These architectural plants are extremely drought tolerant. The dasylirions form a genus of 18 species, all from the desert areas of southern USA and Mexico, where they are known as Sotol or Bear Grass. Most form a short trunk topped by an almost spherical head of leaves. The leaves are very narrow about 1m long with very small teeth along the margins. The trunk of Dasylirion longissimum grows to a height of 4m. Old leaves are retained on the trunks leaving a grass skirt effect. In summer they produce a huge flower spike up to 4m high covered in creamy white flowers, similar to yucca.