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In phylogenetics, basal is the direction of the ''base'' (or root) of a rooted phylogenetic tree or cladogram. Clade ''C'' may be described as basal within a larger clade ''D'' if its root is directly linked (adjacent) to the root of ''D''. If ''C'' is the only clade of a given taxonomic rank that is basal within ''D'', ''C'' may be described as ''the'' basal taxon of that rank within ''D''. While there must always be two or more equally basal clades sprouting from the root of every cladogram, those clades may differ widely in rank and/or species diversity. Greater diversification may be associated with more evolutionary innovation, but ancestral characters should not be imputed to the members of a less species-rich basal clade without additional evidence, as there can be no assurance such an assumption is valid. In general, clade ''A'' is more basal than clade ''B'' if ''B'' is a subgroup of the sister group of ''A''. Within large groups, "basal" may be used more loosely to mean 'closer to the root than the great majority of', and in this context terminology such as "very basal" may arise. ==Examples== A basal group forms a sister group to the rest of the larger clade, such as in the following example: }} The term ''basal'' can be correctly applied to clades of organisms, but not to lineages or to individual traits possessed by the organisms—although it may be misused in these ways in technical literature. While "basal" applies to clades, ''characters'' or traits are usually considered derived if they are absent in a basal group, but present in other groups. This assumption only holds true if the basal group is a good analogy for the last common ancestor of the group. "Ancestral" or "basal" are preferred to "primitive", which may carry false connotations of inferiority or a lack of complexity. The flowering plant family Amborellaceae, restricted to New Caledonia in the southwestern Pacific, is a basal clade of extant angiosperms, containing the most basal species, genus, family and order within the group (out of a total of about 250,000 angiosperm species). While the traits of ''Amborella trichopoda'' are regarded as providing significant insight into the evolution of flowering plants, they are a mix of archaic and derived features that have only been sorted out via comparison with other angiosperms and their positions within the phylogenetic tree (the fossil record could potentially also be helpful in this respect, but is absent in this case). }} Within the primate family Hominidae, gorillas (eastern and western) are a sister group to common chimpanzees, bonobos and humans. These five species form a clade, the subfamily Homininae, of which ''Gorilla'' is the basal genus. |}}}} However, orangutans are a sister group to Homininae and are the basal genus in the family as a whole. }}}}}} Subfamilies Homininae and Ponginae are both basal within Hominidae, but given that there are no nonbasal subfamilies in the cladogram it is unlikely the term would be applied to either. In general, a statement to the effect that one group (e.g., orangutans) is basal, or branches off first, within another group (e.g., Hominidae) may not make sense unless the appropriate taxonomic level(s) (genus, in this case) is specified. If that level cannot be specified (i.e., if the clade in question is unranked) a more detailed description of the relevant sister groups may be needed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Basal (phylogenetics)」の詳細全文を読む スポンサード リンク
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