A native plant cell (PO:0025606) that is part of a portion of phloem tissue (PO:0005417), has sieve areas in its walls, and lacks a nucleus in its mature protoplast. [source: ISBN:0471245208, POC:Laurel_Cooper]
Comment
Sieve elements function mainly in longitudinal conduction of organic solutes. Classified into sieve cells (PO:0025415) and sieve tube elements (PO:0000289) based on the presence of sieve plates and specialization of sieve areas in different parts of the cell. Develops from either a cambial initial (PO:0000295), a phloem mother cell (PO:0000400), or a cell of the procambium (PO:0025275).