Question: Is it feasible to establish a classification of large biotic units of the world related to climatic types? Study area: The world. Methods: A total of 616 localities have been selected, their climatic parameters calculated and subjected to a PCA. The climatic characterization of biomes and subbiomes has been completed after data analysis. Results: A hierarchical classification is proposed for the biotic units within four main domains: Cryocratic, Mesocratic, Xerocratic and Thermocratic, divided into 7 ecozones, 9 biomes and 20 subbiomes linked to climatically defined territories. Most of the units are intercontinental. The mountains represent an abbreviated version of the latitudinal zonation and the altitudinal belts are related to the corresponding units of the lowlands. For the bioclimatic units, a parallel classification is proposed to fit with that of the biotic units: 4 Macrobioclimates and 10 bioclimates. Furthermore, 7 ombrotypes and 7 thermotypes are recognized to frame the climatic variation within each climatic territory due to terrain ruggedness, particularly in relation to large or medium sized mountains. Conclusions: The southern hemisphere is substantially more oceanic than the northern hemisphere. This is due to the distribution of the land masses and the modifying effect they have on the flow of air and marine currents. As a result, there is one biome and one subbiome exclusively found in the northern hemisphere (6. Biome of the steppe, and 5.b Continental scrub and woodlands subbiome) and two others which are almost confined to it (2. Biome of the boreal forest, and 3. Biome of the temperate deciduous forests). The 7. Biome of the deserts and 5. Biome of the temperate aridiestival evergreen forests and shrublands occur on the western side of the continents and expand in their interior favoured by rain shadow and continentality effects.<br> Taxonomic reference: The Plant List (2013).<br> Abbreviations: ITCZ = Inter Tropical Convergence Zone; NH = Northern Hemisphere; PCA = Principal Component Analysis; SH = Southern Hemisphere.
