Virtually all of the frost hardy, timber and medium-size bamboos (30 feet and taller) have leptomorph rhizomes.  These rhizomes grow laterally through the soil surface, and all have the potential to spread rapidly.  In a mature grove, the culms arising from a bamboo with leptomorph rhizomes, usually have an open or diffuse habit.   Because of their ability to spread rapidly and indefinitely, bamboos with leptomorph rhizomes are commonly referred to as “runners” or “running bamboos”.