News from IAB

The mission of the International Association of Bryologists (IAB), as a society, is to strengthen bryology by encouraging interactions among all persons interested in byophytes.

Wednesday, June 20, 2018

My resistance may be futile: “bryophytes” might indeed be bryophytes.

From Puttick et al 2018. Current Biology 28:1-13.

Paraphyletic “bryophytes” might indeed be monophyletic bryophytes. In a recent paper, lots of transcriptome data and different types of phylogenetic analyses reveal support for bryophyte monophyly: [[[green algae [[hornworts, [liverworts, mosses]] tracheophyta]]]. The paper is:
Puttick MN et al. 2018. The Interrelationships of Land Plants and the Nature of the Ancestral Embryophyte. Current Biology 28: 1-13.
This new paper provides a synthesis of many different types of data (transcriptomic amino-acids), various models and inference methods for a large sample of exemplars from algae and embryophytes (103 terminals). The main results obviously challenge the idea of a progressive elaboration of cells, biochemical pathways, and simple morphologies from an ancestor similar to liverworts towards the complex morphologies in mosses and early vascular plants. Rather it seems that the ancestral embryophyte was more complex than previously proposed, complex enough to prompt research on the possible re-interpretation of several early land plant fossils.
@E. De Luna

For the last 25 years I have been so comfortable with the idea that “bryophytes” are not monophyletic. I learned that mosses are sisters to vascular plants, then hornworts sisters to both, and liverworts are placed at the base of phylogeny of land plants. This is the phylogeny of Embryophytes presented at the Tree of Life web project web site as a summary of available knowledge ( accessed June 13, 2018).

That mosses, liverworts and hornworts were not a monophyletic group was a revolutionary change from the long held classification in high school and college textbooks in the 70´s and 80´s. Hornworts, liverworts, and mosses, commonly referred to as bryophytes, were traditionally classified as a single group, Bryophyta (Margulis & Schwartz 1988, Raven, Evert & Eichhorn 1986).

Some early phylogenetic analyses, for example Garbary et al (1993), placed the mosses, liverworts and hornworths as monophyletic. However, a caveat was that this grouping could be anomalous because many of the ultrastructure characters of the motile apparatus of male gametes can be functionally correlated. Although bryophytes are undoubtedly the most basal plants among the embryophytes, and the three groups of bryophytes certainly share similarities, there was increasing evidence that together they did not form a monophyletic group (Mishler and Churchill 1984, Bremer 1985, Kenrick and Crane 1991, Lewis et al 1997). What remained uncertain was whether liverworts or hornworts were the most basal lineage among terrestrial plants (Duff and Nickrent 1999). Some phylogenetic analyses identified the liverworts as the most basal lineage of land plants. 
From Bowman JL  et al 2017. Cell 171: 287-304 

During the previous years, most phylogenetic analyses were consistent with the paraphyletic nature of the three groups of bryophytes. Some analyses supported the placement of mosses as a sister group of the vascular plants (Polysporagiomorpha, sensu: Kenrick and Crane 1997). Comparable characteristics between mosses and vascular plants are the unbranched sporophyte with a single sporangium, stomata, the shape of the gametangia, especially the bottle-shaped archegonia, the cuticle, and the internal conducting cells (Mishler and Churchill 1984, Mishler, Lewis et al 1994). However, it seems now I have to reconsider at least that mosses and liverworts can not be rejected as sister groups. Hornworts might well also be included in a monophyletic triad, Bryophyta. 

For the upcoming years my resistance to accept bryophytes are monophyletic might be pointless, but for a different reason. After several cycles of so much data gathering and different phylogenetic analyses at hand, it is surprisingly evident that the phylogenetic relationships among the three bryophyte lineages is still one of the unsolved questions in the biology of land plants (Goffinet 2000, Mishler et al 1994, Shaw and Renzaglia 2004). Which alternative hypothesis will be selected with more data and more analyses? No way to tell that. 

Bremer K. 1985. Summary of green plant phylogeny and classification. Cladistics 1: 369-385. 
Duff R. J. & Nickrent D. L. 1999. Phylogenetic relationships of land plants using mitochondrial small- subunit rDNA sequences. Am. J. Bot. 86(3): 372–386. 
Garbary D. J., Renzaglia K. S. & Duckett J. G. 1993. The phylogeny of land plants: a cladistic analysis based on male gametogenesis. Pl. Syst. Evol. 188: 237-269. 
Goffinet B. 2000. Origin and phylogenetic relationships of the Bryophyta. En: Shaw A. J. y Goffinet B. (eds) Bryophyte Biology. Cambridge University Press. 124-149 p. 
Kenrick P. & Crane P. R. 1991. Water-conducting cells of early fossil land plants: Implications for the early evolution of tracheophytes. Bot. Gaz. 152: 335-345. 
Kenrick P. & Crane P. R. 1997. The origin and early diversification of land plants: a cladistic study. Smithsonian Institution Press, Washington. 
Lewis L. A., Mishler B. D. & Vilgalys R. 1997. Phylogenetic relationships of the liverworts (Hepaticae), a basal embryophyte lineage, inferred from nucleotide sequence data of the chloroplast gene rbcL. Mol. Phyl. Evol. 7:377–393. 
Margulis L. & Schwartz, V. 1988. Five Kingdoms: An illustrated guide to the phyla of life on earth. W. H. Freeman y Company, New York. 
 Mishler B.D. & Churchill S.P. 1984. A cladistic approach to the phylogeny of bryophytes. Brittonia 36: 406-424. 
Mishler B.D, Lewis L.A., Renzaglia K.S., Garbary D.J., Delwiche C.F., Zechman F.W., Kantz T. S. & Chapman R. L. 1994. Phylogenetic relationships of the green algae and bryophytes. Ann. Miss. Bot. Gard. 81: 451-483. 
 Raven P. H., Evert R. F. & Eichhorn S. E. 1986. Biology of Plants. Worth Publishers Inc., NY. 775 pp. 
 Renzaglia KS, Schuette S, Duff RJ, Ligrone R, Shaw AJ, et al. (2007) Bryophyte phylogeny: Advancing the molecular and morphological frontiers. The Bryologist: Vol. 110, No. 2 pp. 179–213.
Shaw J. & Renzaglia K. 2004. Phylogeny and diversification of Bryophytes. Am J. Bot. 91 (10): 1557-1581.

No comments:

Post a Comment