Seeds were also present in ballasts of ships where soil was used to weigh down the vessels for stability on the ocean. Individual flowers have five or six pink-purple petals surrounding small, yellow centers. Each flower spike is made up of many individual flowers. There may be from 1-50 spikes per plant. Each mature plant can produce up to 2.7 million seeds each year.
Seed capsules appear on the lower part of the stalk while flowers at the top are still blooming.
This can be as early as July. Like tiny grains of sand, seeds are easily spread by water, wind, wildlife, and people. Germination can occur the following season, but seeds may lay dormant for several years before sprouting. Leaves are long and smooth edged. They are arranged opposite each other on the stalk in pairs at 90 degree angles.