Within the bryophytes, liverworts are the geologically oldest group, sharing a fossil record with the oldest vascular plants (Rhyniophytes) in the Devonian era.
Mosses
Of the three phyla of bryophytes, greatest species diversity is found in the mosses, with up to fifteen thousand species recognized. A moss begins its life cycle when haploid spores, which are produced in the sporophyte capsule, land on a moist substrate and begin to germinate. From the one-celled spore a highly branched system of filaments, called the protonema, develops. Cell specialization occurs within the protonema to form a horizontal system of reddish-brown anchoring filaments and upright green filaments. Each protonema, which superficially resembles a filamentous alga, can spread over several centimeters to form a fuzzy green film over its substrate. As the protonema grows, some cells of the specialized green filaments form leafy buds that will ultimately form the adult gametophyte shoots. Numerous shoots typically develop from each protonema so that, in fact, a single spore can give rise to a whole clump of moss plants. Each leafy shoot continues to grow apically, producing leaves in spiral arrangement on an elongating stem. In many mosses the stem is differentiated into a central strand of thin-walled water-conducting cells, called hydroids, surrounded by a parenchymatous cortex and a thick-walled epidermis.
This is a free page. This page contains 189 words. This
article contains 1,910 words (approx. 6 pages at 300
words per page).
Read the rest of this Article with our Bryophytes Access Pass.
