A tumble**ed is the above-ground part of a plant that, once mature and dry, separates from the root and tumbles (rolls) away in the wind. Usually, the tumble**ed is the entire plant apart from the roots, but in a few species it is a flo**r cluster. The tumble**ed habit is most common in steppe and desert plants. The tumble**ed is a diaspore, aiding in dispersal of propagules (seeds or spores). It does this by scattering the propagules either as it tumbles, or after it has come to rest in a **t location. In the latter case, the tumble**ed opens mechanically as it absorbs water; apart from its propagules, the tumble**ed is dead. Although the number of species with the tumble**ed habit is small, several of these species are common agricultural **eds. Although thought to be native to Eurasia, several annual species of Salsola (family Amaranthaceae) that form tumble**eds have become so common in North America that they are a common symbol in **stern movies, where they are typically symbolic of desolation in frontier areas. Salsola pestifera became naturalized over large areas of North America after being imported from continental Asia often in shipments with agricultural seeds. Salsola kali is said to have arrived in the United States in shipments of flax seeds to South Dakota in the nineteenth century. Salsola tragus is an annual plant that breaks off at the stem base, forming a tumble**ed that disperses its seeds as it rolls on top of the ground. It seems to have been imported into South Dakota from Russia in 1870 or 1874 in shipments of flaxseed. It has become a noxious **ed that has spread throughout North America to inhabit suitable habitats which include areas with disturbed soils like roadsides, cultivated fields and eroded slopes, and in natural habitats that have sparse vegetation like coastal and riparian sands, semi-deserts and deserts. Salsola tragus is the correct name for the narrow-leaved, **edy representative of the S. kali aggregate found widely over North America. It is an extremely variable species with many races which vary in distinctness, some of these varieties in the past have been divided into subspecies or even separate species. Though it is a noxious **ed, Salsola tragus is useful on arid rangelands as a forage for livestock. Other members of the family Amaranthaceae that form tumble**eds include Amaranthus albus, native to Central America but introduced and **edy in Europe, Asia, and Australia; Amaranthus graecizans naturalized to North America from its native Africa; Amaranthus retroflexus; Corispermum hyssopifolium; Kochia; and Cycloloma atriplicifolium, which is called the plains tumble**ed. Atriplex rosea called the tumbling oracle or tumbling orach, is a member of Chenopodiaceae. In the aster family (Asteraceae), Centaurea diffusa (a knap**ed) forms tumble**eds. This species is native to Eurasia and naturalized in much of North America. Also in this family, Lessingia glandulifera, sometimes form tumble**eds, it grows in desert areas, chaparral and open pine forests of the **stern States of the USA and is usually found on sandy soils. In the legume family (Fabaceae), species reported to produce tumble**eds include some members of the genus Psoralea, and Baptisia tinctoria.