root lateral root A root (PO:0009005) that develops from a lateral root primordium (PO:0000016) that is part of another root on the same plant. A lateral root primordium may develops on any root, including a primary root (PO:0020127), on an existing lateral root (PO:0020121), or a shoot-borne root (PO:0000042). In seed plants, a lateral root primordium generally develops from pericycle cells (PO:0025261), but cells of an endodermis (PO:0000252) may also participate in its formation in some species. In ferns, lateral root primordia develop from the endodermis.