Small White

Female.

No reason for appologies ;-).... I just passed by a wonderful example of a Large to show the differences between the two. If you can't see this spot clearly it is sometimes very tricky to get an ID.

Sorry for the delay, have been absent. I see the difference now, appologies for the mistake. I do indeed have a photograph of a Large White, it just is not this one really. Thank you for the correction.

In this shot you can see the differences between Large and Small White. Please, look at the black triangle at the forewing and compare with yours.
http://www.projectnoah.org/spottings/139...

I apologize, but it is for sure a Pieris rapae and the female. My arguments: Usually smaller than the large white, however, size is not (always) a reliable criteria. Yours looks small compared to the leaves. But a large Small White might be larger than a small Large White and viceversa. The only valuable criteria for separating Brassicae from Rapae is the black part at the tip of the forewing. Take a look at the first black spot: If the black triangle (which is in Brassicae a real triangle-shaped patch, in Rapae more a "rectangle" with a horizontal line parallel to the upper margin) is extending BELOW this spot, meaning below or til the 5th vein it is Brassicae, if the black patch is ABOVE the first spot, which would mean about the 3rd vein, than it is Pieris rapae.
I just added the US link for showing the "same" features like in your picture. Brassicae is NOT found in US and Rapae is the most common White in Europe, specially this year, at least in my aera, which is not too far away from yours. I have not seen many, if any, Brassicae in Switzerland this year. Unfortunately I have not seen much butterflies anyway this year (too cold winter). I hope you had a better butterfly time in Portugal!
I added some links to compare:
Rapae:
http://www.leps.it/indexjs.htm?SpeciesPa...
http://www.schmetterling-raupe.de/art/ra...
Brassicae:
http://www.leps.it/indexjs.htm?SpeciesPa...

bayucca, I'm pretty sure it is a Large White, I understand it is rare in North America but it is quite common here in Europe (which is stated in the link you provided), nevertheless thank you for your suggestion.

It is the Small White, not the Large one.