RNA editing affects messenger RNAs and transfer RNAs in plant mitochondria by site-specific exchange of cytidine and uridine bases in both seed and nonseed plants. Distribution of the phenomenon among bryophytes has been unclear since RNA editing has been detected in some but not all liverworts and mosses. A more detailed understanding of RNA editing in plants required extended data sets for taxa and sequences investigated. Toward this aim an internal region of the mitochondrial nad5 gene (1104 nt) was analyzed in a large collection of bryophytes and green algae (Charles). The genomic nad5 sequences predict editing in 30 mosses, 2 hornworts, and 7 simple thalloid and leafy liverworts (Jungermanniidae). No editing is, however, required in seven species of the complex thalloid liverworts (Marchantiidae) and the algae. RNA editing among the Jungermanniidae, on the other hand, reaches frequencies of up to 6% of codons being modified. Predictability of RNA editing from the genomic sequences was confirmed by cDNA analysis in the mosses Schistostega pennata and Rhodobryum roseum, the hornworts Anthoceros husnotii and A. punctatus, and the liverworts Metzgeria conjugata and Moerckia flotoviana. All C-to-U nucleotide exchanges predicted to reestablish conserved codons were confirmed. Editing in the hornworts includes the removal of genomic stop codons by frequent reverse U-to-C edits. Expectedly, no RNA editing events were identified by cDNA analysis in the marchantiid liverworts Ricciocarpos natans, Corsinia coriandra, and Lunularia cruciata. The findings are discussed in relation to models on the phylogeny of land plants.

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Complete nuclear-encoded small-subunit 18S rRNA (= SSU rRNA) gene sequences were determined for the prasinophyte green alga Mantoniella squamata; the charophycean green algae Chara foetida, Coleochaete scutata, Klebsormidium flaccidum, and Mougeotia scalaris; the bryophytes Marchantia polymorpha, Fossombronia pusilla, and Funaria hygrometrica; and the lycopod Selaginella galleottii to get a better insight into the sequential evolution from green algae to land plants. The sequences were aligned with several previously published SSU rRNA sequences from chlorophytic and charophytic algae as well as from land plants to infer the evolutionary relationships for major evolutionary lineages within the Chlorobionta by distance matrix, maximum parsimony, and maximum likelihood analyses. Phylogenetic trees created by the different methods consistently placed the Charophyceae on the branch leading to the land plants. The Charophyceae were shown to be polyphyletic with the Charales ("charalean" algae) diverging earlier than the Coleochaetales, Klebsormidiales, Chlorokybales, and Zygnematales ("charophycean" algae) which branch from a point closer to the land plants in most analyses. Maximum parsimony and maximum likelihood analyses imply a successive evolution from "charophycean" algae, particularly Coleochaetales, to bryophytes, lycopods, and seed plants. In contrast, distance matrix methods group the bryophytes together with the "charophycean" algae, suggesting a separate evolution of these organisms compared with the club moss and the seed plants.

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The use of molecular biological markers in taxonomy has created a new dimension for the classification of all groups of organisms. The determination of base exchanges in defined genes within a group of organisms provides a range of quantitative parameters in addition to morphological, anatomical or developmental characters. Even though an exact knowledge of morphological data, and a familiarity with many details, gives a taxonomist a good feeling ("Fingerspitzengefiihl") of the relations between taxa, molecular parameters remain useful. Where there is controversy concerning the evolution or the taxonomy of a group, the study of molecular data based on suitable genes remains more than useful for clarifying the phylogeny.For this kind of molecular analysis the most productive genes are those which contain an alternation of conserved and variable regions, which in principle makes them appropiate for analyses on different evolutionary time scales. In green plants, the chloroplast-encoded gene of the large subunit of rubisco (rbcL), and the nuclear-encoded 18 S rRNA gene are the most commonly used, and they have also been chosen for bryophyte taxonomy.After the fundamental developmental research work of Wilhelm Hofmeister (1851) the systematics of bryophytes, especially their position within the plant kingdom, seemed to be unequivocally clear. julius Sachs (1875) wrote that Hofmeister's work had opened our eyes to the evolution of mosses, ferns and flowering plants, and that the descendence theory of Darwin had only to explain what developmental history had shown.Discussion nevertheless continued, because the classification of bryophytes into the three main groups, hornworts, liverworts and mosses, did not satisfy all aspects of taxonomic relations (Schuster, 1984b) deduced from ontogeny, developmental physiology, and morphology (Schuster, 1984a;Crandall-Stotler, 1981. The significance of thallic growth versus leafy shoot growth seems to be the subject of the most confusing discussion. In the past few years research has, therefore, concentrated on the clarification of the taxonomy of bryophytes by partial (Waters et al., 1992; Mishler et aI., 1992; Mishler et al., 1994) or complete 18 S rRNA sequence analysis (Kranz et aI.