Liverworts

Day 362: Scientists are driven to name things (via those pesky taxonomists, of course): to categorize, to distinguish, the better to understand where any given species fits into the grander scheme. To know that This and That are related gives us perspective from two angles, and so much the better if we also know they are related to Those. The morphological commonality here is obvious: This, That and Those all belong to the family "Th-," further divided into genus and species by "-is," "-at" and "-ose," and that method (superficial as it was) served us well for many years. Then came DNA analysis, and now our preconceptions are flying out the window at an astonishing rate. Observation of macroscopic and microscopic characteristics is proving to be insufficient. The liverwort shown above demonstrates my point.

There are two schools of thought regarding this Marchantia. Some will argue that it is M. polymorpha, a common pest in greenhouses and nurseries. Others will claim that it is M. alpestris, and may even cite as proof the fact that it lacks the black median line seen in its cousin. Yet another branch will defend it as a different variety (M. polymorpha var. alpestris) or subspecies (M. polymorpha ssp. montivagans). It's enough to drive you mad! To date, Santa Claus has declined my requests for a DNA sequencer and someone with the knowledge to run it, so given that my observations of this liverwort have both occurred in alpine locations where it is unlikely to have been imported from a lowland greenhouse, I'm calling it Marchantia alpestris, and I reserve the right to be wrong.

My Favourite Marchantians

Day 273: It is argued that Marchantia alpestris should be treated as a separate species from M. polymorpha, a notorious pest in greenhouses. The differences are subtle, but more importantly, M. alpestris does not form extensive monocultures where it occurs naturally. The spread of this liverwort is kept in check by mosses, lichens and the harsh environment surrounding it, a factor which confines it to the shadier and damper areas of the subalpine ecology. It colonizes in areas scarified by fire and may be abundant until such time as other bryophytes and vascular plants get a toe-hold, but for the most part, only survives en masse in the mats of moss along the margins of small streams and seeps. The "umbrellas" shown in this photo are the male reproductive structures (antheridia).

Marchantia Alpestris - A Liverwort

Day 269: By and large, liverworts are far less common than mosses and lichens, and thallose liverworts (those having a "leafy" structure) even less common. In fact, most of our local species closely resemble mosses, so separating them visually without a hand lens can be daunting. On the other hand, the thallose species sometimes look like lichens, and that factor was what drew my attention to this specimen. From a distance, I took it to be Peltigera venosa, but on closer inspection, the pores and gemma cups characteristic of Marchantia became obvious. Although difficult to see in this photo, just above center in the middle of the lobe and again in the center of the lobe to the left, these structures are evident, each cup containing several gemmae (the spore-bearing "eggs" of the species). "Liverwort!" I exulted to my botany partners, Joe and Sharon. "But that's as far as I'm willing to go."

At home, I turned to the only two field guides covering Pacific Northwest liverworts to any extent, certain that they'd be inadequate to the task. I got as far as genus: Marchantia. My specimen was considerably larger than Marchantia polymorpha (a common pest in greenhouses, and one of very few liverworts I can recognize in the field), so I referred it out to expert David Wagner, who identified it as Marchantia alpestris, a species which occurs at higher elevations.