Definition - What does True Leaf mean?
True leaves are the leaves of a seed plant that contain vascular tissue. Unlike seed leaves, true leaves tend to be quite low on the stem and are normally produced first, after the seed leaves (cotyledons).
True leaves look distinctively different than the seed leaves. They tend to be hairier than their seed counterparts and tend to boast a more decorative shape. The true leaves appear above the cotyledons on the seedling, and appear as smaller versions of the plant’s adult foliage.
MaximumYield explains True Leaf
Prior to the appearance of true leaves, the plant produces cotyledons, which typically emerge from the soil upon germination. These provide enough nutrients and minerals to the plants until the true leaves start to emerge.
All of the leaves that emerge after the true leaves have appeared will look the same as the true leaves, rather than match the look of the seed leaves. Most plants don’t begin the process of photosynthesis until the true leaves start to appear.
While some growers prefer to pinch off the cotyledons once the true leaves emerge, some botanists recommend that you leave them intact to avoid accidentally damaging the stem. It is also advisable to wait until the appearance of true leaves before transplanting a seedling.