Briologia en Linea

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4. Clasificación de las briofitas

Las hepáticas, los antocerotes y los musgos son comúnmente referidos como briofitas, aunque estos juntos no constituyen un grupo taxonómico formal.

Los musgos, hepáticas y antoceros tradicionalmente se clasifican como un solo grupo, División Bryophyta (Margulis y Schwartz 1988, Raven, Evert y Eichhorn 1986).

Los tres grupos son un conjunto morfológicamente muy similar, pero no forman un grupo monofilético, aunque sin duda son los más basales entre las embriofitas. Los resultados de Garbary et al (1993) colocaron a los musgos, hepáticas y antoceros como monofiléticos. Sin embargo, ellos sugirieron que esta agrupación podría ser anómala debido a que muchos de los caracteres de ultraestructura del aparato motil de los gametos masculinos pueden estar funcionalmente correlacionados.

Los tres grupos de briofitas ciertamente comparten similitudes, pero hay evidencia en aumento de que juntos no forman un grupo monofilético (Mishler y Churchill 1984, Bremer 1985, Kenrick y Crane 1991, Lewis et al 1997).

Análisis recientes son consistentes con la naturaleza parafilética de los tres grupos de briofitas y la colocación de los musgos como hermanos de las plantas vasculares (Polysporagiomorpha, sensu Kenrick y Crane 1997). Aun es incierto si las hepáticas o los antoceros son el linaje mas basal entre las plantas terrestres (Duff y Nickrent 1999). Algunos análisis filogenéticos han mostrado que los musgos están más relacionados con las plantas vasculares que con las otros dos grupos de briofitas.

Hepáticas

Antoceros

Musgos

El esporofito no ramificado y con un solo esporangio de los musgos es comparable con los esporofitos ramificados y con tres esporangios en Horneophython y Aglaophyton (Rhynia) major.

Otras características comparables entre los musgos y las plantas vasculares son los estomas, la forma de los gametangios, especialmente los arquegonios en forma de botella, la cutícula, y las células conductoras internas (Mishler and Churchill 1984, Mishler, Lewis et al 1994).

Las relaciones filogenéticas entre los tres linajes de briofitas permanece como una de las grandes preguntas sin resolver en la biología evolutiva de las plantas (Goffinet 2000, Mishler et al 1994, Shaw y Renzaglia 2004).

REFERENCIAS

Bremer K. 1985. Summary of green plant phylogeny and classification. Cladistics 1: 369-385.

Duff R. J. y 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. y 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. y 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. y 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. y 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. y 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. y 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. y 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. y 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.

Abstract. Revolutionary new concepts of bryophyte relationships have emerged from molecular phylogenetic analyses conducted since the onset of the 21st century. For example, sequence data contradict the historical notion that isophylly in leafy liverworts is plesiomorphic and that simple thalloid liverworts are monophyletic. Also contrary to traditional views are the concepts that Leiosporoceros is genetically distinct from other hornworts and that Oedipodium is sister to the peristomate mosses. Substantial increases in ultrastructural and anatomical data likewise have provided new insights on interrelationships. Because of this recent deluge in evolutionary studies on bryophytes, it is an opportune time to co-examine contemporary morphological knowledge and novel molecular hypotheses. An understanding of bryophyte evolution and biology is essential to identify structural innovations that accompanied early land colonization and to illuminate the evolution of more complicated body plans in tracheophytes. In this review, we examine the progress that has been made since the 1999 International Botanical Congress in clarifying the evolutionary history of the three groups of bryophytes. The state of our knowledge on interrelationships is discussed, with poorly-known, genetically divergent taxa illustrated for each group. Our review of bryophyte evolution includes a reëvaluation of the evolution of sperm cells, sporogenesis, stomata, symbioses, conducting cells and chloroplast ultrastructure in hornworts. We explore the prospects for future discoveries and advances with an emphasis on fundamental evolutionary problems that remain and the challenges that must be met to resolve them.

Shaw J. y Renzaglia K. 2004. Phylogeny and diversification of Bryophytes. Am J. Bot. 91 (10): 1557-1581.

Abstract. The bryophytes comprise three phyla of embryophytes that are well established to occupy the first nodes among extant lineages in the land-plant tree of life. The three bryophyte groups (hornworts, liverworts, mosses) may not form a monophyletic clade, but they share life history features including dominant free-living gametophytes and matrotrophic monosporangiate sporophytes. Because of their unique vegetative and reproductive innovations and their critical position in embryophyte phylogeny, studies of bryophytes are crucial to understanding the evolution of land plant morphology and genomes. This review focuses on phylogenetic relationships within each of the three divisions of bryophytes and relates morphological diversity to new insights about those relationships. Most previous work has been on the mosses, but progress on understanding the phylogeny of hornworts and liverworts is advancing at a rapid pace. Multilocus multigenome studies have been successful at resolving deep relationships within the mosses and liverworts, whereas single-gene analyses have advanced understanding of hornwort evolution.