Flowers are plants which can earn you cash are listed here.
Corn- 10 coins - found in Fillmore's Fields only, they are found in large groups
Blue Cactus Flower- 20 coins- Found mostly in Willy's Butte and several can be found in Downtown Radiator Springs
Orange Cactus Flower- 50 Coins- Found in Willys Butte only, there are several found here and they are so far the second most expensive flower
Pink Cactus Flower- 20 Coins- Found in Willys Butte only, there are the most common flower found in Willy's Butte
Golden Cactus Flower- 10 coins- Willy's Butte and Downtown Radiator Springs, 4 total can be found in Willy's Butte and 5 - 7 in Downtown Radiator Springs, note that the ones in Downtown Radiator Springs grow rapidly.
Totally Sweet Cactus Fruit- 70 coins -Found in Willys Butte only, they are the most expensive flower that can be found and there are about 3 - 4 in Willy's Butte.