A portion of meristem tissue (PO:0009013) that is the outermost layer of a shoot apical meristem (PO:0020148) and gives rise to a shoot system epidermis (PO:0006035). [source: GR:Pankaj_Jaiswal, PMID:11283725, PMID:12221985, POC:Laurel_Cooper]
Comment
The cells of the meristem L1 layer divide in a strictly anticlinical fashion.