Arthraxon hispidus (Thunb.) Makino

small carp grass

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New England Distribution

Adapted from BONAP data

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North America Distribution

Adapted from BONAP data

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Facts About

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

Habitat
  • terrestrial
  • wetlands
New England state
Massachusetts
Leaf blade width
4–20 mm
Inflorescence branches
the flowers are attached to branches rather than to the main axis of the inflorescence
Glume relative length
both glumes are as long or longer than all of the florets
One or more florets
there is one floret per spikelet
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 ligule length
0.4–3.5 mm
Anther length
0.5–0.7 mm
Show All 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
    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
    Massachusetts
    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

Distribution

Connecticut
present, invasive, prohibited
Maine
absent
Massachusetts
present, invasive, prohibited
New Hampshire
absent
Rhode Island
absent
Vermont
absent

Conservation Status

Exact status definitions can vary from state to state. For details, please check with your state.

Massachusetts
not applicable (S-rank: SNA)

Native to North America?

No

Synonyms

  • Phalaris hispida Thunb.

Family

Poaceae

Genus

Arthraxon

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Information from Dichotomous Key of Flora Novae Angliae

1.  Arthraxon hispidus (Thunb.) Makino E

small carp grass. Phalaris hispida Thunb. • MA. Hydric soil of roadsides, ditches, and 
riparian forests.