Learning about mosses can be a challenge because most information on bryophytes exists within the scientific community. The botanical terminology with binomial nomenclature (scientific names for plant species) are derived from Greek and then “Latin-ized.” To the lay person these terms can be daunting when interpreting technical descriptions. Because of their diminutive size, bryophytes cannot always be identified with the naked eye or even a close-up loupe. To confirm species, it may be necessary to examine botanical characteristics under a microscope. Another major roadblock is that western horticultural practices historically have overlooked bryophytes as a viable plant choices, usually considering mosses as weeds.
This site attempts to bridge this information gap and presents mosses in a manner that we hope is understandable to a wider audience. It is a challenge to translate the scientific explanation of bryophyte reproduction into lay terms. It may require your repeated review to soak in all this detailed information and botanical terminology.
Unique characteristics of BRYOPHYTES (Bryophyta)
Mosses — Bryophyta
Liverworts — Marchantiophyta
Hornworts — Anthocerotophyta
Note: Like other vascular plants, all bryophytes use photosynthesis to make their own food from water and carbon dioxide. Sustenance is derived from rainwater, mist and dew as well as nutrients in dust particles.
Non-vascular plants – lacking the ability to transport water or nutrients through an internal system
No roots, instead rhizoids – filamentous, anchoring structures without absorptive qualities of roots
No cuticle (waxy substance coating leaves) – allowing leaves to completely absorb all water and nutrients through leaf surfaces
Leaves are generally only one cell layer thick
No flowers and, therefore, no seeds for reproduction
Alternate generations – Gametophytic stage and Sporophytic stage comprise reproductive cycle
Ability to also reproduce through fragmentation or vegetative propagules (gemmae–tiny green balls)
Produce phenolic and related compounds that deter herbivores
Produce their own “anti-freeze”
Acrocarpus mosses have sporophytes that grow from the top of the plant.
Pleurocarpus mosses have sporophytes that emerge from prostrate stems or branches.
Bryophytes reproduce through alternate generations which means they go through two main stages — gametes (plants with sexual organs) and sporophytes (spore-bearing plants). Bryophyte gametes start in the protenema stage of hairlike filaments forming a mat. It will grow into a plant with a stalk and leaves. Individual plants live in colonies which may include other bryophyte types, cryptogams or vascular plants. Plant colonies will have both male (antheridia) and female (archegonia) organs growing on the same plant (monoecious or bisexual) or nearby as a separate plants (dioecious or unisexual). Under moist conditions, the sperm produced by the male organ will swim to fertilize the egg produced by the female organ. Please refer to the diagrams provided courtesy of Dr. Michael Knee, The Ohio State University. Check out this video for more scientific details the life cycle of mosses-bryophytes.
The alternate generation begins as the fertilized egg develops during the sporophytic state of reproduction. At the base of the new plant, spores are created that move up through the tiny stem-like structure called a seta. The spores accumulate in the spore capsule (calyptra). When mature, the spores will be released all at once or in bursts prompted by the wind. Although other types contain far fewer spores to disperse, the capsule of a Polytrichum moss can hold up to one million spores. The incredible power of spores exploding is extraordinary as illustrated by this video produced by Dwight Whittaker and Joan Edwards in their research on vortex rings created from Sphagnum moss spore explosions. The spores dispersed at speeds of 65 miles per hour in a mushroom cloud that resembles a nuclear explosion.
Sometimes these setae are short or they could be tall depending on the bryophyte type. During this sporophytic stage, moss setae and spore capsules will display an array of brilliant colors – bronzes, golds, scarlets. The sporophytic stage, in some mosses, may be apparent for months as they mature. In contrast, liverworts are far less showy with clear or whitish setae and sporophytes that may last only a few days. In the case of Marchantia, a liverwort, it has a complex, umbrella-like structure for its spore capsules. Horns on hornworts are the equivalent of sporophytes.
Beyond this alternate generation process with gametophyte and sporophytes, bryophytes can reproduce through fragmentation and vegetative reproductive processes. These hardy little plants are determined to spread one way or another. Literally, fragments of plants can grow into new plants when moved by wind, water or birds/animals disturbing their habitats. Another absolutely amazing aspect of mosses is that fragments don’t have to land right side up. Mosses can grow from even the base or stems of moss fragments. Leucobryum (Pincushion moss) can grow into a ball or what I call a moss cookie with green growth on all sides if rotated. I’ve heard that moss balls roll across the moors of Ireland.
The vegetative reproductive process is a bit more complicated botanically. It involves the production of gemmaes, usually growing directly off stems and are visible only under a microscope. These tiny, green balls (propagules), which get their name from the Latin for “jewels,” are developed in cup-like structures. Gemmae balls can be dispersed to new locations and will grow into new gametophytes (bryophyte plants-1st stage).
Differences between Mosses and Liverworts
Mosses and liverworts may be confused by the casual “moss lover.” A forest with an expanse of green might actually be liverworts (thalloid-with big leaves). The other type of liverworts (leafy- with tiny leaves) adorn barks of trees and are usually so small that you would need a hand lens or microscope to see the distinctions. In fact, some of the differences between mosses and liverworts will need to be observed with a closer look through a microscope.
Please note: There are always exceptions to the rules.
Leaves spiral around stem Two alternating leaves across from each other, 3rd smaller one
Colorful sporophytes, capsules vary in shape Clear setae, Umbrella
Pointy leaves Round leaves
Midrib usually present in leaf No midrib
Rhizoids — multicellular Rhizoids — unicellular
No oil bodies Oil bodies present at cellular level