Véronique Daviero-Gomez

Nothia aphylla: The Issue of Clonal Development in Early Land Plants

The Early Devonian herbaceous plant Nothia aphylla from the Rhynie Chert (Aberdeenshire, Scotland) is a striking and informative example of a developmental strategy in early land plants. Although simple and primitive in anatomy, N. aphylla combined sexual and vegetative reproduction in order to survive and colonize moist patches near ponds and hot springs in an alluvial plain. Large colonies formed, being mainly composed of clonal individuals derived from asexual reproduction, i.e., the separation of similar units created by lateral branching. Each unit consisted of a single rhizome bearing one ventral, rhizoidal ridge and one distal, aerial, photosynthetic, and fertile branched shoot. The rhizomes allowed for an indeterminate horizontal propagation, while the erect photosynthetic shoots furnished a limited vertical occupation. Similar architecture and clonal development existed among coeval plants, such as Aglaophyton major and Horneophyton lignieri, and persisted through geologic time. Nowadays asexual reproduction is still a successful strategy in bryophytes, pteridophytes, and angiosperms.

Pseudoasterophyllites cretaceus from the Cenomanian (Cretaceous) of the Czech Republic: A possible link between Chloranthaceae and Ceratophyllum

Pseudoasterophyllites cretaceus from the Cenomanian of Bohemia was recently recognized as an angiosperm by association with stamens containing monosulcate pollen of the Tucanopollis type. New material indicates that the stamens were borne in short spikes, with each stamen subtended by a bract, whereas the carpels were solitary and contained a single pendent, orthotropous ovule. We have investigated the phylogenetic position of Pseudoasterophyllites by including it in a morphological analysis of extant angiosperms using backbone constraint trees that represent the current range of hypotheses on relationships of the five mesangiosperm clades. With a backbone tree in which Chloranthaceae are linked with magnoliids and Ceratophyllum with eudicots, the most parsimonious position of Pseudoasterophyllites is sister to Chloranthaceae, but a sister-group relationship to Ceratophyllum is only one step less parsimonious. With a backbone tree in which Chloranthaceae and Ceratophyllum form a clade, Pseudoasterophyllites is sister to Ceratophyllum, based on derived features shared with both Chloranthaceae and Ceratophyllum plus solitary female flowers (as in Ceratophyllum). Similar results are obtained when Pseudoasterophyllites is added to the analysis with other fossils inferred to be related to Chloranthaceae and/or Ceratophyllum. If the plants that produced Tucanopollis pollen in the Barremian-Aptian of Africa–South America are related to Pseudoasterophyllites, these results suggest that Chloranthaceae and Ceratophyllum are relicts of one of the most important early radiations of angiosperms, which included not only colonizers of disturbed terrestrial habitats but also halophytes and aquatics.

Deciphering Early Angiosperm Landscape Ecology Using a Clustering Method on Cretaceous Plant Assemblages

Fossils open up windows on past lives and evolutionary mechanisms inaccessible to other fields of biology. Palaeontology has highlighted five moments of major extinctions in the life history on Earth: Ordovician/Silurian, Late Devonian, Permian/Triassic, Triassic/Jurassic and Cretaceous/Tertiary (Sepkoski, 1986). These five crises shaped life (apparitions versus extinctions of species), as well as diversity, ecology, and landscape. So fossils are not objects only useful for taxonomy and systematics, but their ecological traits can be deciphered to reveal macro-evolutionary processes and landscape ecology.