Juniperus zanonii

R.P.Adams (2010)

Common names

Zanoni juniper, Cerro Potosi juniper.

Taxonomic notes

Type: Mexico, Nuevo León, Cerro Potosí, elevation 3550 m, J. A. McDonald 1820, 1985.07.26. (Holotype TEX, though a search of their database reveals no record of this specimen). Synonymy: see POWO. Plants in this species were formerly assigned to J. monticola f. compacta on morphological grounds, but molecular analyses revealed it to be a new taxon, sister to the comparably-rare J. saltillensis but sufficiently distinct to warrant species or subspecies rank; Adams et al. (2010) chose the former. J. zanonii belongs to Juniperus section Sabina, within the very large clade of serrate-leaved junipers.

Description

Dioecious evergreen decumbent shrubs less than 1 m tall, the trunk branching at the base. Bark brown, divided into narrow strips. Leaves both whip-like and scale-like, margins denticulate, bearing a resin gland, the foliage very densely compacted. Pollen cones not described. Seed cones globose, 5-8 mm diameter, dark blue, glaucous, with a soft fleshy pulp and 2-5 seeds per cone. Seeds not described (Adams 2014).

Morphologically J. zanonii is very similar to J. monticola f. compacta. However, the 3-5 mm diameter twigs are rough in J. zanonii but smooth in J. monticola. The beak of the scale leaves is often ridged on J. zanonii but is domed and not ridged in J. monticola. The scale leaf glands, when visible, are oval and flat or raised on J. zanonii, but are elongated and sunken into a groove in J. monticola; the whip leaf glands are similar. Finally, J. zanonii is on limestone at timberline with Pinus culminicola and P. hartwegii, but J. monticola is on volcanic rock above the timberline (Adams 2014).

Distribution and Ecology

Alpine areas of Mexico: Nuevo León and closely adjoining parts of Coahuila and Tamaulipas, including Cerro Potosi, Sierra La Viga, Sierra La Marta, and Sierra Peña Nevada; not yet described but likely also occurring in Sierra Potrero de Abrego, Sierra Coahuilon, and Sierra Borrado. Grows on limestone-derived soils in association with Pinus culminicola and P. hartwegii near the alpine timberline; this is likely a relict distribution for a species that was much more widespread at lower elevations during the Pleistocene glacial maxima (Adams 2014).

The IUCN has not evaluated the conservation status of this species. Although it has a very small area of occurrence, no threats have been identified; however climate change risks have not been evaluated, and there is really no place it can go to in the event of climatic warming.

Remarkable Specimens

No data as of 2025.01.14.

Ethnobotany

In view of its small size and cold, distant habitat, J. zanonii likely has no uses other than as an ornamental, and so far I have not heard of any plants having been seen except in habitat.

Observations

Easily seen on Cerro Potosi, the summit of which is accessible by a reasonably good dirt road.

Remarks

The epithet honors Tom Zanoni, Adams's first Ph.D. student and now a noted botanist in his own right; amongst the gymnosperms, he has a particularly extensive publication record with the New World cycads.

Citations

Adams, Robert P. 2014. Junipers of the World: The Genus Juniperus. Fourth edition. Trafford Publishing. Brief versions of the descriptions are available online at Adam's website, www.juniperus.org.

Adams, Robert P., Andrea E. Schwarzbach, and Julie A. Morris. 2010. Juniperus zanonii, a new species from Cerro Potosi, Nuevo Leon, Mexico. Phytologia 92(1):105-117.

See also