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• True grasses
• Sorghum halepense

Sorghum halepense — Johnson grass

Facts

Johnson grass is native to the Mediterranean, but is introduced worldwide and has become an important weed of warm temperate regions. The USDA considers it one of the six most damaging weeds in the United States, due to its destructive effects on crop yields and the difficulty of controlling it. Johnson grass can be found in most New England states except for Maine.

Habitat

Anthropogenic (man-made or disturbed habitats), meadows and fields

Characteristics

• Flowers

  Anther length

  1.9–2.7 mm

  Anther number

  3

  Awn on glume

  the glume has no awn

  Floret lower bract texture

  the lemma is thin and flexible

  Glume relative length

  one or both glumes are as long or longer than all of the florets

  Glume shape

  the glume is flat or curved in cross-section

  Glume veins

  • 3
  • 5
  • 7 or more

  Inflorescence arrangement

  the plant has two types of spikelets with different reproductive structures

  Inflorescence axis orientation

  • the inflorescence axis is arched or curved outward
  • the inflorescence axis is straight

  Inflorescence branches

  the flowers are attached to branches rather than to the main axis of the inflorescence

  Inflorescence length

  100–500 mm

  Inflorescence type (general)

  the spikelets are borne on stalks or on branches

  Inflorescence type (specific)

  the inflorescence has pairs (or trios) of spikelets, but with one always either missing a stalk or on a shorter stalk than the other

  Lemma awn base

  the awn is attached right at the tip of the lemma

  Lemma awn length

  Up to 13 mm

  Lemma awn number

  • the lemma has no awn
  • the lemma has one awn on it

  Lemma cross-section

  the lemma is flat or rounded if you cut across the midpoint

  Lemma surface

  the surface of the lemma is relatively smooth (not counting any longitudinal veins or hairs)

  Lemma tip

  the lemma tip is split into two or more points

  Lemma vein number

  • 1
  • 3

  One or more florets

  there is one floret per spikelet

  Spikelet axis tip

  there is no extension of the spikelet axis beyond the tip of the spikelet

  Spikelet disintegration

  the spikelet breaks off below the glumes

  Spikelet length

  3.6–6.5 mm

  Spikelets spiny

  the spikelets do not appear spiny

• Growth form

  Lifespan

  the plant lives more than two years

  Rhizomes

  yes

  Roots

  the plant has rhizomes (horizontal underground stem with roots growing from it)

• Leaves

  Leaf auricles

  the leaves do not have auricles

  Leaf blade width

  8–40 mm

  Leaf ligule length

  2–6 mm

  Leaf ligule type

  the leaf ligule is in the form of a membrane with fine hairs

  Leaf sheath closed around stem

  the margins of the leaf sheath are overlapping and not fused together except in the basal half (or less)

  Leaf sheath hair type

  there are no hairs on the surface of the leaf sheath

  Leaf sheath hairs

  there are no hairs on the surface of the leaf sheath

• Place

  Habitat

  terrestrial

  New England state

  • Connecticut
  • Massachusetts
  • Vermont

  Specific habitat

  • man-made or disturbed habitats
  • meadows or fields

• Stem, shoot, branch

  Stem orientation

  the stems are upright

  Stem spacing

  the stems grow singly or a few together (they may form diffuse colonies)

Wetland status

Usually occurs in non-wetlands, but occasionally in wetlands. (Wetland indicator code: FACU)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae