If you don’t mind me asking, why does your Meganium look so different?
Beetroot is a variegated pokemon! meaning some parts of her body do not produce chlorophyll! Variegation happens through natural mutation or viral infection and results in a reduction of chlorophyll in some of the plant's cells which causes the appearance of yellow, white, or rarely pink areas amongst green. Normal plants can show these same mutations as well! She showed no sign of it s a chicorita, but when she evolved into a bayleaf it scared the hell out of me! I thought she was sick and rushed her to a pokecenter. Nope, she was healthier than ever, just spotted!
Variegated pokemon need extra care and attention to their diet, as the lighter areas can no longer produce energy from the sun! Beetroot gets a vitamin d supplement every day, among other things. Also, Sickness, too cold or too hot weather, and prolonged stress can actually cause a variegated pokemon to permanently revert to their normal colors!! So a pretty spotted pokemon is a sign of good care!
My two new mystery pokemon here are good examples of different forms of variegation. Pinkie's leaves are have beautiful rose sections in her leaves where the chlorophyll is gone, with hard edges, while Finnegan has stripes of half-chlorophyll throughout and stripes of no-chlorophyll in the edges!
I believe this boy belongs to @veevee-power, i hope you don't mind me using your image! This guy is a good example of a mottled variegation, with spots of half and no chlorophyll scattered seemingly at random. He also exhibits patches of lightened color in his body, commonly seen with variegations as well, but considered a "flaw" in poke-plant shows.