title: Vascular architecture in shoots of early divergent vascular plants, Lycopodium clavatum and Lycopodium annotinum.
abstract: Lycopodium represents a phylogenetically distinct clade of basal vascular plants with anatomical characters that have no parallel in other lineages. Thus, knowledge of lycopod structure and development may reveal important information about the common ancestors of all vascular plants. Here we report the unique architecture of the conducting system in Lycopodium annotinum and Lycopodium clavatum. Based on multiple series of anatomical sections, we reconstructed spatial relationships between microphylls and the stelar system. Analysis revealed that protoxylem ribs (PXR) were vertical, regardless of type of phyllotaxis, and their numbers were variable. Microphyll traces (MTr) were randomly distributed between ribs, resulting in the absence of defined sympodia and varied lengths of MTr. Dichotomous branching contributed to additional features, for example occurrence of mesarch protoxylem, affecting stele structure and PXR numbers. Our data showed limited interrelationships between lycopod vasculature and microphyll phyllotaxis. This may suggest that both systems developed independently, then evolved together to form the integrated supply system. Thus vasculature in extant lycophytes may be less functionally efficient than in seed plants, where consistent leaf-trace lengths guarantee predictable energy utilization during ontogeny. Differences may result from the phylogenetically different origin of microphylls, and the level of vascular complexity.
authors.affiliation: Institute of Plant Biology, Wrocław University, Kanonia 6/8, 50-328 Wrocław, Poland.
authors.forename: Edyta M
authors.initials: EM
authors.lastname: Gola
authors.affiliation: Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Judith A
authors.initials: JA
authors.lastname: Jernstedt
authors.affiliation: Institute of Plant Biology, Wrocław University, Kanonia 6/8, 50-328 Wrocław, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Zagórska-Marek
mesh_terms: D014644:Genetic Variation; D032502:Lycopodium / Q000033:anatomy & histology* / Q000145:classification* / Q000235:genetics; D018520:Plant Shoots / Q000033:anatomy & histology*; D052584:Xylem / Q000033:anatomy & histology