Sphagnum russowii growing on an uprooted tree in a dark wet valley in the western Cascades.
What are mosses? When we refer to mosses, in a general sense we are intending to mean the small little green fuzzy stuff that grows on logs, rocks, in our lawns and on our roofs. This term can accidentally incorporate such things as lichens, algae, and other small vascular plants which are not mosses in the strict sense. The taxonomic name for moss is bryophyte, which when used, carries a greater accuracy, pertaining to all non-vascular land plants.
Vascular systems in plants is a later derived trait that is shared among all the clades following bryophytes (in the diagram to the right). Bryophytes do not have vascular systems, meaning, they do not have specialized tissues to transport water and nutrients throughout the plant body. Instead, bryophytes depend entirely upon the environmental humidity to maintain internal hydration. When these plants experience drought, they will desiccate and shrivel. This however is not a damaging process but a mechanical response to conserve water. In this state, bryophytes significantly reduce all cellular function until the next rain event. When water returns to their leaf surfaces, mosses will rapidly rehydrate and resume cellular processes without any damage being done to the plant. This is called Poikilohydry. The video to the right shows this event.
Different types of Bryophytes
Within the division of Bryophyta, there are the Marchanchiophytes (liverworts) the Anthocerophytes (hornworts) and the Bryophytes (mosses). It is suggested that both bryophytes and anthocerophytes trace their lineages to marchantiophytes. The photo to the right shows one of the members of this phylum: Ricciocarpus natans.
Anthocerophytes look similar to marchntiophytes in that they both have a thalloid growth form, however they differ in their ability to hold CO2 in their tissues, contain no oil bodies, while most liverworts have many oil bodies, and their reproductive structures disperse cells differently. This is a small group of bryophytes consisting of about 100 species worldwide.
The phylum, bryophyta, is the largest group within the division, bryophyta with approximately 10,000 species. This group consists of peat mosses, lantern mosses, and all other 'true mosses' (bryopsida). The main differences between this group and hornworts and liverworts is that they are all 'leafy' meaning there is no thalloid form except in the first stage of germination, leaves are never lobed, they do not have 'underleaves', and the sporophytes have a stomata.
