Key Group.

Green algae called charophytes

1. chloroplasts:  only green algae with betacarotene and chloroplast as accessory pigments, stacked thylakoids, very similar chloroplast DNA.

2. biochemistry:  have the most cellulose in the cell walls than any other, only algae with peroxisomes, enzyme composition similarity.

3. cell division:  nuclear envelope dissolves, spindles last until cytokinesis, component cooperation identical (actin, microtubules, vesicles).

4. similiar sperm ultrastructure

5. similar genes and rRNA

What implies Plants' Alternation of Generations is Analogous rather than homologous to that of Algae?

Modern charophytes lack an alternation of generations!  So if charophytes represent the link between algae and plants then plants and algae individually evolved similar processes; this is an example of convergent evolution.  So now what does a researcher do?  He looks at the Coleochaete.

What does a Coleochaete have that is of importance?

1. has a haploid thallus (body).
2. zygotes remain attached to parent unlike most algae.
3. sterile cells originating in the thallus envelope the each zygote.
4. zygote enlarges.
5. meiosis occurs in the zygote.
6. releases haploid spores.

One Reason for this delayed meiosis.

This creates more spores, maximizing its reproduction capabilities so that when there is a lack of water there is a higher likelihood of fertilization occurring.

Shallow water as an intermediate to Land-dwelling.

A lot of modern charophytes live in the shallow water of ponds and streams.  Perhaps Glaciation brought new droughts and floods helping to cause seasonal and long-term alterations to the water level forcing this adaptation.

Next:  "Plants:  Nonvascular."