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Poison Hemlock
Apiaceae (=
Umbelliferae), the parsnip family
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Background
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 Poison
hemlock is native to Europe. It contains highly poisonous alkaloids toxic to
all classes of livestock and humans. It has poisoned many who have mistaken
it for parsley. Poison hemlock is often found on poorly drained soils,
particularly near streams, ditches, and surface water.
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Description
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 Poison
hemlock is a biennial that grows up to 10 feet
tall. Stems are stout, hollow, ridged, and mottled with purple spots. Leaves
are shiny green, 3 to 4 times pinnately compound, and
clasp the stem at the
obvious nodes. Crushed foliage has a disagreeable, mousey odor. Flowers are
small, white, and borne in umbrella-shaped clusters about 3 inches across
in early summer. Seeds are ridged and flattened, with 2 seeds borne
together. The plant has a thick, white
taproot.
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Distribution
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 It
grows throughout the U.S. except from eastern Montana to northeastern
Minnesota and south to Nebraska. It has an extensive presence in Idaho. |
Control
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A biological control agent (a
defoliating moth) provides good to excellent but inconsistent control.
Herbicides are also available.
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© 1999 University of Idaho:
Text and photographs for these pages from Idaho's Noxious Weeds, by
Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita
and Larry W. Lass).
Please contact: Ag Publishing, University of Idaho, Moscow,
Idaho 83844-2240; 208 882-7982 visit the Resources for Idaho website at
http://info.ag.uidaho.edu, for more information about this or other
publications.
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Alternate-leaves
that are arranged singly up the stem; not opposite each other.
Annual-plant that germinates, flowers, seeds, and
dies during one growing season.
Anther-structure
in a flower in which pollen is formed
Auricle-lobe-like
structure at the collar of a grass leaf.
Awn-slender bristle
at the tip of grass seed structures.
Axil-the angle
formed between a leaf and a stem.
Basal-at the base
of a plant or plant part.
Biennial-plant
that germinates in one growing season, then flowers, seeds, and dies during
a second.
Bract-leaf-like
structure at the base of flowers or leaves.
Calyx-all the
flower leaves together, normally green in color.
Clasping leaves-leaves
that appear to wrap around the stem at their base.
Compound leaves-leaves
with 2 or more distinct leaflets.
Cotyledons-the
first leaf-like structures that appear after germination; seed leaves.
Crown-the
structure formed where leaves, stems, and roots grow together.
Dissected-deeply
and repeatedly divided into smaller parts.
Entire-not
toothed or otherwise cut.
Glumes-the 2
bracts surrounding a grass spikelet.
Head-a group of
flowers borne tightly together.
Leaflets-leaf-like
structures within a compound leaf.
Ligule-the structure at
the collar of a grass leaf between the sheath and the stem.
Linear-long,
narrow, and slender.
Lobed-a cut into a
leaf from the edge toward the center; greater than toothed, but not quite
compound.
Margin-the edge
of a leaf.
Membranous-thin
and flexible, usually not green.
Midrib-the center
and usually most prominent vein on a leaf.
Nodding-a flower
that is not pointed upward, but bent downward or sidewise to the stem.
Opposite-leaves
situated directly across the stem from each other.
Ovate-egg shaped
in outline.
Panicle-a
much-branched inflorescence.
Perennial-a
plant that lives for more than 2 growing seasons.
Petiole-a leaf
stalk.
Pinnate-with 2
rows of leaflets, like a feather.
Plume-a hair-like
or feather-like structure, often on a seed.
Pubescence-the
hairs on a leaf, stem or flower.
Rhizome-a
creeping, underground stem.
Rosette-a
circular, normally basal, clump of leaves.
Sheath-the
extension of leaf tissue surrounding a stem.
Simple leaf-one
with a blade in one piece; not compound.
Spike-a narrow,
non-spreading inflorescence.
Spikelet-a
single or group of floral structures in a grass.
Spur-a hollow
appendage on a flower.
Stolon-a creeping
stem along the surface of the ground.
Succulent-fleshy
and juicy.
Taproot-a thick,
central root with minimal branching.
Trifoliate leaf-a
leaf made of 3 leaflets; clover-like.
Whorled-3 or
more similar structured arranged as spokes on a wheel. |
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© 1999 University of Idaho:
Text and photographs for these pages from Idaho's Noxious Weeds, by
Robert H. Callihan and Timothy W. Miller (revised by Don W. Morishita
and Larry W. Lass).
Please contact: Ag Publishing, University of Idaho, Moscow,
Idaho 83844-2240; 208 882-7982 visit the Resources for Idaho website at
http://info.ag.uidaho.edu, for more information about this or other
publications.
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Office Information |
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120 South 400 West
Rupert, Id 83350. |
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Phone: (208)438-8195
Fax: (208)438-8195 |
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Other Information |
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