Sahara Mustard (Brassica tournefortii)
From the California Exotic Pest Plant Council 1997 Symposium Proceedings

The Sahara mustard is a coarse annual that was described from Iran, and is probably native to North Africa and Central Asia. It is now widespread in warm and regions of the world. This species has spread explosively across the lowlands of the Sonoran Desert, especially in places with sandy soils. In California, it was well established in the Coachella Valley by 1938 and was a contaminant in Hubam clover in the Imperial Valley in 1947 (Robbins et al. 1951). The earliest record for it in Arizona is 1957 (Mason 1960) while Sonoran collections date from 1966. By the 1970s it was widespread and well established in the lowland deserts of northern Baja California, southeastern California, southwestern Arizona, and western Sonora as far south as the Guaymas. It is especially common in sandy lowland habitats across the Sonoran Desert, including low dunes, interdune troughs, sandy flats, and sandy-gravelly washes.

Individuals of this species are amazingly variable in size, depending upon the availability of soil moisture. Drought-stressed plants can reproduce with leaves as small as 8 cm long. On sandy soils with sufficient moisture the leaves can grow to more than 50 cm long, giving the plant a 1 m spread, making it the largest herbaceous rosette plant in the region. It flowers from February to May. The small, pale flowers, anomalous petal blade patterns, and stamens that touch the stigma suggest a probability for self-fertilization.