Ginger is an example of rhizome..
The time to dig up iris is late summer when they are dormant.
Yes.Rhubarb is in fact a vegetable, one of the most unusual because it is eaten with sugar. The identity of rhubarb has vexed gardeners and chefs for years, so much so in fact, that a in 1947 a US court ruled it was a fruit.It's considered a vegetable here in UK as the edible stalks of the rhubarb plant grow from a sturdy rhizone (underground stem), and the best stalks are long, thin, vibrant pink and tender, and are the result of being force-grown in artificial darkness.