Primitive Land Plants:
Before we start in with today's class lets view some examples of mosses and liverworts....
For the first 500 MYA, life on earth was primarily aquatic- yet now we characterize vegetation as being predominately terrestrial. How did this transition occur?
As we have discussed in the last classes, the oceans were physically supportive of the first plants...
- water unlike air can support mass- thus not much supportive tissue was required of the algae,
- there is no shortage of water and nutrients though limited, are available . This is critical when you consider the the high water content that makes up the plant cell,
- although water absorbs light rapidly, it also absorbs potentially mutagenic UV,
- it can readily transport mobile gametes, and
- it maintains a relatively stable temperature-wise unlike the air ( consider temperature fluctuations between the seasons and even between night and day)
For plants to survive on land, the slow evolution of a great number of adaptations was required, all which obviously did not occur at once.
Based on morphological features, the assumption is made that the bryophytes were the first primitive plants to evolve on land.
Evolutionarily, where do the bryophytes come in?
A diagram indicating current understanding of cladistic relationships of the major lineages of green algae and land plants. Abbreviations as follows: Chloro. = Chlorophytes; Pleur. = Pleurophytes; Ulvo. = Ulvophytes; Charop. = Charophytes; Micromonad. = Micromonadophytes; Liv. = Liverworts; Horn. = Hornworts; Trach. = Tracheophytes. (Modified from Mishler, B. D. et al. (1994) Phylogenetic relationships of the "green algae: and "bryophytes." Ann. Missouri Bot. Gard. 81: 451-483.) from: http://www.science.siu.edu/bryophytes/class.html
In the next pages, we'll review:
Life cycles and features of the Bryophytes
