I started by wetting the paper and dropping in warm yellow at the top and cool yellow at the bottom letting it move around the paper.  After that dried, I started working on each separate bract.  I dampened the individual bract, making it less wet than when I dropped color in the background.  Less wet means I have a little more control and can guide the paint.  I started moving around doing areas that do not touch.

This picture was taken in class with a cell phone so the colors and values are off.

I continued working around the head of the artichoke making sure I don't work next to an area that is still wet.  I also started with second passes on a few bracts working on adding more color and value in the medium and dark areas where needed.  I am building to the darks.  I also showed lifting with a soft brush especially on the blue green too dark bract on the right.  I also use lifting with a soft brush to soften edges when needed.  I showed scrubbing with a stiff bristle brush, one I made myself by cutting the bristles at an angle.  Scrubby brushes are also available for purchase.  I have always made my own.  I wet the scrubby and rub it over the are I want whitened.  Remember, I usually do this at the end of a painting as scrubbing changes the surface of the paper and is difficult to paint around.  I will use glazing to adjust colors as needed.  I mixed the green I used with my green blue (DS pthalo blue green shade) and my warm yellow (DS permanent yellow)