I’m not seeing any shadows cast by the flower.
Here’s a few things you can check. Look in the object data for the flower (Properties tab looks like a cube). Go down to Ray visibilty and make sure Shadows is checked.
Check Light properties for your Sun Lamp. make sure box for “Cast shadow” beside size is checked.
Then play around with the size of your lights (Slider box for Size on light tab for Sun, actual physical size of emitter planes). Depending on how physically large the planes are or how large you have the sun size set to, they may be washing out each others shadows.
Just for testing purposes I’d turn off the two emitter planes and try the sun by itself in a quick test render to see if it’s casting shadow. Turn the size down if needed.
For sun lamps the clarity of shadows they cast is dictated by the Size you have set for them, distance from the object is irrelevant. From my experience if you set a sun’s size to more than about .3 the shadows tend to be non-existent. Set size to 0 gives perfectly crisp shadow edges, as you increase size it the edges become less defined to the point where the shadow eventually will disappear completely.
For planes set as emitter the physical size and strength of the emitter effects the type of shadow. Small size with a high strength will give much crisper shadows than a large plane set to a lower strength.
Play around with these numbers to see what you can get.