prolific South American aquatic weed having grasslike leaves and short spikes of white flowers; clogs waterways with dense floating masses

someone who takes the place of another person

someone who takes the place of another person

someone who takes the place of another person

someone who takes the place of another person

someone who takes the place of another person

someone who takes the place of another person

someone who takes the place of another person

in an alternating sequence or position

in an alternating sequence or position