The correct answer is their ability to bear seeds.Concept:Plant kingdom:It includes eukaryotic, multicellular, autotrophic organisms, that have a cell wall made up of cellulose.It is further subdivided into five divisions- Thallophyta, Bryophyta, Pteridophyta, gymnosperms, and Angiosperms.Explanation:Classification of the plant kingdom:The first level of classification is whether the plant body is differentiated into true roots, leaves, and stems.Followed by the presence of vascular tissue and then the ability to bear seeds. Plants are broadly divided into two main categories- Cyptogems (non-phanerogams) and phanerogams. Phanerogams are distinguished from non-Phanerogams by their ability to bear seeds.