Systematics and Evolution of the Genera of the Marchantiales

About this book

Language: English

This survey of the order Marchantiales contains descriptions of the order and of the genera including morphological, ontogenetic and cytological characters, reassessed with living plant material, ecological data, life history traits, geographical distributions and keys, as well as an outline of published evolutionary classifications and scenarios based on morphological, phytochemical and molecular sequence data. The relationships of the order with the other liverwort orders, with the mosses and with the land plants are summarized.

The phylogenetic tree of the order is constructed with a cladistic parsimony analysis, based on 43 selected characters, with outgroup genera from the orders Sphaerocarpales, Monocleales and Metzgeriales. It results in a consensus tree in which the two main sister groups are the Ricciineae on one hand and the Corsiineae-Targioniineae-Marchantiineae on the other.

Character analysis and screening of character evolution in character state graphs derived from the consensus tree show that the ancestors of the Marchantiales had relatively simple morphological traits. Progressively more complex sex-related gametophytic structures and sporophytes with larger foot, seta and capsules are seen in one of the sister groups, which includes the suborders Corsiniineae, Targioniineae and Marchantiineae, with the evolution of stalked gametangiophores, not found in any other order of liverworts. Reductions in these same characters are observed in the other sister group, the Ricciineae.

Sex-related and sporophytic characters show higher stability, with fewer homplasies than the characters of the gametophyte. Seasonality of the former, and differences in the action of environmental conditions upon the haploid, exposed gametophyte as compared with the diploid, sheltered sporophyte, may be invoked as an explanation.

Little support for the proposed phylogenetic reconstruction can be obtained from geographical distribution because many genera have worldwide ranges. No hypothesis on the place or time of origin of the order can be put forward. However, the most ancient stock of taxa seems to have inhabited temperate to hot-temperate, continental areas.

The size of genera, species structure and differences in levels of genetic variability among species, are not reflected by tree topology. Instead, life history patterns appear to be linked to phylogeny. An independent statistical correspondence analysis, including 12 life history characteristics of 230 marchantialean species, discloses four groups of taxa with similar life history patterns. These groups show habitat specificity and are strongly determined by generic and familial membership. Life history traits appear to be shared as a result of common ancestry rather than of convergence due to habitat conditions. Diversification in life history patterns seem to have occurred at either the generic or the familial level, and seem to have been conserved in the course of evolution.

The traditional assemblage of genera into families and of families into suborders is confirmed, except for the Targioniaceae and Peltolepis. Some taxa of subfamilial rank are paraphyletic. On the other hand, tree topology fails to confirm the basic hypotheses of both the antithetic and homologous theories, on which formerly published classifications and evolutionary scenarios, as well as the classification in the current use, were built. These theories postulated respectively progressive or reductive evolution of the sporophytic generation. The sporophytes remain small in all taxa of the Marchantiales.

The phylogenetic reconstruction does not confirm most of the assumptions on evolution based on phytochemical data, or on molecular sequence data, sampled at present for only a small number of species. In the future, alanysis of other, especially ontogenetic, data and more complete sets of phytochemical and molecular sequence data will be necessary to test the robustness of the proposed phylogenetic hypothesis. A critical reevaluation of morphological characters might then be within reach.

Contents

Abstract 7
Introduction 9
      Material and methods 10
      Acknowledgments 11
The order Marchantiales 13
      Description 13
      Delimitation of the order and differences from the other orders 14
      Formerly proposed evolutionary scenarios 16
            Evolutionary scenarios based on morphological and ontogenetic data 16
            Evolutionary scenarios derived from phytochemical data 19
            Evolution inferred from molecular data 20
      Relationships of the Marchantiales with other land plants 20
      Ecology and life history traits 23
      Geographical ranges 23
      Fossil records 25
Keys to genera 27
      Key to genera (fertile plants) 27
      Artificial key to genera (sterile plants) 33
Description of genera 37
      Suborder Monocarpineae 37
      Suborder Ricciineae 38
      Suborder Corsiniineae 42
      Suborder Targioniineae 45
      Suborder Marchantiineae 48
Outgroup taxa 73
      Sphaerocarpales 73
      Monocleales 75
      Metzgeriales 76
The phylogenetic reconstruction 79
      Selection of characters 79
            Excluded characters 79
      Selection of outgroup taxa 83
      Cladistic analysis 84
            Character treatment 84
            The data set 85
            Parsimony analysis 85
      Tree topology 87
      Apomorphies and homoplasies 92
      Character correlations and convergences 92
Evaluation of published hypotheses on evolution 93
      Evaluation of evolutionary scenarios and of current classification 94
      Evaluation of taxa of suborder, family and subfamily rank 95
      Relationships of genera 95
Character evolution 97
            Thallus 97
            Asexual reproduction 103
            Chromosome numbers 103
            Sexual structures 103
            Antheridia and antheridiophores 107
            Archegonia 109 This Sl
            Archegoniophores 113
            Sporophyte 115
            Spore germination 119
      Inferences on character states of marchantiaiean ancestors 120
      Gains and losses 120
Analysis of life history patterns 123
      The data set 123
      The treatments 125
      Correlations between life history traits 132
      Synopsis of the groups and their morphological correlates 133
      Life history patterns and phylogeny 135
Conclusions 141
References 142
Index 151

Customer Reviews