Identifying an Alligator Juniper to variety

I went for a walk around a park near my apartment today. After being indoors cooking and eating all day yesterday, a nice long walk on a cold winter day was absolutely perfect.  I was planning to do some work on my grad school applications when I got back, but ended up identifying the plants along the walk instead.  I’ll make up for it by adding ‘compulsive botanizer’ to my CV.

The first thing I identified was an alligator juniper.  Most junipers have very distinctive scale-like leaves that pretty much cover the twigs.  The drawings below show fruit and scales of the four Juniperus species found in the Southwest. [UPDATE FOR NITPICKY BOTANISTS: Gymnosperms like junipers don’t actually have fruit in the botanical sense.  Instead of the ‘berry’ being derived from ovary tissue, juniper berries are female seed cones that have merged fleshy scales.]

Drawings of fruit and leaves of 4 juniper species

Drawings of fruit and scales of four Juniperus species, cobbled together from The Arbor Day website

Juniper scales and fruit look pretty similar between species and their weird little scale leaves make them jump out at you.  As most botanists will tell you, the easier it is to identify something to genus, the harder it is to get it to species.  Most botanists will also tell you that the exception is the rule.  The junipers in the southwest aren’t actually hard to tell apart once you know what to look for.  I like to start with the bark.

Alligator juniper bark - square pattern

Alligator juniper bark

The bark on alligator juniper (Juniperus deppeana) gives the game away.  This tree is actually named for its resemblance to alligator hide.  That was almost too easy, so lets keep going and identify this Juniper to subspecies variety; J. deppeana has five.  From Wikipedia:

  • Juniperus deppeana var. deppeana. Throughout the range of the species. Foliage dull gray-green with a transparent or yellowish resin spot on each leaf; cones 7-12 mm diameter.
  • Juniperus deppeana var. pachyphlaea (syn. J. pachyphlaea). Arizona, New Mexico, northernmost Mexico. Foliage strongly glaucous with a white resin spot on each leaf; cones 7-12 mm diameter.
  • Juniperus deppeana var. robusta (syn. J. deppeana var. patoniana). Northwestern Mexico. Cones larger, 10-15 mm diameter.
  • Juniperus deppeana var. sperryi. Western Texas, very rare. Bark furrowed, not square-cracked, branchlets pendulous; possibly a hybrid with Juniperus flaccida.
  • Juniperus deppeana var. zacatecensis. Zacatecas. Cones large, 10-15 mm diameter.

At first glance we can knock robusta off the list – I wasn’t anywhere near Mexico, or a climate like Northwestern Mexico.  We can eliminate sperryi for reasons of geography and the difference in the bark.  I didn’t notice any cones, so we can’t use the cone size to distinguish between pachyphlaea or deppeana and zacatecensis. Even if I had seen cones, there’s a bit of overlap in size that could make the comparison a bit dicey. I didn’t carry a ruler with me anyway.

But looking at the scales makes it very clear that this is pachyphlaea.

Juniperus deppeana var. pachyphlaea foliage

Juniperus deppeana var. pachyphlaea foliage with white resin spots on each leaf

The foliage is super waxy (glaucous) and there’s a spot of resin on every single little scale.  That means it could be deppeana or pachyphlaea, but since the resin is a brilliant white, not yellowish or transparent, we can call it pachyphlaea with certainty. 

There was another kind of juniper on my walk totally infested with mistletoe, but you’ll have to wait another few days to see that one!