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The term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος (mónos), meaning "alone, only, unique", and φῦλον (phûlon), meaning "genus, species", [4] [5] and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a unique common ancestor.
This definition assigns species on the basis of amount of divergence associated with reproductive incompatibility, which is measured essentially by number of autapomorphies. [6] This grouping method is often referred to as the " monophyletic species concept" or the "phylospecies" concept and was popularized by D.E. Rosen in 1979.
Evolutionary grade – Non-monophyletic grouping of organisms united by morphological or physiological characteristics; Lineage (evolution) – Sequence of populations, organisms, cells, or genes that form a line of descent; Molecular phylogenetics – Branch of phylogeny that analyzes genetic, hereditary molecular differences
In biological phylogenetics, a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group, [1] is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. [2]
It was based on the assumption that higher-ranked taxa could represent specific morphological innovations. Although this approach was criticized as it relied on artificial and non-monophyletic taxa, it provided valuable insights into the evolution of disparity. Some conclusions have been confirmed by subsequent quantitative metrics.
The term paraphyly, or paraphyletic, derives from the two Ancient Greek words παρά (pará), meaning "beside, near", and φῦλον (phûlon), meaning "genus, species", [2] [3] and refers to the situation in which one or several monophyletic subgroups of organisms (e.g., genera, species) are left apart from all other descendants of a unique common ancestor.
Phylogenies showing the terminology used to describe different patterns of ancestral and derived trait states. [1] Imaginary cladogram. [2] The yellow mask is a plesiomorphy for each living masked species, because it is ancestral. [2]
However, this classification system is in disuse due to the kingdom's non-monophyletic nature. [25] While Ochrophyta is the preferred name by general protistologists and protozoologists, the name Heterokontophyta is considered more familiar among phycologists. [7]