You will notice that we often mention "true leaves" in our information on how to grow our seeds. So what are we talking about?
The first "leaves" to appear are not leaves at all, they are known as Cotyledons. They are part of the seed's embryo and are commonly known as seed leaves. Cotyledons provide nutrients to the seedling until its true leaves unfurl and begin the process of photosynthesis.
It is for this reason we state to wait until the true leaves form and the seedling has established before transplanting.
Below is a Russel Lupin seedling showing its Cotyledons and its first true leaf.