Geoscience Reference
In-Depth Information
A
B
Figure 6-19.
Bulrushes (
Scirpus
sp.). A. Great bulrush (
S. validus
) growing in proximity with B. Alkali bulrush
(
S. maritimus
). Photos by J.S. Aber; Stillwater National Wildlife Refuge, northwestern Nevada, United States.
frond, and some species have tiny roots dan-
gling below. Duckweeds are incredibly produc-
tive and are utilized as human food and feed
for domestic animals. They are major food
resources for birds, mammals, and i sh in
wetland environments.
Pondweeds
(
Potamogeton
sp.) - The pond-
weed genus is large and varied. All pondweeds
have rooted, submerged portions, and some
have l oating leaves as well (Fig. 6-23). Leaf form
shows considerable variations from large and
round to small, needlelike shapes. Underwater
and l oating leaves may be quite different in
form on the same plant. Identii cation of pond-
weed species is difi cult and requires a botanical
key. Pondweeds are among the most important
food plants for waterfowl in North America.
American white waterlily
(
Nymphaea
odorata
) - A popular water-garden plant, also
known as fragrant waterlily, this species is
native to eastern North America, but now is
found from Alaska to Florida (USDA Plants
2010a). The waterlily casts shade that cools the
water body, and it provides shelter and food
for small aquatic animals (Fig. 6-24). In eastern
North America, native people used the plant for
medicines and food. Where introduced, however,
it has a tendency to become invasive and is
listed as a noxious weed in some western states
(Washington Ecology 2010).
Giant waterlily
(
Victoria amazonica
) - This
spectacular wetland plant, known as the queen
of waterlilies, is native to shallow waters of the
Amazon basin in South America (Fig. 6-25).
Waterlily leaves may exceed 2 m in diameter, and
the lip is notched in two places to drain rain-
water. The huge leaf may support a person (up
to 135 kg), when the load is uniformly distrib-
uted (Davit and Cebrian 2007). The top surface
is covered with minute stomata that allow gas
exchange via aerenchyma with the roots. It was
i rst discovered in Bolivia in 1801 and created
quite a sensation when introduced into England
in the mid-nineteenth century.
