Stems:  Branching, with many prickles turned oppositely (retrorsely barbed) from the direction of the stem.

Flowers: Occur in small clusters at the ends of branches.   Flowers are white to pink in color and occur on the ends of leafless flower stalks (peduncles).

Fruit:  A brown to black nutlet.

Identifying Characteristics:  The arrow-shaped leaves and prickly stems helps to distinguish arrow-leaved tearthumb from most other aquatic shoreline weeds.  However, Tearthumb (Polygonum arifolium) is very similar in appearance and growth habit but has much larger hairy leaves with lobes that point outward unlike those of arrow-leaved tearthumb.

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