Seedlings

It can be quite difficult to determine plants by their vegetative parts. In the botany course I followed I was taught to only look at the reproductive parts of the plant, because the other parts were quite hopeless in trying to determine a species and all professional plant guides were based upon reproductive parts.

• Sexual reproductive parts are those involved in the production of seed. They include flower buds, flowers, fruit, and seeds.
• The vegetative parts include leaves, roots, leaf buds, and stems.

And it is even harder to determine plant species of seedlings, because they have not reached their final shape yet. But this one was easy because I could cheat:

27 march 2011 - photograph

4 april 2011 - photograph

I know the place where this plant grows and I know what kind of plant it is. It is made easy because this is part of my nature near home:

After long experience I am convinced that the best place to study nature is at one's own home. [...] The wild creatures about you become known to you as they cannot be known to a passer-by. [...] You will find she has made her home where you have made yours, and intimacy with her there becomes easy.

So I know from personal experience that this seedling is Impatiens parviflora - Small-flowered Touch-me-not).  

Sources:

Botany - plant parts
Nature Near Home and Other Papers by John Burroughs
Impatiens Parviflora - Wikipedia