It is a little strange that the only time of year during which most people adorn their homes with vibrant green foliage (and even bring a LARGE CONIFEROUS TREE indoors) is also the time when the world outside is at its least green. Actually, these phenomena are probably related: as days get shorter and colder, we bring the few remaining green-things inside as reminders of the spring to come. So, as we deck our halls with boughs of Holly, kiss under the Mistletoe and garnish our foyers with the iconic Tannenbaum, I thought I would write a little story on the botany of the holidays.

What makes a Conifer?

Yesterday I helped my brother with the perennial ordeal of picking out and setting up a Christmas tree. For him, this means choosing a specimen with an appropriately “traditional” bushy-conical shape and “good needle-retention.” For me, it is an opportunity to do some coniferous botanizing. There are few better places to compare a wide variety of native and exotic conifer species than at a Christmas tree market. It’s also virtually the only time of year when conifers get to have their sexual bits (the female parts, anyway) put on display and sold at exorbitant prices. One also has an unusual chance to count tree rings and compare the ages of many of different trees. Overall, from a botanist’s perspective, this is a field day.

Pollen cones of Loblolly Pine (Pinus taeda); source — Pollen cones of Loblolly Pine (*Pinus taeda);* source

Since cone-bearing trees so rarely get to be in the limelight, I think it’s only fair that we should take an opportunity to at least recognize some of the broadly different groups; and lucky for us, it’s a pretty easy. First off, what makes a member of the Pine order (Pinales [pine-ALE-eze])? This is the group of plants comprising all coniferous tress and shrubs currently alive on Earth. These plants, as their name suggests, have cones (or “strobili”) as reproductive structures.

Each tree will bear male pollen cones (usually small and quickly disintegrating) and female seed cones (usually larger, tougher and maturing over a longer period of time, sometimes over many years). These cones are really the best diagnostic for the group as a whole. You may think of conifers as having needles or scales instead of broad leaves, but many actually do have broad leaves, like those in the genera Nageia and Agathis, which occur in Oceania. You may also have learned, as I did, about trees being grouped as either coniferous or deciduous. If you did learn this dichotomy, please take a moment now to unlearn it, because it is both misleading and self-contradictory.

Did you unlearn it…? OK, we can continue

A very large deciduous tooth of Charcharocles megalodon; source — A very large deciduous tooth of *Charcharocles megalodon*; source

Deciduous simply refers to a structure that is periodically shed and then regrown (incidentally, most sharks have deciduous teeth, which is one reason why it is a lot cheaper to buy a shark-tooth necklace than a lion-tooth necklace). Although it is true that many cone-bearing plants are “ever-green” (ie. with non-deciduous leaves) there is a whole genus of conifers that do shed their leaves every winter, and you have probably even seen and ignored them because they didn’t fit into your inferior deciduous vs. coniferous model of tree classification; these are the Larches (genus Larix) a.k.a. the deciduous conifer! There are also plenty of examples of evergreen plants that are not cone-bearing, like most of the plants that we bring indoors over the holidays, including Holly and Mistletoe. These plants are neither deciduous nor coniferous.

In writing this, I realized that there are many, many more stories to be told about holiday plants. For example, did you know that Mistletoe is, in fact, a parasite…? How romantic. Anyway that’s another story. For now, you can leave this blog with the satisfaction of knowing what really makes a conifer a conifer: cones. As for the variation in cone shape, size and degree of fleshiness (yes, there are bright red, fleshy, squishy cones out there, so beware!), and why they look the way they do, that will have to wait for the next plant story.