Juniperus jackii

(Rehder) R.P.Adams ex Adams & Schwarzbach 2012

Common names

None are given. Traditionally the plant has not been distinguished from Juniperus communis and would generally be called dwarf juniper or mat juniper.

Taxonomic notes

Type: Siskiyou Mtns., on the road from Waldo, Oregon to Crescent City, CA, elev. 3000 ft. 1904.08.25, J.G. Jack & Alfred Rehder s.n. (lecto A [accessed 2023.02.18], designated by Farjon [2005]). This taxon was first regarded as a variant form of Juniperus communis with a distinctive association with ultramafic substrates, and is still often called J. communis L. var. jackii Rehder (1907). However, molecular analyses of both nrDNA and cpDNA markers have established that it is more similar to J. formosana of Taiwan than to any of the several varieties of J. communis, which led Adams and Schwarzbach (2012) to recognize it as a good species in its own right. It remains possible that further molecular analyses may return it to the J. communis fold, but currently the preponderance of evidence favors recognition at species rank.

Description

Dioecious shrubs, procumbent, to 20 cm tall. Bark thin, brown, exfoliating in strips. Leaves needle-like, in whorls of 3, ascending, curved, 7-9 × 1-2 mm, with a single white adaxial stomatal band 3-4 times as wide as the green margins; keeled abaxially, base jointed, not decurrent. Pollen cones not described. Seed cones when ripe dark blue, glaucous, subglobose, 7-9 mm long. Seeds 1(-2) per cone, 3-4 mm long. Pollen shed in spring (Adams 2014). See Juniperus communis for a key to distinguish J. jackii from J. communis; these are the only two needle-leaved junipers native within the range of J. jackii.

Distribution and Ecology

USA: California (northwestern), Oregon (southwestern and Cascade Mountains), Washington (Olympic Mountains). Occurs at 300 to 2590 m elevation on ultramafic and silicate ("lava", "granite") rocks (Adams 2014 and herbarium specimen collection notes on specimens identified by Adams). This species is primarily distinctive for its strong association with ultramafic rocks (often called serpentine) in the mountains of northwest California and southwest Oregon; very few plants do well on such substrates, although quite a few conifers do, notably Pinus jeffreyi in this area (Whittaker 1960).

Distribution of Juniperus jackii. Map prepared using data from GBIF, downloaded 2023.02.15, DOI is https://doi.org/10.15468/dl.dvcgy5. All collections represent geolocated preserved specimens with coordinate accuracy of at least 10,000 m. Only one sample per location is shown, usually the earliest collection record. Click on an icon for its GBIF occurrence ID number; see GBIF for further data on each observation.

The IUCN (accessed 2023.02.16) has not assessed the conservation status of this species, but since it has a wide distribution and occurs in many areas with little or no human impact, it would likely be assessed as "Least Concern".

Remarkable Specimens

No data as of 2023.02.18.

Ethnobotany

No known uses (Adams 2014), however it is possible that some native peoples within its range used this species for the same purposes as Juniperus communis; these were primarily medicinal.

Observations

See the collection records on iNaturalist, where it is called J. communis var. saxatilis (accessed 2023.02.18).

Remarks

The epithet honors J. G. Jack, collector of the type specimen.

Citations

Adams, Robert P. 2014. Junipers of the World: The Genus Juniperus. Fourth edition. Trafford Publishing.

Adams, R. P., and A. E. Schwarzbach. 2012. Taxonomy of Juniperus section Juniperus: sequence analysis of nrDNA and five cpDNA regions. Phytologia 94:280–298 (p. 292). Available: Biodiversity Heritage Library, accessed 2023.02.17.

Rehder. 1907. Mitt. Deutsch. Dendrol. Ges. (16):70. Available: Biodiversity Heritage Library, accessed 2023.02.18.

Whittaker, R. H. 1960. Vegetation of the Siskiyou mountains, Oregon and California. Ecological Monographs 30(3):279-338.

See also

CalFlora provides photos and specimen locations.