Utility of the plastid gene matK in reconstruction of the phylogeny of the pair families Apocynaceae - Asclepiadaceae (Dicotyledones, Gentianales) and critical re-examination of palynological characters used to delimit infra-familial sub-units <B>Utility of the plastid gene matK in reconstruction of the phylogeny of the pair families Apocynaceae - Asclepiadaceae (Dicotyledones, Gentianales) and critical re-examination of palynological characters used to delimit infra-familial sub-units</B><P> </B><EM><B></B></EM><B>(1) Laure Civeyrel and (2) Mark W. Chase <BR> (1) </B>Paleoenvironnements et Palynologie, ISEM - c.c. 61, Universite Montpellier II, 34095 Montpellier, France<B><BR> (2) </B>Molecular Systematics Section, Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK<B></B><P> The family Asclepiadaceae (Dicotyledones, Gentianales) was created by Brown in 1810 by splitting in two the family Apocynaceae of Jussieu established in 1789. A molecular phylogeny is proposed here for 46 species in the order Gentianales, including 15 Apocynaceae and 22 Asclepiadaceae. One of the most variable plastid genes (matK) has been used for this phylogeny and its varibility is assessed and compared to rbcL. In this molecular phylogeny, Asclepiadaceae form a monophyletic group derived from Apocynaceae, which are paraphyletic. Each of the subfamilies of Asclepiadaceae is monophyletic but not the tribes of the subfamily Asclepiadoideae and subfamilies or tribes of Apocynaceae.The morphological characters used to make this distinction were mainly palynological, such as presence of tetrads or pollinia and number and orientation of pollinia. Those characters, used in higher taxonomic delimitation (families, subfamilies and tribes), are here critically reexamined and compared to the molecular phylogeny.<P>