Leptomorph (runner / traçant)
are the thin and long rhizomes, having long and spaced internodes. The tip is often horizontally oriented, and is very hard for conquering new area. Culms are thicker than the rhizomes. Sometimmes a tip can move upwards and turn into a culm, but is more common one see the culms appearing at the rhizome sides, alternating from left to right (one side to another). These bamboos grow in forests, where one can walk through it. They spread fast, having invasive habits.

They are found generally among temperate species, as in the Phyllostachys genus.