A comparative examination of the vascular system of seed plants and humans In the evolutionary tree of life, all biotic organisms are thought to derive from an ancestor common. It is known that organisms belonging to the eukaryotic kingdom Plantae appeared at the same time as those of the eukaryotic kingdom Animalia, namely the Paleozoic era, approximately 500 million years ago (MYA) (Raven et al., 2008). Despite their chronological resemblance, their evolutionary diversity is particularly great in their most advanced organisms: humans and seed plants. A key system that illustrates this diversity is the vascular system (or cardiovascular system in humans). The vascular system of the respective lineages of organisms shows similarities in origin, movement of food and water, while showing differences in disease prevention and environmental dependence. Genetic mapping has confirmed that the origin of the plants comes from ancestral algae. Modern phylogenetics classifies green algae and higher order plants into a new kingdom called Viridiplantae. As Viridiplantae organisms evolved, they eventually expanded out of fresh water and escaped onto land. Horizontal gene transfer (HGT) and selective pressures caused great diversification and thus gave rise to three types of land plants (Figure 1): bryophytes, tracheophytes and seed plants (*Puigbò et al., 2009; Raven et al., 2008). ). Bryophytes, which include liverworts, hornworts, and mosses, appeared 450 MYA and thus began the terrestrial colonization of plants. Tracheophytes first appeared around 420 MYA. These are plants specialized in vascularization. They were among the first plants to produce tissues that allowed the distribution of matter throughout their bodies...... middle of paper ...... Life' in the thicket of the phylogenetic forest. BMC Journal of Biology 8:59. Raven, PH, Johnson, GB, Losos, JB, Mason, KA, Singer, SR (2008) Biology. Singapore: McGraw-Hill International.*Stiller, V (2009) Soil salinity and drought alter wood density and xylem cavitation vulnerability of bald cypress (Taxodium distichum) seedlings. Environmental and Experimental Botany 67: 164-171. Vaucher, H (2003) Tree bark. Portland: Timber Press.*Vogiatzis, I, Athanasopoulos, D, Habazettl, H, Kuebler, WM, Wagner, H, Roussos, C, Wagner, PD, Zakynthinos, S (2009) Limitation of intercostal muscle blood flow in athletes during maximal exercise. The Journal of Physiology 587: 3665-3677. Zim, SH. (1968) Blood. New York: William Morrow & Company. Figures 1-3 are courtesy of McGraw-Hill Companies (Raven, 2008). Figure 4 is courtesy of the Journal of Obesity (Iacobellis, 2006)