California Native Plant Society – Riverside/San Bernardino Chapter Newsletter

The Encelia

 

 

What the heck is a bryophyte?

 

By Chris Wagner, San Bernardino National Forest

 

You walk along a path, maybe with a group of wildflower enthusiasts and enjoy all the wonderful flowers of the season, not really paying attention to the very small green things growing along the path or along a wet area. You are vaguely aware of them but feel they are so mysterious or so beyond your ability to identify, that you just pass them by. You briefly call them ‘another moss’ and move on the pretty flowers.

Bryophytes are considered to be the most primitive division of true plants and include mosses, liverworts and hornworts. It is believed that beginning with liverworts, bryophytes evolved from green algae and all other plants evolved from them during the Devonian period 400 million years ago.

 

Bryophytes are considered “non-vascular plants” which means they do not contain a true vascular system such as xylem and phloem. Instead, the vascular tissue system is in a simpler form. Only mosses have a rudimentary vascular system similar to xylem and phloem.

 

These conducting cells that transport nutrients and water throughout the moss plants are called hydroids and leptoids. These cells are similar to xylem and phloem in that they resemble water-conducting tracheary elements except they lack specialized, lignin-containing wall thickenings. These cell walls are much thinner and yet very permeable to water and solutes.

 

There has even been talk that moss may be taken out of the “non-vascular” category and put into the “vascular plant” category. Since the hydroids and leptoids are so different from xylem and phloem, this most likely will not happen. They are unable to pull water and nutrients up from the ground at any significant distance.

 

Liverworts and mosses have been found in the fossil record dating as far back as the Paleozoic Era in the Devonian period. Their true lineage still remains uncertain since the fossil record is rather poor. They are, however, believed to have shared a common ancestry with the green algae.

 

Sexual reproduction is also very different in bryophytes than in vascular plants. Beginning with the spores, leafy plant structures form called gametophytes. From these gametophytes, sexual reproduction occurs between the separate male and female plants, but only when water is present. The swimming flagellic sperm swims to the ovum of the female gametophyte which then forms an egg. This cycle then switches to the alternative cycle forming a sporophyte which contains spores. The cycle then begins again. Many bryophytes also produce ‘gemmae’: tiny buds, discs or leaf fragments which spread the plants vegetatively

 

Bryophytes can dry out and go into a dormant stage when no moisture is available. This is possible because bryophytes contain oil bodies in their cell structures that allow them to retain their integrity.

 

Moss are considered the ‘true’ bryophytes ascending from the division Bryophyta. Liverworts ascend from Marchantiophyta and hornworts ascend from Anthocerophyta. There are about 14,000 species of mosses, (most living in tropical forests) and 25,000 species of bryophytes in the world today.

 

Mosses have various roles in ecosystems. Some can help decompose to break up dead logs while others are pioneer species on bare rock surfaces.  Mosses help to keep the soils moist and prevent soil erosion and provide shelter for insects and other small animals.  Moss is also used for nesting material by birds

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Aulocium, photo by Chris Wagner

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