Geoscience Reference
In-Depth Information
Figure 6-3.
Knees of swamp cypress (
Taxodium
distichum
). The exposed knees stand 20-40 cm tall and
allow gas exchange with the atmosphere. Widely
planted as an ornamental tree around ponds and
streams. Photo by J.S. Aber; Emporia, Kansas, United
States.
Figure 6-1.
Cattails are among the most common and
easily recognized wetland plants. Narrow-leaved cattail
(
Typha angustifolia
) at Stillwater National Wildlife
Refuge, Nevada, United States. Photo by J.S. Aber.
Figure 6-4.
Structural support for wetland trees. Red
mangrove (
Rhizophora mangle
) lives in shallow marine
water of bays and estuaries. The tree is supported by
curving stilt (or prop) roots that are covered with
lenticels for air exchange. Florida Keys, United States.
Photo by J.S. Aber.
Figure 6-2.
Black mangrove (
Avicennia germinans
)
grows in the saline tidal zone, inland from the open
sea. Breathing roots, called pneumatophores, grow up
from soil for air exchange. A single tree may generate
up to 10,000 pneumatophores (Newfoundland Harbor
Marine Institute 2010). Photo by J.S. Aber; Florida Keys,
United States.
ported by water; they have no need for a rigid
or self-supporting structure as do emergent
plants. When these plants are removed from
water, they typically collapse (Fig. 6-5).
Chloroplasts are the organelles in which pho-
tosynthesis takes place. Strong radiation may
damage the chloroplasts in plants exposed to
direct sunlight and, thus, chloroplasts are
embedded deeply in emergent leaf tissue. For
submerged plants, however, light is diffuse and
function similar to the l ying buttresses of Medi-
eval cathedrals, namely to hold the plant upright
(Fig. 6-4). Stem hypertrophy (trunk buttress) is
formed by lower-density wood that may also
facilitate oxygen exchange. Submerged plants
likewise have enlarged air spaces in their leaves,
stems and roots. The plants are buoyant because
of the gas-i lled chambers and are partly sup-
