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1997 WEED SCIENCE WORKGROUP REPORT
University of California, Davis
November 12-13, 1997
November 12-13, 1997
Appendix A
Waterplantain
(Alisma plantago-aquatica L.)[ALSPA]
SYNONYMS: A. triviale Pursh; A. subcordatum Raf, A. brevipes
Greene
GENERAL DESCRIPTION: Tufted native perennial marsh plant,
but behaves as an annual in California rice fields. Leaves variable,
mostly emergent, to 0.5 m, occasionally floating. Flowering stalks
taller than leaves, to 1.2 m. Considered weedy only in agricultural
systems. All plants in the waterplantain family have milky juice.
SEEDLINGS: Cotyledon elliptic to lanceolate, long-stalked,
typically floating. Stalk often red tinged. Immature leaves lack
blades or blades much reduced.
MATURE PLANT: Leaves basal, lanceolate to ovate, with long
petioles that sheath a short, bulbous stem base. Leaf bases truncate
to nearly cordate. Blades 5-20 cm long, 1-10 cm wide. Main veins
parallel, with tiny transverse veinlets.
ROOTS and UNDERGROUND STRUCTURES: Fibrous, all adventitious.
Stem base corm- like.
FLOWERS: June-July. Bisexual, arranged in whorled panicles,
with each branching node subtended by 2-3 leaf-like papery bracts.
Petals 3, separate, deciduous, white, rarely pink, ovate to rhombic,
with rounded tips. Margins smooth or minutely toothed (erose). Sepals
3, green, persistent, ovate. Stamens 6, arranged in pairs opposite
petals. Carpels numerous, separate, arranged in a ring on a flattened
receptacle.
FRUITS and SEEDS: Ring of achenes form fruiting head 3-5
mm diameter. Achenes sector- like, strongly compressed, 2-3 mm long,
longer than wide, each with a short ventral beak and rounded back.
Lateral walls generally thick and opaque. Air-filled tissues cause
achenes to float.
POSTSENESCENCE CHARACTERISTICS: Dead leaves decay rapidly
in water.
HABITAT: Grows in shallow water or mud; ponds, rice fields,
wetland margins.
DISTRIBUTION: Widespread native throughout CA, except Great
Basin, Mojave and Sonoran Deserts; to Canada, southeastern U.S.;
Eurasia, south, east, and northern Africa, and Australia. To 5300
ft (1600 m).
PROPAGATION/PHENOLOGY: Reproduces by seed. Seeds buoyant
for up to 2 months. Germination erratic because of mechanical dormancy
imposed by hard seed coat. Some seeds germinate after first winter
or dry season, others remain dormant for 4-5 years. Drying can induce
rupture of seed coat. Scarified seeds germinate readily. Seeds survive
frozen water or mud for several weeks.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Plants developing
from seed reach optimal size in shallow water (~7 cm) and decrease
linearly in size as water depth increases to 40 cm. Plants from
corms reach optimal size in deeper water (~20-40 cm).
SIMILAR SPECIES: Lanceleaved waterplantain (Alisma lanceolatum
With.)[ALSLA], an introduced perennial, generally has narrower leaves
(1-3 cm wide) with tapered bases and pink to purplish flowers. Typically
petals taper to a point (acuminate). Lateral walls of achenes thin
and translucent. Found in northwestern CA, northern Sierra Nevada
foothills, and the Sacramento Valley. To 1700 ft (500 m). Arrowhead
(Sagittaria spp) superficially resembles the waterplantains. For
a comparison, open this Leaf Table (1
page, 25 kb).
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