Phylogeny of Vascular Plants

Originally, weighted Morphological Traits have been used to group plants and propose evolutionary trees. This is based on the analysis of Phenotype rather than Genotype which is an obvious weakness.

Recently, improved methodologies have contributed to a better understanding of interrelationships among plants.

These are Cladistics and Molecular Biology.

In the past, Morphological Traits were hypothesized by scientists to be Ancestral or Derived (advanced).

Reproductive Traits like floral anatomy were given greater weight in grouping plants than other traits like stem anatomy.This can be called the Adaptive Hypothesis for taxonomic relationships (Niklas, 1997). This means that similarities and differences in these "Adaptive" traits had greater adaptive significance, and were thus more characteristic for different or related taxa. These analyses were somewhat skewed.

For instance, the presence of numerous flower parts and radial symmetry are considered to be ancestral traits. Consequently, plants with these traits would be put into one group while plants with different floral traits would be put in another. Further grouping could involve a reduction in the number of parts, wheteher they appear in multiples of 3, 4 or 5, wheter they are fused or not etc.

Part of Cladistic analysis is to look at a large number of traits independently, without weighting, to see if the same taxanomic associations occur.

Molecular Data, although Objective is not without its ambiguities and sources of errors. However, they are based on the Genome rather than the "Phenome". Boy am I good at creating terms or what!!!!!

Morphological data is still the only way to deal with Fossils. However, DNA has been extracted from some fossils but I do not have specific knowledge regarding the utility of this for taxonomy.

The data combined from all of the above will hopefully lead to a clearer phylogenetic picture. It is an unfortunate reality in Science that new methods like DNA analyses blow away "old" Science. Both are valuable.

General Conclusions regarding the
Phylogeny of Vascular Plants

Combined data indicate that Vascular Plants are

Monophyletic   (They have a common origin.)

They originated from the Chlorophyta (Charales & Coleochaete)

The origin of land plants probably occurred from a haploid algal life cycle in which there was interpolated an extended development of the sporophyte while it was in contact with the gametophyte.

Later steps would lead to a separation of the Gametophyte & the Sporophyte phases and the ascendency of the Sporophyte phase.

Simplified Phylogenetic Flow Chart

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