I review the theory and practice behind as reported by Patterson (in: Joysey, Friday (eds) Problems of phylogenetic reconstruction, Academic Press, London, 1982) the criterion of conjunction in plant systematics and evolution, with a focus on: (1) de Pinna (Cladistics 7:367–394, 1991) analysis of homology in the cladistic framework; (2) Hawkins’ (in: Scotland, Pennington (eds) Homology and
... [Show full abstract] systematics: coding characters for phylogenetic analysis, Taylor and Francis, London, 2000) survey of character coding; (3) Sereno (Cladistics 23:565–587, 2007) view of neomorphic and transformational characters; (4) character coding and polymorphic taxa; and (5) the relationship between character coding and plant variation using examples cited by Hawkins (in: Scotland, Pennington (eds) Homology and systematics: coding characters for phylogenetic analysis, Taylor and Francis, London, 2000). I coin the term “Replicable homology,” in contrast to serial homology, to make reference to the presence of multiple copies of the same structure or part in the same organism. I conclude that by Patterson’s (in: Joysey, Friday (eds) Problems of phylogenetic reconstruction, Academic Press, London, 1982) criterion is an important tool in order to identify neomorphic characters and that it cannot be applied to transformational characters. Conventional coding is the appropriate way to code characters, whereas both conjunction and unifying coding should be abolished from character analysis, as they are in disagreement with the view that a single character state must contain a mutually exclusive condition in relation to other character states.
