Lavender Sorrel is a perennial herb that originated from South America. It is an introduced ornamental plant but is now commonly found as a weed. Its lovely purplish-red flowers appear from March to December. As its leaves contain a large amount of oxalic acid and taste sour, it is also commonly called ‘sourgrass’. Sorrel (Oxalis corniculata), another plant of the same genus, is a native plant that has yellow flowers.