The tallest amaranth grew over 23 feet tall and was listed in the 2009 Guinness Book of World Records as the tallest Amaranthus. Amaranth pictured is a Amaranthus australis or commonly called the 'giant amaranth' or 'southern amaranth'. This amaranth is an annual and a native of the south eastern United States and grows to an enormous size. Capable of reaching nearly 30 feet tall in the wild. These plants can produce enormous hollow stalks that I've seen as large as 6 feet in circumference. Grown in Ewing, NJ in 2007.