Juniperus jackii
None are given. Traditionally the plant has not been distinguished from Juniperus communis and would generally be called dwarf juniper or mat juniper.
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.
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.
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).
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".
No data as of 2023.02.18.
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.
See the collection records on iNaturalist, where it is called J. communis var. saxatilis (accessed 2023.02.18).
The epithet honors J. G. Jack, collector of the type specimen.
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.
CalFlora provides photos and specimen locations.
Last Modified 2023-02-26