Here's why:

* Dicots have two cotyledons (seed leaves) in their embryos. Arugula seeds have two distinct seed leaves when they germinate.

* Monocots have only one cotyledon.

Additionally, arugula exhibits other characteristics of dicots, such as:

* Net-like leaf veins: Arugula leaves have a distinctive network of veins.

* Taproots: Arugula has a single, strong taproot.

* Flower parts in multiples of four or five: Arugula flowers have four petals.