A comparative review of the vascular system in seed plants and humansIn the evolutionary tree of life, all biotic organisms are believed to arise from a common ancestor. Organisms that fall within the eukaryotic kingdom of Plantae are known to have appeared around the same time as those in the eukaryotic kingdom of Animalia: the Paleozoic era, approximately 500 million years ago (MYA) (Raven et al., 2008). Despite their chronological similarity, their evolutionary diversity is especially great in the most advanced organisms: humans and seed plants. A key system that illustrates this diversity is the vascular system (or the cardiovascular system in humans). The vascular system of the respective lines of organisms shows similarities in origin, circulation of food and water, while at the same time showing differences in disease prevention and dependence on the environment. Genetic mapping confirmed that the origin of the plants comes from an ancestral algae. Modern phylogenetics classifies green algae and higher-order plants into a new kingdom called Viridiplantae. As Viridiplantae organisms evolved, they eventually expanded from freshwater and escaped land. Horizontal gene transfer (HGT) and selective pressures have caused widespread diversification and thus given 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, arose 450 MYA, and thus began terrestrial colonization of plants. Tracheophytes appeared for the first time around 420 million years ago, they are plants specialized in vascularization: they were among the first plants to produce tissues that allowed the distribution of material throughout their body... in the center of the 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 vulnerability to xylem cavitation 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 blood flow in the intercostal muscles in athletes during maximal exercise. The Journal of Physiology 587:3665-3677.Zim, S.H. (1968) Blood. New York: William Morrow & Company. Figures 1-3 are courtesy of McGraw-Hill Companies (Raven, 2008). Figure 4 is courtesy of Journal of Obesity (Iacobellis, 2006)