Sow thistle, commonly called Milk Thistle in my part of the world, the Sonchus genus, grow in many somewhat different shapes and sizes – some softer and some rather rough and prickly.  We use them all, simply adjusting the use to the type of thistle.  The softer ones get used in salads, eaten raw in sandwiches or other similar ways.  The rough ones are generally added to green smoothies or included in well-cooked dishes such as a vegetarian pasta sauce.  The message is – Don’t be afraid to use them all, irregardless of how tough or prickly the particular sow thistle is.