A vascular leaf initiation stage (PO:0007040) during which the vascular leaf founder cells (PO:0025592) of the shoot apical meristem (PO:0020148) form a vascular leaf anlagen (PO:0025431). [source: POC:Brian_Atkinson, POC:Laurel_Cooper, TAIR:Katica_Ilic]
Comment
The initial stage of leaf development when cells in the shoot apical meristem (PO:0020148) are already determined to form a vascular leaf primordium (PO:0000017), but the primordium is not yet morphologically distinguishable.