In Linnaeus' time, a two-kingdom system of classification with Plantae and Animalia kingdoms was developed that included all plants and animals, respectively. This system did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) organisms. Bacteria, blue-green algae, fungi, ferns, gymnosperms and angiosperms all possess a cell wall. Animals lack a cell wall.