1987 Wetland Delineation Manual - The Wetlands Regulation Center

Wetland Delination Manual, 1987 91
APPENDIX C: VEGETATION
1. This appendix contains three sections. Section 1 is a subset of the regional list of plants
that occur in wetlands, but includes only those species having an indicator status of OBL,
FACW, or FAC. Section 2 is a list of plants that commonly occur in wetlands of a given
region. Since many geographic areas of Section 404 responsibility include portions of two or
more plant list regions, users will often need more than one regional list; thus, Sections 1 and 2
will be published separately from the remainder of the manual. Users will be furnished all
appropriate regional lists.
2. Section 3, which is presented herein, describes morphological, physiological, and
reproductive adaptations that can be observed or are known to occur in plant species that are
typically adapted for life in anaerobic soil conditions.
Morphological adaptations
Section 3 - Morphological, Physiological, and Reproductive
Adaptations of Plant Species for Occurrence in Areas
Having Anaerobic Soil Conditions
3. Many plant species have morphological adaptations for occurrence in wetlands. These
structural modifications most often provide the plant with increased buoyancy or support. In
some cases (e.g. adventitious roots), the adaptation may facilitate the uptake of nutrients and/or
gases (particularly oxygen). However., not all species occurring in areas having anaerobic soil
conditions exhibit morphological adaptations for such conditions. The following is a list of
morphological adaptations that a species occurring in areas having anaerobic soil conditions
may possess (a partial list of species with such adaptations is presented in Table Cl):
a. Buttressed tree trunks. Tree species (e.g. Taxodium distichum) may develop enlarged
trunks (Figure Cl) in response to frequent inundation. This adaptation is a strong indicator of
hydrophytic vegetation in nontropical forested areas.
b. Pneumatophores. These modified roots may serve as respiratory organs in species
subjected to frequent inundation or soil saturation. Cypress knees (Figure C2) are a classic
example, but other species (e.g., Nyssa aquatics, Rhizophora mangze) may also develop
pneumatophores.
c. Adventitious roots. Sometimes referred to as “water roots,” Adventitious roots occur
on plant stems in positions where roots normally are not found. Small fibrous roots protruding
from the base of trees (e.g. Salix nigra) or roots on stems of herbaceous plants and tree
seedlings in positions immediately above the soil surface (e.g. Ludwigia spp.) occur in
response to inundation or soil saturation (Figure C3). These usually develop during periods of
sufficiently prolonged soil saturation to destroy most of the root system. CAUTION: Not all
adventitious roots develop as a result of inundation or soil saturation. For example, aerial
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