From five feet above cushions of moss look alike but down on my hands and knees I can see the intricacies of the inch tall moss. Carpets of moss are like miniature forests that provide habitat for other plants, insects, worms, frogs, fungus and other small mammals, but moss is vastly different from the trees in a forest.
Moss is a plant, however, the structure of moss varies from what we typically think of for a plant. A tree has xylem and phloem tubes that carry water and nutrients between the roots and leaves. These tubes characterize trees as vascular plants. Mosses don’t have xylem, phloem or any other tubes which makes them non-vascular plants (bryophytes).
The outer structure of moss is also different. Trees have roots, leaves, stems, flowers, fruit or seeds. Mosses have rhizoids, spores and leaf-like structures. Moss is only a few inches tall at most because it lacks the lignin-fortified tissue required to support tall plants.
Like roots, the rhizoids (small, branched filaments) anchor the moss to the substrate it is growing on, whether the north side of trees, rocks, soil or concrete. However, rhizoids don’t absorb water and nutrients like roots, they only anchor the moss.
Instead, the leaf-like structures absorb moisture. The “leaves” are only one cell thick and absorb rain water as it flows over the plant and as water droplets from dew or waterfalls land on the plant. Numerous plants create a carpet of moss which produces a spongy quality that enables all the plants to absorb and retain water.
Without a root system to spread out to obtain water, moss is limited to where there is sufficient moisture. Over 12,000 species of moss grow from Arctic regions to the tropics and from around hot springs to the bottom of lakes.
Moss needs sunlight to create food but it is often found on the north side of trees to avoid the intense sunlight that can dry it out. If a moss dries out it won’t die. A moss needs moisture to live but not survive. Some mosses can be dried out for up to 20 years and spring back to life once moisture is present.
Moisture is needed for mosses to reproduce. Reproduction is vastly different from trees with flowers, seeds and fruit. Mosses reproduce using spores like ferns and mushrooms. Spores are similar to seeds but they are single-celled and more primitive than a seed.
During certain times of the year, upon close inspection you can see the carpet of moss sprouting tiny stalks with little capsules on the end. These capsules often hold more than 50,000 spores each. When the spores are fully developed, the capsule opens and the spores are dispersed.
Like a seed, a spore has to land in the ideal location to germinate. However, some spores are viable for up to 40 years waiting for the right conditions.
Moss isn’t solely dependent on spores to spread. Moss can spread by sending out new shoots in the spring from last year’s plants or by fragmentation. If a piece of moss is broken off and moved by wind or water, a new plant can start from that piece if enough moisture is present.
In ideal conditions like on the rocks next to a waterfall or in the damp reaches of old-growth cedar groves, vast carpets of moss can form over time into intricate miniature forests that we just have to get down on our hands and knees to see.