An Ode to Moss

From the beaches of the Pacific Ocean to the western slopes of the Cascade Mountains, from the redwoods of Northern California to lower British Columbia, the low-elevation bioregion known as Cascadia is host to the world’s most massive forests in terms of standing biomass.  Thanks to the bioregion’s temperate climate and annual precipitation that approaches 200 inches per year, old-growth redwoods and Douglas firs grow over 300 feet tall, and western cedars grow stout trunks over 10 feet thick.  Below the canopies of these massive conifers, however, is the often overlooked ground cover that we’d like to recognize and appreciate: bryophytes, also known as moss and liverworts.  Cascadia is home to the most diverse collection of moss flora anywhere in the world!

Bryophytes are unique in that they are non-vascular plants.  Flowering plants, conifers, and ferns all have well-developed systems to conduct water and food and enable growth; in contrast, the conducting tubes bryophytes use are poorly developed.  For the most part, being non-vascular means that bryophytes must grow in wet places that are close to the ground or on other wet hosts such as trees.

The leaves of both mosses and liverworts are typically only as thick as a single cell, and thus have a semi-transparent appearance.  With some 9,000 species of moss and 6,000 species of liverworts, both types of the species are globally common.  Liverworts are somewhat common in Cascadia, however the species is more commonly found in the Southern Hemisphere.  Liverworts also tend to have leaves that are pressed flat against their stem, and their capsules (reproductive organs) have less overt, truncated stalks.  In comparison, mosses grow relatively tall stalks with prominent capsules.

How important are bryophytes? Very.  Among other miscellaneous domestic uses (think peat moss), mosses are critical in replenishing an ecosystem’s acid and nitrogen levels.  So the next time you are out on the trail, look down and examine where you are standing; you might be surprised at the species variety you will find.