Here's why:

* Phenotype: This refers to the observable traits of an organism, resulting from the interaction of its genotype (genetic makeup) with the environment.

* Physical characteristics: These include things like:

* Color: Flower color, leaf color, stem color

* Size: Height, width, leaf size

* Shape: Leaf shape, flower shape, fruit shape

* Texture: Leaf texture, stem texture

* Presence or absence of structures: Spines, thorns, petals, etc.

You can't directly observe the genotype (genes), so observing the physical characteristics is the easiest way to determine the phenotype.