Toxic plants can grow in and around water. Although many toxic water plants are better suited for growth on the banks of rivers, ponds and lakes, they can sometimes adapt to growth in shallows. Some of these plants are highly toxic, while others have parts that are only toxic during certain parts of the growing season.
Arrow arum (Peltandra virginica) is an aquatic plant that is poisonous. This freshwater plant grows only in water, and will not grow once an area has dried out due to a drop in water levels or drought. It has large, triangular leaves that rise above shallow water. The leaves have protrusions near the stems that make them look like arrows, hence their name. They produce a fleshy, cylindrical inflorescence that eventually turns into a seed pod that drops its seeds into the marsh. The plant can cause pain in the mouth, throat and stomach. Sensitivity varies, depending on the size of the person or animal ingesting this plant. Toxicity can vary, depending on the time of year and the part of the plant ingested.
Water hemlock (Cicuta maculata) is the most poisonous plant in North America. Although it usually grows in bogs, swamps and along freshwater shorelines, it is tolerant of flooding and can sometimes grow in the temporary shallows that form after hard rains or floods. Another name for this plant is spotted cowbane. When flowering, it features 1/8-inch-wide flowers that form umbrella-like clusters that can grow to between 2 and 4 inches in diameter. Water hemlock has a hollow stem and its leaves have jagged edges which may have a red tinge around the perimeter. They grow to 4 inches long and 1 1/2 inches wide. This plant grows to between 3 and 6 feet tall. This plant is so poisonous that handling any part of the plant is not recommended.
The cardinal flower (Lobelia cardinalis) is not as poisonous as other flowers. Although this flower is common in many areas, its blossoms are often over-picked resulting in only its green leaves being visible. The showy red flowers are long and tubular. Although may insects try to get in to the flowers, their length means that their primary vector of pollination is through hummingbirds. Although all parts of the flower, including the root, are poisonous, the plant is safe to handle. Plant toxicity emerges only after eating large quantities of the herb or root. Parts of this plant, taken in small quantities, is recommended by Native American traditional medicine. Symptoms of poisoning include nausea, vomiting, diarrhea and lethargy. Cardinal flowers are perennials that grow to between 1 and 6 feet tall. Cardinal flowers grow both on dry land in wet soils or in shallows that have been temporarily flooded.