Cysteine proteinases of unique Asn/Asp specificity (legumains) were first detected and studied as  enzymes catalyzing proteolytic processing of seed storage globulins and their further degradation  during seed germination. For the moment, it is known that legumains are characteristic both of  plants and of a wide range of animals, several ancient eukaryotes as well as of bacteria and  archaea. Because of their narrow specificity, legumains catalyze a wide range of processes related  to plant and animal vital functions. Eukaryote legumains are synthesized as inactive precursors  containing conserved N- and C-terminal domains and  a  rather  variable  activation  peptide  in   between.  Activation  of  plant  seed  and mammalian legumains occurs due to autocatalytic cleavage  inside the activation peptide followed by detachment of the C-terminal domain that blocks the  active site amino acids positioned inside the N-terminal domain. In contrast to eukaryote  legumains, prokaryote legumains  lack  the  C-terminal  domain.  For  the  moment,  a  wide  range   of  amino  acid sequences of plant and animal legumains as well as legumains from ancient  eukaryotes and prokaryotes became available. Therefore, a detail analysis of successive  evolutionary stages of plant legumains was conducted in this investigation. When amino sequences of  legumains from Arabidopsis thaliana and Homo sapience were used as queries, a wide collection of  seed legumains and their precursors from spore plants, animal legumains as well  as  legumains   from  ancient  eukaryotes  and  prokaryotes  was  collected.  To  follow evolutionary pathway of  plant and animal legumains full-length amino acid sequence of legumains  from  Trichomonas  species   estimated  as  most  ancient  organism  among eukaryotes  were  used  as  roots.  Three  basic   clusters  were  detected  in  respective evolutionary tree: the ancient group of Alveolata and  Stramenopiles legumains, Plant and Metazoa legumains. The same clusters were observed when the  sequence region analyzed was restricted to the N-terminal domains and prokaryote legumains were  used as roots. Legumain sequences  within plant cluster strongly follow the evolutionary pathway of  species: green algae, mosses, seed plants. Exon/intron structures of legumain genes from land  plants are almost identical and close to that of Klebsormidium nitens legumain (green alga,   Charophyta).  In  contrast,  position  of  introns  in  Chlorophyta  legumain  genes  is completely  different. Additionally, long variable inserts inside the C-terminal domain are specifically   characteristic  of  amino  acid  sequences  only  from  Chlorophyta  legumain species.  These   observations  both  are  in  line  with  the  plant  tree  of  life,  estimated Chlorophyta as most ancient green algae.