Field of Science

Relationships between the Three Groups of Bryophytes

I got an email this week from a colleague about the state of the relationships among the three groups of bryophytes: Mosses,  Liverworts, and Hornworts.

The first questions to consider - Are they three separate lineages? OR One monophyletic lineage?
If they are three separate lineages, what order should they be placed in relative to tracheophytes (plants that have tracheids, a special type of xylem)?

Well it all depends on which data are used.

Data from sperm ultrastructure (Garbary et al. 1993) and DNA data from entire chloroplast genomes (Nishiyama et al. 2003) points to the three groups being part of a monophyletic lineage, as in the diagram on the right.

However all the other studies that I can think of support these three lineages as independent and as a grade diverging prior to the evolution of the tracheophytes.


This phylogenetic relationship was proposed based on morphology, physiology, and biochemistry data (Mishler & Churchill 1984). Then subsequently supported by molecular sequence data (Mishler et al. 1994).


 
Another alternative hypothesis was supported by sporophyte morphological data (Garbary & Renzaglia 1998) and cox3 mitochondrial sequence data (Malek et al. 1996).



So, I think that this could be presented to students as an active scientific example of different data giving conflicting signals. Often science is much messier than we explain to students. They could be presented with multiple alternative hypotheses for these relationships and have to discuss the different scenarios or perhaps the different types of data used for each. 


However, if I only wanted to present one phylogenetic relationship to my students I would go with this one, below. This relationship is supported by Qui et al. (2006), which uses molecular sequence data from the chloroplast, mitochondria and nucleus on over 100 taxa. Others may disagree, but this is the phylogeny that I would recommend using as our most current hypothesis for teaching students about relationships among the bryophytes.



References

Garbary, D. J., K. S. Renzaglia & J. G. Duckett. 1993. The phylogeny of land plants: A cladistic analysis based on male gametogenesis. Plant Systematics and Evolution 188: 237-269.

Garbary, D. J. & K. S. Renzaglia. 1998. Bryophyte phylogeny and the evolution of land plants: Evidence from development and ultrastructure. Pp. 45-63 in J. W. Bates, N. W. Ashton & J. G. Duckett (Editors), Bryology for the Twenty-first Century. Maney Publishing, Leeds.

Kenrick, P. & P. R. Crane. 1997. The Origin and Early Diversification of Land Plants. Smithsonian Institution Press, Washington, D.C.

Malek, O., K. L├Ąttig, R. Hiesel, A. Brennicke & V. Knoop. 1996. RNA editing in bryophytes and a molecular phylogeny of land plants. The European Molecular Biology Organization Journal 15: 1403-1411.

Mishler, B. D. & S. P. Churchill. 1984. A cladistic approach to the phylogeny of "bryophytes." Brittonia 36:406-424.

Mishler, B. D., L. A. Lewis, M. A. Buchheim, K. S. Renzaglia, D. L. Garbary, C. F. Delwiche, F. W. Zechman, T. S. Kantz & R. L. Chapman. 1994. Phylogenetic relationships of the “green algae” and “bryophytes”. Annals of the Missouri Botanical Garden 81: 451-483.

Nishiyama, T., P. G. Wolf, M. Kughita, R. B. Sinclair, M. Sugita, C. Sugiura, T. Wakasugi, K. Yamada, K. Yoshinaga, K. Yamaguchi, K. Euda & M. Hasebe. 2004. Chloroplast phylogeny indicates that bryophytes are monophyletic. Molecular Biology and Evolution 21: 1813-1819.

What kind of Scientist are You?

I spent the past couple of weeks helping a friend move across the country. While on our travels I read this post from one of the professors in my department at the University of Connecticut. The idea is that you can identify what type of scientist you are in a personality-test fashion, based on whether you are Theory- or Data-Driven and a Nerd or Adventurer. 

The four types of scientists are listed below and are defined here by Virginia Hughes.

The Data-Driven Nerd
The Theory-Driven Nerd
The Data-Driven Adventurer
The Theory-Driven Adventurer

This stimulated some fun discussions while passing the time on the drive. I am definitely a Data-Driven Nerd. The part of science that I enjoy the most is running experiments in the lab. Though I do like adventure I usually get my fix through vacation travel on my time off, not directly through my research. And writing up my experiments for publication is my least favorite part of the process. My friend on the other hand is a Theory-Driven Adventurer. She is a political geographer who does her research in southeast Asia. I went to visit her last year while she was in Malaysia. A vacation adventure for me. 

I thought that this was a fun way to think about ourselves as scientists and what drives our interest in the questions that we ask. And I wanted to spread the word.

What kind of scientist are you?

Another Moss Misnomer

I am always on the lookout for plants called mosses that are actually not. I visited the Missouri Botanical Garden with some friends while in St. Louis a few weeks back for the Botany 2011 conference.  There I spotted this plant labeled Moss Fern. It is Selaginella pallescens, which is a lycopod or more traditionally called a fern ally. It is distantly related to moss as they are both green plants, but is definitely not a true moss. It has both vasculature (internal plumbing of xylem and phloem) as well as true roots to anchor it into the soil and function in water uptake.

There is a lot of plant life going on in this photo. The Selaginella is located behind the sign-post and also directly to the left. A few other species made it into the shot including a palm in the upper left and some mosses in the lower left.

There were quite a few other spots around the garden where mosses were growing, however, none of them were labeled. It is a bit of a bummer that the mosses are so blatantly ignored at a botanical garden. Here are a few shots from mosses inside the Climatron.

 

 
In general the garden didn't seem to add any fake animals to add to the tropical ambiance, thus this frog below looked a little out of place.

Some additional photos of the garden plants and me constantly looking for mosses can be seen over at my friend Em's blog