"High, Low and In Between"

We walked to an uncluttered patch of ground where there were wide spaces between the trees. The mid-afternoon sun, no longer eclipsed by bare branches, shone directly through. Dry brown leaves, with a few of their red and yellow brethren, adorned the brightened walkway. Sandy stopped before a patch of pink flowers with a cluster shape. Hoping to find the exact picture, I hastily thumbed past mallows and geraniums, roses and morning glory, sorrel and smartweed. Whereupon Sandy touched my forearm and advised: "I believe the Echinacea coneflower is under purple."
By the time I found it she was kneeling beside the coneflowers, which jutted from a patch of fish-shaped green leaves. From the head of each flower bulged perhaps 20 separate pink petals of nearly equal lengths, all radiating from a spiky center of dark orange. The petals tended to droop downward, except on the smaller, nascent flowers. Sandy caressed the underside of the flagging petals. "I've seen these flowers all over the place," I said. "I didn't know Echinacea came from them." 
Sandy said: "They are common, but I'm always drawn to them."
Further up the path she knelt again, amidst a patch of Black-eyed Susan. I tried plucking one by the stem and my fingers received a mild prick. "Sharp?" asked Sandy.
"Not sharp sharp," I said. "More like stubble." I crouched closer and fingered the stem's stubble. The petals were multiple shades of yellow: A burnished golden, like Sandy's hair, closer to the central node; a brighter, amber hue toward the middle; and a brighter, watercolor smudge of banana at the petal's tip. "Question for you," I said. "Why do some of these Susans - like these, over here - have only eight petals, while these - right here - have more than a dozen?"
"I don't know," said Sandy. "I suppose it just depends on how nature wants to cut the corolla."