The lineage is considered to represent the most ancient line within "Allium", and to be the only lineage that is purely bulbous, the other two having both bulbous and rhizomatous taxa. Within the lineage "Amerallium" is a sister group to the other two subgenera ("Microscordum"+"Nectaroscordum"). Nearly all the species in this lineage of five subgenera are accounted for by subgenus "Melanocrommyum", which is most closely associated with subgenera "Vvedenskya" and "Porphyroprason", phylogenetically. These three genera are late-branching whereas the remaining two subgenera, "Caloscordum" and "Anguinum", are early branching. The third evolutionary line contains the greatest number of sections (seven), and also the largest subgenus of the genus "Allium": subgenus "Allium", which includes the type species of the genus, "Allium sativum". This subgenus also contains the majority of the species in its lineage. Within the lineage, the phylogeny is complex. Two small subgenera, "Butomissa" and "Cyathophora" form a sister clade to the remaining five subgenera, with "Butomissa" as the first branching group. Amongst the remaining five subgenera, "Rhizirideum" forms a medium-sized subgenus that is the sister to the other four, larger, subgenera. This line may not be monophyletic. The majority of "Allium" species are native to the Northern Hemisphere, being spread throughout the holarctic region, from dry subtropics to the boreal zone, predominantly in Asia. Of the latter, 138 species occur in China, about a sixth of all "Allium" species, representing five subgenera. A few species are native to Africa and Central and South America. A single known exception, "Allium dregeanum" occurs in the Southern Hemisphere (South Africa). There are two centres of diversity, a major one from the Mediterranean Basin to Central Asia and Pakistan, while a minor one is found in western North America. The genus is especially diverse in the eastern Mediterranean. Species grow in various conditions from dry, well-drained mineral-based soils to moist, organic soils; most grow in sunny locations, but a number also grow in forests (e.g., "A. ursinum"), or even in swamps or water.