Which scientist proposed a classification system exclusively for plants?

$Statement-1$: Linnaeus classified plants into trees,shrubs,and herbs based on morphological characters.
$Statement-2$: Aristotle divided animals into two groups: $Anaima$ (animals without red blood) and $Enaima$ (animals with red blood).

Find the odd one out regarding the classification systems.

Why are the classification systems changing every now and then?

Provide a brief overview of the five-kingdom classification proposed by $R$.$H$. Whittaker.

Who classified plants into $24$ groups based on their sexual characteristics?