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Weed Identification

poison hemlock

Family

Apiaceae

Scientific Name

Conium maculatum

Other Common Names:

poison hemlock
poison hemlock
poison hemlock
poison parsely

Habit

Biennial or perennial erect growing herb. A basal rosette of leaves forms the first year followed by a tall branched stem the second year.

Leaves

Alternate and basal, triangular leaves that are 20-40 cm long and deeply lobed (almost like segments of the leaf). Leaflets are oval to oblong and hairless, with toothed margins. Petioles and stem are often spotted with purple. Lower leaves have a sheath that surrounds the stem. They are innately a compound.

Identifying Characteristics

There are distinctive purple spots located on the stem of poison-hemlock. It has a taproot.

Flower Seed Head

Small white flowers are formed in umbrella like clusters that are around 2 inches wide. Individual flowers are around 2-4 mm wide.

Seed Fruit

Fruit is a schizocarp containing two seeds. After maturity, the two sides break apart, and each half is rounded on one side and flat on the other with pale brown wavy ribs.

Where Found

It is common on roadsides and unmanaged areas, such as fence rows. It will infest areas where it is unprotected such as the center of a pasture. It does not tolerate mowing well.

Growth Habit

upright and nonwoody

Thorns or Spines

not present

Approximate Flower Diameter

pencil

Dominant Flower Color

white

Flower Symmetry

radial symmetery

Leaf Hairs

no hairs

Leaf Shape

triangle

Leaf Arrangement

Varies: 
alternate
rosette

Leaf Margin

Varies: 
lobed
serrated

Leaf Structure

pinnate

Leaf Stalk

shorter than leaf

Stem Hairs

no hairs

Stem Cross Section

Varies: 
round or oval
square or multi-edged

Milky Sap

not present

Root Structure

taproot

Life Cycle

biennial

Ochrea

Varies: 
present
not present

Plant Type

Herb