I wouldn't define hard grown by the sun. Any native habitat plant is almost by definition a hard grown plant and a great many of those grow in shady, swampy, temperate rainfall, rainforest, forest, as well as in sun. I think the distinguishing characteristic is the care they get which modifies the conditions they grow in naturally. I'm with Daisy in that I think there are many, many shades of grey in the definition. Plants have their own ideas, so some actually thrive outside their natural habitats.
