer.
Woods Lake Trail, July 15, 2010 and Placer Gulch, July 20, 2013.

The floral tubes in the first five photographs are much longer than the calyces and all flowers flare widely at their mouth.  On the basis of these characteristics, the plants would probably be considered P. confertum by Weber and Grant.  However, the colors are reversed from what Weber and Grant indicate, i.e., P. confertum should have lighter blue/violet corollas. Perhaps most plants in the western San Juans are hybrids.

When the plants go to seed, it becomes even more difficult (if even possible) to tell which is P. confertum and which P. viscosum.

In 1864 Asa Gray named P. confertum from collections made by Harbor and Hall on their famous mammoth Colorado collecting expedition of 1862.  "Confertum" is Latin for "crowded".

Polemonium confertum

Polemonium confertum

Polemonium confertum

Polemonium confertum

Polemonium confertum (Dense Sky Pilot)
Polemoniaceae (Phlox Family)

Alpine.  Tundra, scree.  Summer.
Woods Lake Trail, July 15, 2010.

 

Polemonium viscosum
Polemonium viscosum (Sticky Sky Pilot)
Polemoniaceae (Phlox Family)

Alpine.  Tundra, scree.  Summer.
Madden Peak, June 22, 2004.

Polemonium viscosum
Polemonium viscosum (Sticky Sky Pilot)
Polemoniaceae (Phlox Family)

Alpine.  Tundra, scree.  Summer.
Madden Peak, June 22, 2004.

P. viscosum was first collected near the headwaters of the Platte River by Thomas Nuttall on his 1834-1837 western wanderings; he named and described the plant in 1848.  "Viscosum" is Latin for "sticky".

Polemonium viscosum

Polemonium viscosum

 

Polemonium viscosum  (Sticky Sky Pilot)
Polemoniaceae (Phlox Family)

Alpine.  Tundra, scree.  Summer.
Columbia Basin, June 22, 2010.

Polemonium viscosum

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Polemonium confertum

Range map for Polemonium confertum

Range map for Polemonium viscosum