This alliance includes ruderal vegetation with a predominance of biennial and perennial species, often forming the initial stages of succession on anthropogenic substrates. It occurs on shallow soils with a high content of gravel or dross, which are dry and poor in nutrients. This vegetation type includes several symbiotic nitrogen-fixers of Fabaceae in its composition. Most stands are rich in species. This vegetation type existed already in the Middle Ages, but it spread extensively during the 20th century due to the development of road and railway network, building construction and mining activities. It contains a high proportion of both archaeophytes and neophytes. In the Czech Republic this vegetation type is most common in warm areas, but some types can also occur in cooler areas at higher altitudes.