A leaf lamina vein (PO:0020138) that connects directly to a petiole vascular system (PO:0000052) or a shoot axis vascular system (PO:0000039). [source: POC:curators]
Comment
Generally the largest and most prominent of the leaf veins. A leaf may have more than one primary vein. The central primary vein is the midvein (PO:0020139). Vein orders only apply to hierarchically branching vein patterns, not to dichotomously branching vein patterns, as found in some ferns and gymnosperms.