Here's why:

* Dicots have two cotyledons (seed leaves) in their embryos.

* Monocots have only one cotyledon.

Sunflowers have two cotyledons, and they also exhibit other characteristics of dicots, such as:

* Net-like veins in their leaves

* Taproot system (one main root with smaller roots branching off)

* Flowers with petals in multiples of four or five

So, based on these traits, a sunflower is definitively classified as a dicot.