verticillata (L.f.) Royle][HYLLI][CDFA list: A][CalEPPC: Red Alert][Federal
Noxious Weed] Photographs Maps
Brazilian elodea [Egeria
densa Planch.][ELDDE][CalEPPC: A-2] Photographs
[Elodea canadensis Rich.][ELDCA] Photographs
DESCRIPTION: Submerged aquatic
perennials. Plants are genetically variable and highly plastic
depending on environmental conditions. Stems typically grow rooted
in the substrate, but fragment easily into free-floating pieces
that root at nodes. Fragments may start new colonies when carried
elsewhere. Brazilian elodea and hydrilla can aggressively
invade new aquatic environments, displace native aquatic vegetation
by forming dense stands or large sub-surface mats, and alter the
dynamics of aquatic ecosystems. Other detrimental impacts from
heavy infestations can include water flow impediment in waterways,
increased flooding, clogged pumps and boat propellers, diminished
water clarity, reduced use of lakes and waterways for recreational
activities, and economic loss.
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SEEDLINGS: Seldom encountered.hydrilla: Stalk below
cotyledon (hypocotyl) lacking. Rootlets whorled. Cotyledon sheath
2-5 mm long, glabrous, often whitish-green with purplish dots.
Cotyledon blade lanceolate, 6-8 mm long, 1-2 mm wide, +/- pinched
in just above the base (attenuate), margins smooth. Taproot and
first leaves develop simultaneously. First leaves compound. Leaflets
3-8, linear, 5-8 mm long, 0.5-1 mm wide, +/- sessile, tips acute,
margins minutely toothed.
sessile, whorled, linear to +/- lanceolate, often scale-like and
opposite on lower stems. The number of leaves per node is unreliable
for species identification. Margins minutely toothed, visible
with low magnification.
and UNDERGROUND STRUCTURES: Roots
slender, unbranched, in substrate grow to ~ 20 cm long. Certain
nodes on stems and stolons develop adventitious roots. Adventitious
roots of hydrilla and common elodea typically develop
only at nodes with dormant axillary buds or branches.
Flowers extend to the waters surface on a long thread-like
flower tube several centimeters long from an axillary spathe (fused
bracts). Petals, sepals, styles 3. Ovary inferior. Pistillate
(female) flowers often have staminodes (sterile stamens).
and SEEDS: Fruit production and seed set is typically low.
VEGETATIVE REPRODUCTIVE STRUCTURES:
CHARACTERISTICS: Plants decompose
rapidly. Stems of Brazilian elodea and common elodea
typically decline when water temperatures climb above 25º
C. Hydrilla and Brazilian elodea stems usually die
during periods of prolonged near freezing temperatures. Common
elodea may turn blackish and die-back during the cold season
or survive green and intact under ice in near freezing conditions.
or still water in ditches, sloughs, canals, rivers, ponds, lakes,
reservoirs; often in nutrient-rich substrates.
PROPAGATION/PHENOLOGY: All reproduce vegetatively. Seed is rarely produced
in California. Vegetative parts disperse with flooding, waterfowl,
and human activities, such as fishing and boating.
FAVORING/DISCOURAGING SURVIVAL: Removing and destroying stem fragments from recreational
equipment, such as boat propellers, docking lines, and fishing
gear can help prevent the spread of hydrilla and Brazilian
elodea. Suddenly removing dense canopies of hydrilla by
mechanical harvesting or herbicide treatment may stimulate turion
germination. Sterile triploid grass carp consume hydrilla and
are useful in aquatic systems where total removal of all submerged
vegetation is acceptable.
Grassy naiad [Najas graminea Del.] and southern naiad [Najas
guadalupensis (Sprengel) Magnus] are easily distinguished from the above
species by having sessile flowers and +/-whorled linear leaves 0.5-1
mm wide with sheathing bases that are mostly crowded on short
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