sentences:  Recent genetic research has shown that the genus is paraphyletic unless the monotypic genus "Stenosiphon" is included within "Gaura", increasing the number of species in the genus to 22.They are annual, biennial or perennial herbaceous plants; most are perennials with sturdy rhizomes, often forming dense thickets, crowding or shading out other plant species.They have a basal rosette of leaves, with erect or spreading flowering stems up to 2 m (rarely more) tall, leafy on the lower stem, branched and leafless on the upper stem.