APG II system in the context of "Posidoniaceae"

Dioscoreaceae (/ˌdaɪəˌskɔːriˈeɪsii/) is a family of monocotyledonous flowering plants, with about 715 known species in nine genera. The best-known member of the family is the yam (some species of Dioscorea).

The APG system (1998) and APG II system (2003) both place it in the order Dioscoreales, in the clade monocots. However, the circumscription changed in the APG II system, with the 2003 system expanded to include the plants that in the 1998 system were treated in the families Taccaceae and Trichopodaceae.

Zosteraceae (one of the four seagrasses families, Kubitzki ed. 1998) is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an aquatic environment and ribbon-like leaves that lack stomata. Seagrasses are herbaceous and have prominent creeping rhizomes. A distinctive characteristic of the family is the presence of characteristic retinacules, which are present in all species except members of Zostera subgenus Zostera.

Zosteraceae has long been accepted by taxonomists as monophyletic. The APG II system of 2003 recognizes this family and places it in the monocot order Alismatales. The family contains approximately twenty-two species divided between two genera, Phyllospadix and Zostera totalling 22 known species (Christenhusz & Byng 2016 ). Zostera contains three subgenera: Heterozostera (formerly considered a separate genus ), Zostera and Zosterella. Zosteraceae is closely related to Potamogetonaceae, a family of freshwater aquatics.

The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular-based, system of plant taxonomy. Published in 1998 by the Angiosperm Phylogeny Group, it was replaced by the improved APG II in 2003, APG III system in 2009 and APG IV system in 2016.

The Dilleniales are an order of flowering plants, potentially containing one family, Dilleniaceae. The APG III system of 2009, like the earlier APG II system of 2003, left the Dilleniaceae unplaced as to order, while noting that the name Dilleniales was available. Stevens at the Angiosperm Phylogeny Website has subsequently placed Dilleniaceae in the order Dilleniales.

The Cronquist system, of 1981, recognized such an order and placed it in subclass Dilleniidae. It used the following circumscription: