• Hundreds of plants qualify as endangered species in North America. Even more are endangered worldwide. Water plants are not immune to this problem; changes in water quality or bank conditions can affect them severely. Sometimes, it is difficult to tell how endangered a plant is until it's truly a problem because many of these aquatic plant species look similar to other species that may be flourishing.
  
  

Water Pennywort

• The water pennywort, scientific name Hydrocotyle ranunculoides, grows mainly in swamps, marshes and ponds. It has long stems, which float on top of the water, and are attached to the edges of its rounded leaves. The species prefers sunny areas, or areas with only slight shade and slow moving or stagnant water. Its thick system of stems and leaves can provide homes for small invertebrates. In the late summer to early fall, small flowers will blossom on the stalks. When the flowers fade, they're replaced by a small fruit, which can float on water, allowing the plant to spread to new areas. Despite how aggressively the plant is capable of spreading, it is endangered in much of North America. However, it is an invasive species in Australia and considered a nuisance.
  
  

Parker's Pipewort

• The parker's pipewort plant, scientific name Eriocaulon parkeri, grows in mud that's mostly submerged in water, tidal marshes or other areas of brackish water. It has a high tolerance for water chemistry variation but currently lives only on the east coast of Canada and in a handful of states on the east coast of the United States. It has tall, delicate flowering stalks, grass-like leaves and tiny white flowers. The plant flowers from late July to September, producing small, encapsulated seeds. The plant has been threatened because of changes in hydrology due to dams, beavers and other blockages as well as changes in its habitat due to toxic dumping, pollution or construction of docks or piers. As of 2010, the plant remains in very few places, with most sightings occurring in Maine. A few organizations are conducting research to help conserve this plant, but not much is actively being done.
  
  

Heart-Leaved Plantain

• The heart-leaved plantain is also known as the king-root plantain, or by its scientific name, Plantago cordata. It is a perennial, semi-aquatic plant that grows mainly in the central and eastern regions of the United States and Canada. It has heart-shaped leaves with prominent veins. When flowering, which starts in mid-April, the plant grows flowering spikes up to two feet tall. The plant grows at the edges of streams that run through heavily wooded areas. It requires very specific and predictable water conditions, and reacts poorly to change. It's considered rare in nearly all locations as of 2010, and many of its Midwestern populations have died out. It is most common in Missouri. The plant is threatened by habitat loss, encroaching urban environments, water pollution and increased water flow in its areas of choice. It also struggles because of deforestation or changes in erosion patterns.