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In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and synapomorphy all mean a trait shared between species because they share an ancestral species.
Symplesiomorphy – an ancestral trait shared by two or more taxa. Plesiomorphy – a symplesiomorphy discussed in reference to a more derived state. Pseudoplesiomorphy – a trait that cannot be identified as either a plesiomorphy or an apomorphy that is a reversal.
Shared ancestral character states, symplesiomorphies, represent either synapomorphies of a more inclusive group, or complementary states (often absences) that unite no natural group of organisms. For example, the presence of wings is a synapomorphy for pterygote insects, but a symplesiomorphy for holometabolous insects.
Symplesiomorphy – an ancestral trait shared by two or more taxa. Plesiomorphy – a symplesiomorphy discussed in reference to a more derived state. Pseudoplesiomorphy – is a trait that cannot be identified as neither a plesiomorphy nor an apomorphy that is a reversal.
A simple cladogram showing the evolutionary relationships between four species: A, B, C, and D. Here, Species A is the outgroup, and Species B, C, and D form the ingroup. In cladistics or phylogenetics, an outgroup [1] is a more distantly related group of organisms that serves as a reference group when determining the evolutionary relationships of the ingroup, the set of organisms under study ...
In phylogenetics, parsimony is mostly interpreted as favoring the trees that minimize the amount of evolutionary change required (see for example [2]).Alternatively, phylogenetic parsimony can be characterized as favoring the trees that maximize explanatory power by minimizing the number of observed similarities that cannot be explained by inheritance and common descent.
Hennig coined the key terms synapomorphy, symplesiomorphy, and paraphyly. He also asserted, in his "auxiliary principle", that "the presence of apomorphous characters in different species 'is always reason for suspecting kinship [i.e., that species belong to a monophyletic group], and that their origin by convergence should not be presumed a ...
Any smooth function on a symplectic manifold gives rise, by definition, to a Hamiltonian vector field and the set of all such vector fields form a subalgebra of the Lie algebra of symplectic vector fields. The integration of the flow of a symplectic vector field is a symplectomorphism.