In the marine crop Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi, it is known that conchospores from heterozygous conchocelis develop into sectored gametophytic blades (chimeras), but archeospores asexually released from haploid blades do not usually grow into chimeric blades. In this study, chimeras with mosaic pattern consisting of the green and wildtype colors were developed from archeospores that were released from a blade piece containing a cell cluster of green color induced by heavy-ion beam irradiation. To make clear whether these archeospores were produced from the green-colored cells or the wildtype-colored cells, cell clusters of the green mutant, wildtype, and mosaic pattern were cut out from the grown chimera, and archeospores were released from each of the three blade pieces. Archeospores from the green-mutant blade piece and from the wildtype blade piece developed into only green-mutant blades and wildtype blades, respectively. In contrast, archeospores from the blade piece with mosaic pattern developed into green-mutant blades, wildtype blades, and chimeric blades with mosaic pattern of the two colors, although the frequency of the chimeras was low. Because each gametophytic cell possesses a single plastid, it is difficult to explain the occurrence of the new chimeras as a mutation of the plastid DNA. Thus, the new chimeras are considered to be due to transposable elements in Pyropia.