[bvw]

Plants store energy, with a storge mechanism -- or even a digestive adaptation -- they could. Any backing for your hypothesis they they could not?

[WildTurkey]

Plants store energy, with a storge mechanism -- or even a digestive adaptation -- they could. Any backing for your hypothesis they they could not?

Maybe one species did and it turned out to not be an advantage over other plants so that species died out.

Evolution does not focus on what can or can not happen, it focuses on what is here and how it evolved from earlier processes.

[general_re]

Well, first, you can't store energy without first gathering it somehow. Beyond that, it's not a hypothesis, it's purely a numbers problem - it's mathematically inescapable. The average amount of solar energy that hits the surface of the earth is 3000-4000 kcal/m²/day. Plants have a photosynthetic efficiency of 1-3% - that is, they are able to convert 1-3% of the solar energy they receive into useable chemical energy. So, for a 1 m² plant, it can produce, at best, 120 kcal per day (3% of 4000 kcal) of useable chemical energy. You, being a normal human, probably burn through 1500-2000 kcal per ordinary day, or if you're exceptional, potentially far more - Olympic athletes in training can easily burn through 10-12,000 kcal per day. Anyway, the long and the short of it is that photosynthesis just doesn't produce the juice you need.