A Morphogenetic Re-evaluation of Haplomitrium Nees (Hepatophyta)

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Language: English

The hepatic genus Haplomitrium has traditionally been of great phylogenetic interest due to its wide array of presumed ancestral characters, some of which are unique and others of which are reminiscent of Takakia and other bryophyte groups. However, the evolutionary affinities, taxonomy, and underlying morphogenetic patterns of Haplomitrium remain uncertain. Of the 13 described species, only 5 have been studied, in part, for developmental patterns, mostly at the light microscope level. New discoveries of both unique and moss-like ultrastructural characters in Takakia, a postulated close relative of Haplomitrium, and recent suggestions that Haplomitrium is more closely related to the Metzgeriales than to the Jungermanniales makes renewed investigations, including ultrastructural analyses of Haplomitrium appropriate.

In this study, the ontogenetic patterns responsible for morphological features of the genus were investigated using experimental culture techniques, light and electron microscopy. Morphogenetic potentials were examined to gain insight into both infrageneric affinities and the phylogenetic relationships with other bryophyte groups, Takakia and the tracheophytes. Of the 13 species studied, 7 are retained and 6 new synonyms are proposed. Likewise, the only other extant member of the Haplomitriales, Steereomitrium, was synonymized with Haplomitrium. The taxa are grouped into two subgenera: subg. Haplomitrium (with two sections: sect. Haplomitrium and sect. Archibryum) and subg. Calobryum. It is concluded that, the genus is a highly plastic, plesiomorphic taxon, probably of Gondwanian origin. Haplomitrium's assemblage of derived traits negate it as the progenitor of either the Metzgeriales or the Jungermanniales. Rather, it appears to have a shared ancestry with the Metzgeriales, and is consequently best classified as a coordinate order in the newly described subclass Metzgeriidae. The shared ancestry of the Haplomitriales and the Metzgeriales suggests that primal hepatics were cylindrical forms with the potential to give rise independently to both dorsiventral and erect, radial gametophytes in response to selective pressures.

Contents

INTRODUCTION 10

MATERIALS AND METHODS 15

Specimens Examined 15

Culture Techniques 15

Light Microscopy Techniques 16

Electron Microscopy Techniques 17

Experimental Techniques 18

MORPHOLOGY AND ONTOGENY 21

The Vegetative Gametophyte 21

Gross Morphology 21

Haplomitrium hookeri (Smith) Nees 24
Haplomitrium ovalifolium Schust. 26
Haplomitrium monoicum Engel 27
Haplomitrium intermedium Berrie 28
Hapiomitrium gibbsiae (Steph.) Schust. 31
Haplomitrium kashyapii Udar & Kumar 33
Haplomitrium mnioides (Lindb.) Schust. 35
Haplomitrium blumii (Nees) Schust. 36
Haplomitrium andinum (Spruce) Schust. 37

Apical Organization 39

Stem Development and Anatomy 51

Leaf Development and Anatomy 63

Oil Bodies 68

Branching 80

The Reproductive Gametophyte 85

Gross Morphology 85

Haplomitrium hookeri (Smith) Nees 86
Haplomitrium ovalifolium Schust. 93
Haplomitrium monoicum Engel 94
Haplomitrium intermedium Berrie 95
Haplomitrium gibbsiae (Steph.) Schust. 96
Haplomitrium indicum (Udar & Chandra) Schust. 99
Haplomitrium dentatum (Kumar & Udar) Engel 100
Haplomitrium grollei Kumar & Udar 102
Haplomitrium kashyspii Udar & Kumar 103
Haplomitrium mnioides (Lindb.) Schust. 106
Haplomitrium blumii (Nees) Schust. 108
Haplomitrium andinum (Spruce) Schust. 109
Haplomitrium giganteum (Steph.) Grolle 111
Steereomitrium minutum E. O. Campb. 112

Antheridial Ontogeny 118

Structure of the Antheridium 124

Archegonial Ontogeny 135

Structure of the Archegonium 140

Sporophyte Protective Structure 142

The Sporophyte 156

Gross Morphology 156

Anatomy and Ontogeny 157

Elaters 166

Haplomitrium hookeri (Smith) Nees 167
Haplomitrium intermedium Berrie 168
Haplomitrium gibbsiae (Steph.) Schust. 168
Haplomitrium indicum Udar & Chandra) Schust. 169
Haplomitrium mnioides (Lindb.) Schust. 169
Haplomitrium blumii (Nees) Schust. 169
Haplomitrium andinum (Spruce) Schust. 169
Steereomitrium minutum E. O. Campb. 170

Spores 170

Haplomitrium hookeri (Smith) Nees 173
Steereomitrium minutum E. O. Campb. 173
Haplomitrium mnioides (Lindb.) Schust. 174
Haplomitrium gibbsiae (Steph.) Schust. 174
Haplomitrium indicum (Udar & Chandra) Schust. 176
Haplomitrium dentatum (Kumar & Udar) Engel 176
Haplomitrium intermedium Berrie 176
Haplomitrium blumii (Nees) Schust. 177
Haplomitrium andinum (Spruce) Schust. 177

Capsule Dehiscence 180
Sporeling Development 183

Ontogenetic Pattern 183

Pattern Comparisons and Phylogenetic
Implications 189

Experimental and Culture Studies 194

Spore Culture Experiments 194

Culture-Induced Adult Phenovariations 204

TAXONOMIC TREATMENT 210

Metzgeriidae Bartholomew-Began 212

Haplomitriales Buch ex Schljakov 213
Haplomitriaceae Dědeček 214
Haplomitrium Nees 216

Structural Features Useful for Subgeneric and Interspecific Differentiation 220

Subdivision of the Genus and Relationships Among Taxa 222

Keys to the Taxa of Haplomitrium 224

Key to the Subgenera and Sections of Haplomitrium 224

Key to the Species of the Subgenus Haplomitrium section Haplomitrium 224

Key to the Species of the Subgenus Haplomitrium section Archibryum 225

Key to the Species of the Subgenus Calobryum 226

Vegetative Key to the Species of Haplomitrium 226

Subgenus Haplomitrium 227

Subg. Haplomitrium sect. Haplomitrium 227
H. hookeri (Smith) Nees 228
H. hookeri var. hookeri 229
H. hookeri (Smith) Nees var. minutum (E. O. Campb.) Bartholomew-Began 230
H. ovalifolium Schust. 234
H. monoicum Engel 236

Subg. Haplomitrium sect. Archibryum (Schuss.) Engel emend. Bartholomew-Began 238
H. intermedium Berrie 238
H. gibbsiae (Steph.) Schust. 240

Subg. Calobryum (Nees) Schust. 247
H. mnioides (Lindb.) Schust. 247
H. blumii (Nees) Schust. 250

SPECIATION AND PHYLOGENETIC AFFINITIES 256

REFERENCES 270

FIGURES 298

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