Abstract: This paper summarizes the history of classifications of Paleozoic seeds and  revaluates the previous classification systems of Paleozoic detached seeds. The current status  of studies on Paleozoic. gymnosperms: has been deteched seeds and whole fossil  gymnosperms indicates that Seward’s  classification system for Paleozoic seeds inadequate  since all the seeds of Cardiocarpales in his system are not cordaitean female reproductive or-  gans as Seward’s  suggested. It is shown from investigations of whole fossil plants that the  members of Cardiocarpales were derived from at least three different major groups of  Paleozoic gymnosperms. Moreover, Meyen’s  suggestion that the gymnosperms be classified  based on symmetry of seeds has been little supported since all the fossil gymnosperms have  not shown structurally preserved seeds and organic attachment. In order to relate detached seeds to whole fossil gymnosperms, the present author sug-  gests that five families: Lagenostomaceae, Pachytestaceae, Callospermariaceae, Cryptospe-  rmaceae  and  Cardiocarpaceae  be established  for  Paleozoic  seeds  and  the Order  Trigonocarpales be renamed as Pachytestales since the genus Trigonocarpus does not now in-   clude structurally preserved seeds. Thus, the five families may be considered either as  subdivisions of the three orders of detached seeds: Lagenostomales, Pachytestales and  Cardiocarpales, or as female reproductive organs of whole fossil gymnosperms of the five  Permo-Carboniferous major groups:  Lyginopteridales, Medullosales, Callistophytales  Gigantopteridales and Cordaitales. A Key to Paleozoic seeds is provided as follows: A.  Seeds with a cupule; integument thin, simple, deeply lobed and less differe- ntiated;nucellus united to integument up to the base of pollen chamber; pollen chamber complex  .................................  Lagenostomales, Lagenostomaceae A.  Seeds without a cupule; integument thick, complex, unlobed and differentiated into several layers; nucellus free within integument except at the base; pollon chamber simple  ................................................................................................  B   B.  Seeds radially symmetrical in shape; integumentary bundles present; nucellus bun- dles typical  ...................................................  Pachytestales, Pachytestaceae   B.  Seeds bilaterally symmetrical in shape; integumentary bundles present or absent; nucellus bundles often untypical  ....................................  C (Cardiocarpales)   C.  Bundles absent in integument; main bundle C-shaped in transverse section with a sclerenchyma bundle  ............................................  Cryptospermaceae   C.  Bundles present in integument; main bundle not C-shaped in transverse section without a sclerenchyma bundle  .........................................................  D D.  Seeds very small with secretory cavities in integument; nucellus bundles limit-   ed in nucellus platform  ..........................................  Callospermariaceae D.  Seeds large without secretory cavities in integument; nucellus bundles limited   in nucellus platform or not  ...................