Yesterday I traveled to Roanoke to meet with Dr. D.B. Poli, a botanist from Roanoke College. From there we headed out to New Castle, in Craig County, Virginia to look for living examples of lycopods. DB and I are working on a project related to fossil lycopod ecology, and we needed some modern examples for our experiments (more on this in a future post).
The Lycopodiophyta (clubmosses or ground pines) are among the earliest vascular plants, probably showing up in the Silurian. (The terms “moss” and “pine” in the common names are misnomers; lycopods are not closely related to either mosses or pines.) They were fairly common by the Devonian, and by the Carboniferous they were among the dominant terrestrial plants. Lepidodendron reached tree-like proportions (estimates range from 10-30 meters in height), exemplified by this large stump (now on exhibit at VMNH):
They began to fall on hard times in the Mesozoic, with most of the large forms disappearing. Lycopods are still around today, but they’re a pale reflection of their former glory. Even though lycopods are found globally, they are relatively rare, and all the surviving species are small understory or aquatic plants.
The particular lycopod we were after is Lycopodium
clavatum digitatum, which is widespread but rare in North America. Even with all the time I spent in the woods as a child I don’t recall ever having seen Lycopodium, but DB has discovered a large patch (probably over half an acre) in Craig County. Here’s DB standing in the patch; pretty much all the understory plants are Lycopodium:
Compare to these much larger Lepidodendron branches from the Carboniferous, which are part of the McLoughlin collection (there are also a number of ferns in this sample):
Lycopodium can spread laterally by means of a rhizome (an underground stem), which periodically sends new branches above the surface. This is visible in the linear distribution of the plants in areas where the patch is a little thinner:
Lycopods reproduce using spores, which are carried in a structure called a strobilus. Strobili look a little like gymnosperm cones (and are sometimes referred to as cones), but they’re a quite different structure. The Lycopodium at the Craig County site were in a variety of different developmental stages, and many of them had well-developed strobili. In the image below, the strobili on the left have already opened and begun releasing spores, while those in the middle of the image haven’t opened yet:
Again, here’s a Carboniferous strobilus for comparison (this time from the Boxley Beckley Quarry):
The first step in understanding the morphology of a fossil organism is to look at its modern relatives (when it has some). Having the opportunity to look at Lycopodium has really helped me in understanding some of the fossil plants in our collection, and we now have the plant samples we need for our physiological experiments.