Plant Phylogeny

[Benauld]

Hi,

Does anybody know anything about the first vascular plants to evolve (along the lines of Rhyniophytes[sp?], Cooksonia etc)?

Specifically, whether such species would have been "pre-adapted" to survive in a salty environment, that is whether they would have been salt tolerant halophytes, or whether this is a completely secondarily derived characteristic?

Also, whether vascular plants evolved directly from sea-weed type algae (hence the salt tolerance questions), or from fresh water algae?

Many Thanks in Advance!

 

[Walter L. Wagner]

Benauld:

Look to the haploid Liverworts and Mosses. Their haploid phase [just like fern haploids, etc.] grows 'flat' along the ground. However, their diploid phase grows upright [especially in the liverworts], to allow maximum dispersal distance of their spores, located at the tip of the upright diploid extension that grows out of the haploid [from the fertilized egg].

It is believed that the diploid phase is much hardier [tolerates light better, etc.], and over time certain types of 'liverwort ancestors' were selected that had ever hardier upright diploid phases. Eventually, those evolved into the most primitive of the vasculars, as vascularization developed in those diploid phases.

Because the liverworts and mosses grow in wet, shaded locales [with only scattered, indirect light to sustain photosynthesis, primarily, though some have become quite tolerant of direct light], it is believed that those were the early land conditions for the progenitors of the vasculars.