How to tell seedling varieties apart

For the most part, most heirloom tomato leaves look very much alike.  So, when starting out as seedlings it's very difficult to tell them apart. However, there are a few small visual cues that can help.  First is the leaf shape.  They are a kind of "potato leaf" design.  I found that the Black Krim and Black Plum are nearly identical.  The Russian Oxheart is also of the same design, but the leaves are a little more rounded and with more fringing, or spikes.  The Black Krim tends to have larger and slightly irregular shapes.  The Sara's Galapagos were a cinch to tell apart.  This plant looks astonishingly different from the others.