If you did not use a flash or any other light source, why is there harsh shadowing between the petals indicating that a strong light source was used just above the camera?

I am a photographic professional and I know for a fact that this picture was not taken under the same conditions as the first two to which you compare.

In a situation where you have a dark and overcast sky as the only light source there would be no harsh shadowing between the petals.

Light from the sun is scattered by thick clouds (such as in your photograph), producing a diffused lighting pattern which is inherently soft and does not produce harsh shadows.

Although you may think that this last picture was not taken with a flash or another light source close to and above the lens, I can quite categorically assure you that it most certainly was!

Although I would agree that ANY dedicated Canon digital camera above a G3 would be greatly superior in image quality (even on full auto) to ANY mobile phone camera.

As for Nikon digital cameras, I have had experience with their 'compacts' including the Coolpix 5000 and quite frankly I was greatly disappointed with the quality or should I say lack of produced by cameras from this manufacturer.

Current Nikon cameras can not compete with the quality of any Canon EOS digital full stop.