Which plant is a relative of the duck potato, has arrowhead-shaped leaves, and can have leaves as wide as 8 inches?

The broad-leaf arrowhead is the correct answer because it is indeed a relative of the duck potato and features distinct arrowhead-shaped leaves. This plant can have leaves that grow quite wide, reaching up to 8 inches across. The broad-leaf arrowhead is adapted to wetland environments and is often found in marshes and shallow waters, similar to the ecosystems where duck potatoes thrive. Its unique leaf shape and size make it easily identifiable, distinguishing it from other options in the list.

The cattail, while also a common aquatic plant, has a different leaf structure, characterized by long, narrow, grassy leaves, and does not have the arrowhead shape. Pickerelweed has broad leaves, but they do not possess the arrowhead shape associated with the broad-leaf arrowhead. Water hyacinth is known for its beautiful flowers and floating structure but has rounded, not arrowhead-shaped leaves. Therefore, the broad-leaf arrowhead stands out due to its specific leaf shape and relation to duck potato.