I spotted an interesting plant at Rotary Gardens in Janesville, Wisconsin this past summer. It’s called popcorn cassia (it was Cassia didymobotrya, but now it’s Senna didymobotrya):
I didn’t know at the time, but I learned afterward that the leaves smell like buttered popcorn when crushed and some people detect a peanut butter scent from the flowers. That’s why this plant is also called popcorn senna or peanut butter plant.
The 12-to-18-inch flower spikes appear on plants that can get as tall as 5 or 6 feet depending on how much heat and water they receive. In tropical Africa the plants can get as tall as 25 feet. The buds are greenish-black and the flowers are a buttery, bright-yellow:
Popcorn cassia is a tropical plant so it performs best in full sun with moist, well-drained soil. The more water the plant receives, the taller it will grow. The flowers appear from July into September in Zone 5. It’s grown as in annual in all but Zones 9-11.
I haven’t been able to source the plant locally, but if I ever do I’d like to give it a try. And the next time I see one on display at a botanical garden I’m going to test out this popcorn/peanut butter claim for myself.