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• Carex acutiformis

Carex acutiformis — lesser pond sedge

Facts

Lesser pond sedge is an occasional introduction from Eurasia that can form large colonies. This species was studied to determine the consequences of having flowering stems that are triangular in cross-section, versus the much stronger round, hollow stems of grasses. Triangular stems turn out to be better at twisting when they bend in the wind, so that male parts of the flowering stem are always held downwind from female parts, minimizing self-pollination.

Habitat

Marshes, meadows and fields, shores of rivers or lakes, wetland margins (edges of wetlands)

Characteristics

• Flowers

  Bumps on fruit

  there are no papillae on the perigynium surface

  Inflorescence length

  150–350 mm

  Length of scale

  • the scale is nearly as long as, or longer than, the perigynium
  • the scale is shorter than the perigynium

  Lowest spike length

  30–80 mm

  Lowest spike stalk length

  At least 0 mm

  Lowest spike width

  Up to 7 mm

  Perigynium beak

  the perigynium has a beak

  Perigynium beak length

  0.3–0.6 mm

  Perigynium beak orientation

  the beak of the perigynium is straight, and in line with the perigynium

  Perigynium beak serrations

  the perigynium beak has no serrations

  Perigynium beak teeth

  • the perigynium beak is divided at the top into two teeth
  • the perigynium beak is not divided at the tip into two teeth, or the teeth are very tiny

  Perigynium beak teeth length

  Up to 0.2 mm

  Perigynium color

  glaucous (with a whitish bloom)

  Perigynium cross-section

  • the perigynium is relatively flat in cross-section
  • the perigynium is trigonous (triangular) in cross-section

  Perigynium hairs

  the perigynium has no hairs

  Perigynium length

  3–4.5 mm

  Perigynium nerve number

  12–18

  Perigynium nerve texture

  the nerves on the perigynium are raised, even after drying the perigynium

  Perigynium nerves lower side

  6–9

  Perigynium nerves upper side

  6–9

  Perigynium orientation

  the perigynia are oriented vertically or pressed against the axis or adjacent perigynia

  Perigynium puffy

  the achene is tightly enclosed by the perigynium

  Perigynium shape

  the perigynium body is ovate (egg-shaped)

  Perigynium width

  1.4–2.1 mm

  Perigynium winged

  the perigynium has no wings

  Pollen- and seed-producing spikes

  some of the spikes produce perigynia

  Pollen-producing spike number

  1–3

  Scale awn

  the carpellate scale has an awn on it

  Scale awn texture

  the carpellate scale awn has tiny teeth

  Scale color

  • brown
  • purple to black

  Scale tip

  • the carpellate scale tip is acuminate (tapered to a narrow point)
  • the carpellate scale tip is acute (has a sharp point)

  Spike on stalk

  • the lowest spike on the plant has a peduncle
  • the lowest spike on the plant is not borne on a peduncle

  Spike orientation

  the spikes are oriented vertically or pressed against the axis

  Spikes per stem

  2-15

  Stigma branching

  the stigmas have three branches

  Top spike

  the uppermost spike contains only staminate flowers

• Fruits or seeds

  Achene dimples

  the achene has no folds or dimples

  Style persistence

  the style stays on the mature achenes

• Growth form

  Rhizomes

  there are long rhizomes present

• Leaves

  Leaf arrangement

  the leaves are all produced from the base of the plant

  Leaf blade cross-section

  the leaf blade is flat or M-shaped, with two prominent side-veins

  Leaf blade texture

  the leaf blade is smooth and hairless, or rough and sandpapery

  Leaf bumps

  the upper surface of the leaf blade does not have papillae

  Leaf sheath bumps

  there are no papillae at the top edge of the leaf sheath

  Leaf sheath color

  • the leaf sheath has no pink, red or purple tinting
  • the leaf sheath is tinted pink, red or purple

  Leaf sheath dots

  there are red dots on the translucent tissues of the leaf sheathes

  Leaf sheath folds

  there are no corrugations on the leaf sheath

  Leaf sheath texture

  the leaf sheath feels smooth, and has no hairs

  Ligule length

  5–14 mm

  Lowest bract sheath

  the lowest bract has no sheath (or a very short sheath up to four millimeters in length)

  Lowest leaf blade width

  5–8 mm

  Lowest leaf sheath texture

  the leaf sheath feels smooth (it may have soft hairs)

  stem leaf blade width

  5–8 mm

• Place

  Habitat

  wetlands

  New England state

  • Connecticut
  • Massachusetts

  Specific habitat

  • edges of wetlands
  • marshes
  • meadows or fields
  • shores of rivers or lakes

• Stem, shoot, branch

  Plant height

  15–130 cm

  Relative stem height

  • the main stem is equal to or shorter than the leaves
  • the main stem is taller than the leaves

  Stem cross-section

  the main stem is roughly triangular in cross-section

  Stem spacing

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

Wetland status

Occurs only in wetlands. (Wetland indicator code: OBL)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae