The common characteristic feature of plant sieve tube and mammalian erythrocyte is the absence of nucleus. Sieve tubes are the component of phloem and, do not contain nucleus. Similarly, erythrocytes in mammalian cell also do not possess nucleus. Erythrocytes are the RBCs which helps in gaseous exchange.
Mitochondria is absent in sieve tube cells. Pigment haemoglobin is present in mammalian erythrocytes but not in sieve tube cells. Cell wall is made of cellulose and is present in all plant cells, and thus absent in erythrocytes.