Aquatic Plants of Colorado

Aquatic plants are often overlooked when one pictures the flora of Colorado. However, these unique plants are widely dispersed from the plains to the subalpine and are vital, essential components of the wetland ecosystem. Aquatic plants provide food for wildlife, a home for many aquatic insects and fish, and wetlands in general are important in preventing erosion. When most people think of aquatic plants, they picture the awe-inspiring sight of a subalpine lake covered in beautiful yellow-blooming water lilies. Yet, there are many more aquatic plants in Colorado that go unnoticed everyday.

About now, you might be asking yourself, "Well, this is nice, but what is an aquatic plant?". Aquatic plants, or hydrophytes, comprise those species of plants that are physiologically bound to the water to complete their life cycles. Aquatic plants can be either submerged, floating-leaved, or emergent. Submerged aquatic plants have all photosynthetic parts of the plant submerged under water. The term photosynthetic parts is used to describe these plants because they can bloom above the water's surface. These plants are usually attached to the bottom of a body of water, but they can be free-floating as well. Examples of submerged aquatic plants include many Potamogetons or pondweeds, Myriophyllum, and Ceratophyllum.

Floating-leaved plants have their leaves floating on the surface of the water. Some plants with floating leaves also have submerged leaves, but they are still considered floating-leaved aquatics. Aquatic plants which exhibit this floating-leaved form include water lilies and duckweed. Emergent plants have some parts of the plant in contact with the air above the water's surface. Examples of emergent aquatic plants include bur-reeds and Sagittaria or Arrowhead.

In Colorado, aquatic plants can be found from the plains out east to subalpine lakes high in the Rocky Mountains, in a wide variety of water bodies. Aquatic plants grow in ponds and streams, peat bogs, and abandoned gravel pits. Typically, ponds support a more diverse variety of aquatic plants than streams do because there are more nutrients available, and the water moves at a much slower pace in ponds. In addition, plant growth in ponds is a reflection of the conditions of the body of water including water depth, nutrient availability, soil type, and geology.

Lakes and ponds found at the highest elevations generally support little to no aquatic plants because the water is too cold, the sides can be very steep, and few nutrients are available for plant growth. Mountain tarns or pools are often steep-sided with gravelly bottoms. Because these lack many nutrients, vegetation is sparse. However, Quillwort can sometimes be found in these mountain tarns or pools because it is able to tolerate the acidic conditions produced. Waterlilies, or Nuphar luteum ssp. polysepalum is one aquatic plant that is found in high mountain lakes. However, it is a mystery why this plant appears in some lakes but is absent from others that exhibit the same conditions. In general, ponds which support the best plant growth have neutral or alkaline water, and are shallow to let in more light for better aquatic plant growth.

There are several distinct zones in a pond or lake, which are in turn each characterized by their own species of plants. The zone surrounding the perimeter or shore of the body of water is called the swamp zone. This zone usually contains shallow water, but it can dry out. Plants typical of this zone include many wetland species such as grasses, sedges, cattails, rushes, and horsetails. The next zone of plants is the emergent zone. This zone occurs in deeper water and generally does not dry out. Plants in this zone are rooted in the mud with the bottom half of the plant in the water and the top half of the plant emergent. Typical plants of the emergent zone include emergent aquatic plants such as Arrowhead and Bur-reed.

The floating-leaved zone is the next zone, and this zone occurs in deeper water so that it does not generally dry out. As you might have guessed, floating-leaved aquatic plants are found in this zone. The last viable zone for aquatic plant growth in a body of water is the submerged zone. Submerged aquatic plants are found in this zone, but free-floating aquatic plants can also be found here. Approximately 6.6 feet is the depth to which aquatic plants can grow.

As in other ecosystems, wetland and aquatic plant ecosystems possess their own unique ecology and successional patterns. Succession in ponds is marked by a sequence of plant communities that gradually replace each other until a pond matures and eventually disappears. In fact, the stages of succession in a body of water can be seen in the zonation of plants around it. Succession begins with pioneer plants that colonize the body of water. As these plants die, they release organic nutrients into the water thus enabling more plants to become established.

Sediment gradually accumulates on the bottom of the body of water from the organic debris, which allows even more plants to become established. As the process continues, the body of water begins to diminish in circumference as the shore line begins to encroach on the middle of the pond. As this sediment builds up over time, the pond gradually changes into a swamp or marsh. The vegetation keeps encroaching to the center of the body of water, until it replaces the pond completely.

In addition to having their own ecological and successional qualities, aquatic plants also possess many unique adaptations which allow them to survive in an aquatic habitat. In fact, the submerged leaves of aquatic plants have no stomates for gas exchange. So instead of absorbing CO₂ through stomates, submerged aquatic plants absorb this vital gas in solution from the water.

One of the main problems facing submerged aquatic plants is the ability to obtain oxygen. Because they are submerged in water, these plants cannot obtain this vital gas through stomates like terrestrial plants. Therefore, the stems, roots, and leaves of submerged aquatic plants also possess intracellular spaces called aerenchyma that supply oxygen to the rest of the plant. These gas chambers act as an internal ventilation system and thus allow for the diffusion of oxygen to lower parts of the plant.

Submerged aquatic plants utilize living in the water to their fullest advantage. Because these plants are in no danger of drying out, the leaves have little to no cuticle on the surface of their leaves. In addition, the stems of these plants are limp and delicate with little strengthening tissue because they utilize the water for support. Also, the finely dissected leaves of submerged aquatic plants offer little resistence to the water.

In order to survive for further generations, a plant must be able to reproduce. Aquatic plants are no exception to this, and they have devised several unique ways of producing new offspring. Some plants such as Ceratophyllum or Coontail reproduce utilizing unique structures called winter buds. The winter bud is a dense mass of foliage produced on the top portion of the plant, and it contains an embryo plant. The winter bud is also very densely packed with food reserves for the embryo plant. The winter buds develop in the fall and become detached from the parent plant, sinking to the bottom until spring when they will form a new plant. Yet other plants such as Elodea canadensis use the water's surface as a medium for carrying pollen to the stigma of the plant.

No discussion of the adaptations of aquatic plants would be complete without mention of the carnivorous nature of the Bladderworts or Utricularia sp. These plants have tiny bladders attached to finely dissected leaves which trap and digest very small animals such as Paramecium. This enables the plant to obtain essential nutrients for growth that would otherwise not be found in high mountain ponds and lakes.

Now that your interest in aquatic plants is sparked, you might be wondering where some good places to find a few of these plants are. There are actually quite a few places just around Ft. Collins that offer excellent opportunities to observe or collect aquatic plants. The Spring Creek Trail running through Ft. Collins has a wonderful selection of aquatic and wetland plants along it. For example, behind the Holiday Inn off Prospect, one can find anything from Duckweed and Watercress to Callitriche or Water-starwort. Also, the trail just off of College across from Bank One offers a selection of Potamogeton and Zannichellia. Another good spot by Ft. Collins is a small ephemeral pond on the way up to Horsetooth Mountain Park. In it you might discover a couple of Potamogetons, some Elodea, or anything else that the local wildlife has transported in.

If looking at water lilies is more along your line of interest, the Denver Botanic Garden has a large selection of these plants including the giant amazon water lilies. In addition, Red Rocks Lake in the Brainard Lake Recreation Area by the town of Ward has an impressive display of native water lilies. A hike in Rocky Mountain National Park to Ouzel Lake in the wild basin area offers a chance to see a small pond covered in water lilies and surrounded by Buckbean. A word of warning in this area, however, once you start looking for aquatic plants, you won't be able to stop!

References and Additional Information:

Caduto, Michael. 1990. Pond and Brook. Hanover, NH: University Press of New England.

Muenscher, Walter. 1944. Aquatic Plants of the United States. Ithaca, NY, Comstock Publishing Co., Inc.

The Center for Aquatic Plants: http://aquat1.ifas.ufl.edu

Harrington, H. D. 1967. Edible Native Plants of the Rocky Mountains. The University of New Mexico Press.

Weber, W. A. 1976. Rocky Mountain Flora. Boulder, CO: Colorado Associated University Press.

Harrington, H. D. & Matsumura, Y. 1955. The True Aquatic Vascular Plants of Colorado. Colorado Agricultural College, Fort Collins.

Do You Know?

There are about 45 aquatic plant species in Colorado. The next time you find yourself in the great outdoors, try locating these aquatic plants:

EMERGENT SPECIES:

Persicaria coccinea

Scarlet Smartweed

Sagittaria latifolia

Arrowhead

Sparganium angustifolium

Bur-reed

Menyanthes trifoliata

Buckbean

FLOATING-LEAVED SPECIES:

Lemna minor

Common Duckweed

Nuphar luteum ssp. polysepalum

Spatterdock, Cow Lily

Potamogeton gramineus

Pondweed

Callitriche palustris

Water-starwort

SUBMERGED SPECIES:

Ceratophyllum demersum

Coontail

Ranunculus trichophyllus

Water Crowfoot

Potamogeton pectinatus

Sago Pondweed

Utricularia vulgaris

Great Bladderwort

Elodea canadensis

Canadian Waterweed

Zannichellia palustris

Horned Pondweed

Myriophyllum exalbescens

Water-milfoil