(1) The quartan malarial parasite Plasmodium malariae in its segmented or mature phase. (2) A grouping of cells characteristic of neoplasms of neuroblastic, neuroectodermal, or ependymal origin; nuclei form a ring from which neurofibrils, which can be demonstrated by silver impregnation, extend to interlace in the center (Homer-Wright rosette); arrangement of ependymal cells around a vessel (perivascular pseudorosette) or around a space or channel (transependymal rosette). (3) Roselike coiling of the uterus among certain pseudophyllidean tapeworms, such as Diphyllobothrium latum. (4) Cells of one type surrounding a cell of another type. [Fr. a little rose]