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• Dichotomous Key
• Poaceae
• Poaceae Group 9
• Arthraxon
• Arthraxon hispidus

Arthraxon hispidus — small carp grass

Facts

Small carp grass originates from Japan and eastern Asia. It is an annual of wet areas, and can form dense stands, especially along shorelines, that can exclude native vegetation. It is widespread and invasive in the southeastern United States, but in New England, it has only been collected in Massachusetts.

Habitat

Anthropogenic (man-made or disturbed habitats), floodplain (river or stream floodplains), forests, swamps

Characteristics

• Flowers

  Anther length

  0.5–0.7 mm

  Anther number

  2

  Bristles below spikelets

  no

  Floret lower bract texture

  the lemma is thin and flexible

  Floret number

  1

  Floret types within spikelet

  all the florets within a spikelet are similar

  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

  • 1
  • 3
  • 5
  • 7 or more

  Glumes per spikelet

  2

  Inflorescence arrangement

  the spikelets are uniform

  Inflorescence axis orientation

  the inflorescence axis is straight

  Inflorescence branches

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

  Inflorescence length

  13–70 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

  Inforescence position

  • the spikelets are mainly carried at the end of the stem
  • the spikelets are mainly found at the nodes, in the axils of leaves, along the stem

  Lemma awn coiled

  the lemma awn is straight or twisted, but not coiled one half turn

  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 vein number

  • 1
  • 3

  Lower glume length

  3–5.5 mm

  Lower glume relative length

  the lower glume is nearly as long, or as long as, the upper glume

  One or more florets

  there is one floret per spikelet

  Reproductive system

  all the flowers on the plant have both carpels and stamens (synoecious)

  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 number per node

  0

  Spikelets spiny

  the spikelets do not appear spiny

  Upper glume length

  3–5.5 mm

• Growth form

  Horizontal rooting stem

  no

  Lifespan

  the plant lives only a single year or less

  Rhizomes

  no

  Roots

  there are only slender roots on the plant

• Leaves

  Basal leaves

  the plant has few or no leaves coming from the base of the flowering stem

  Leaf auricles

  the leaves do not have auricles

  Leaf blade cross-section

  the leaf blade is more or less flat in cross-section, or slightly folded or rolled inwards

  Leaf blade hairs

  the leaf blade is hairless, but it may have tiny prickles that give it a sand-papery feel

  Leaf blade length

  1–7.5 cm

  Leaf blade width

  4–20 mm

  Leaf ligule length

  0.4–3.5 mm

  Leaf ligule type

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

  Leaf margin glands

  there are no glands along the edges of the leaf blade

  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 hairs on the surface of the leaf sheath, and some of the hairs have blisters at their bases

  Leaf sheath hairs

  there are hairs on the surface of the leaf sheath

• Place

  Habitat

  • terrestrial
  • wetlands

  New England state

  • Connecticut
  • Massachusetts
  • New Hampshire

  Specific habitat

  • forests
  • man-made or disturbed habitats
  • river or stream floodplains
  • swamps

• Stem, shoot, branch

  Hairs at nodes

  the stem nodes have hairs that stand out at a shallow angle, or they curve downwards

  Plant height

  50–200 cm

  Roots at lower stem nodes

  yes

  Stem orientation

  the stems trail at the base, but turn upwards at the tips

  Stem spacing

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

Wetland status

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

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae