It outcompetes the native flora. Birds are fond of the blackberries and thus spread the seeds over large areas. Pokeweed - Phytolacca americana Pokeweed is a native perennial that can grow up to six feet tall. Although the plant is poisonous, especially the roots and berries, the springtime leaves can be boiled and eaten as a green. The berries were used by the settlers in the New World to make one of the first natural inks.
Birds feed on the berries and sometimes act drunk afterwards.
Smartweed - Polygonum sp. In the buckwheat family, many smartweed species are native to the U.S. and grow in moist areas. The flowers are pink, rose and white, blooming from June through September. American smartweeds were taken to England in the 18th century to use as ornamentals. Several species from Asia, including the ornamental Polygonum cuspidatum, are aggressive and invasive and are very difficult to eradicate.