Geoscience Reference
In-Depth Information
Figure 2-12.
Watercress (
Rorippa nasturium-
aquaticum
), an emergent wetland plant (see Color Plate
2-12). A member of the mustard family (Cruciferae), it is
a succulent, long-stemmed plant growing in tangled
masses or low mounds up to
30 cm (1 foot). The
leaves have a strong peppery taste; watercress is highly
valued for food l avoring and medicinal uses (Tilford
1997). Watercress absolutely requires clear, l owing
water with temperatures
∼
18 °C (65 °F), which means it
favors spring-fed streams. Flint Hills of east-central
Kansas, United States; photo by J.S. Aber.
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Figure 2-11.
Buttonbush (
Cephalanthus occidentalis
),
a shoreline wetland plant. It is a deciduous bush or
small tree that may exceed 3 m (10 feet) in height,
growing immediately beside lakes and streams,
sinkholes and swamps. Most distinctive are the showy,
white l ower clusters that are shaped like spherical
pincushions. Buttonbush is a member of the Quinine
family, and its inner bark was once used as a quinine
substitute. Lake Kahola, east-central Kansas, United
States; photo by J.S. Aber.
is underwater and may or may not be rooted
in the substrate. Only small portions, namely
l owers, rise above water level (Fig. 2-13).
• Submerged - Plants that are largely under-
water with few l oating or emergent leaves.
Flowers may emerge (briel y) in some cases
for pollination (Fig. 2-14).
Figure 2-13.
Egyptian lotus (
Nymphaea caerulea
) has
day-blooming l owers. The large round leaves are
l oating in a lily lagoon of the Okavango Delta,
Botswana. Photo courtesy of M. Storm.
Wetland vegetation is typically found in distinct
spatial zones that are related mainly to water
depth and salinity. As the groupings above
suggest, many wetland plants have rigorous
preferences for soil moisture and water depth
or salinity. Some occupy primarily shoreline
or emergent habitats, whereas others grow in
l oating or submerged situations (Fig. 2-15).
Thus, distinct zones of vegetation are developed
across the transition from dry, upland positions
into deep-water environments. Similar transi-
tional zones mark the change from fresh to salt
water along marine coastlines (Fig. 2-16) and
around inland saline lakes and playas.
