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Amaranthus tuberculatus — rough-fruited water-hemp

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Facts

Rough-fruited water-hemp is introduced in Europe and other continents, and in much of North America, including New England. However, a few populations in Vermont appear to be native. This species is considered a noxious weed of crops in parts of the Midwest, where it has been documented to evolve resistance to multiple pesticides.

Habitat

Anthropogenic (man-made or disturbed habitats), marshes, wetland margins (edges of wetlands)

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
  • terrestrial
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Vermont
Flower petal color
NA
Leaf type
the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
Leaf arrangement
alternate: there is one leaf per node along the stem
Leaf blade edges
the edge of the leaf blade is entire (has no teeth or lobes)
Flower symmetry
  • NA
  • there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
  • there is only one way to evenly divide the flower (the flower is bilaterally symmetrical)
Number of sepals, petals or tepals
  • there are five petals, sepals, or tepals in the flower
  • there are four petals, sepals, or tepals in the flower
  • there are three petals, sepals, or tepals in the flower
Fusion of sepals and petals
both the petals and sepals are separate and not fused
Stamen number
  • 0
  • 5
Fruit type (general)
the fruit is dry but does not split open when ripe
Fruit length
1.5–2 mm
Show all characteristics

  • Clonal plantlets

    Bulbils
    the plant does not appear to have bulbils
    Bulblets replace flowers
    there are no bulblets where the flowers are located

  • Flowers

    Anther opening
    the anthers have narrow slits or furrows that run lengthwise along the anthers
    Anther spurs
    the anthers do not have spurs on them
    Calyx symmetry
    there are two or more ways to evenly divide the calyx (the calyx is radially symmetrical)
    Carpels fused
    the carpels are fused to one another
    Cleistogamous flowers
    there are no cleistogamous flowers on the plan
    Corolla morphology
    NA
    Corolla palate
    NA
    Corona lobe length
    0 mm
    Epicalyx
    the flower does not have an epicalyx
    Epicalyx number of parts
    0
    Filament surface
    the filament is smooth, with no hairs or scales
    Flower description
    the flower has a superior ovary, and lacks a hypanthium
    Flower petal color
    NA
    Flower symmetry
    • NA
    • there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
    • there is only one way to evenly divide the flower (the flower is bilaterally symmetrical)
    Flowers sunken into stem
    no
    Form of style
    • NA
    • the style is unbranched, but it has two or more narrow appendages that are part of the stigma
    Fusion of sepals and petals
    both the petals and sepals are separate and not fused
    Horns in hoods (Asclepias)
    NA
    Hypanthium
    the flower does not have a hypanthium
    Inflorescence one-sided
    the flowers are arrayed in a spiral around the inflorescence axis or branches, or occur singly, or in several ranks
    Inner tepals (Rumex)
    NA
    Nectar spur
    the flower has no nectar spurs
    Number of pistils
    • 0
    • 1
    Number of sepals, petals or tepals
    • there are five petals, sepals, or tepals in the flower
    • there are four petals, sepals, or tepals in the flower
    • there are three petals, sepals, or tepals in the flower
    Number of styles
    3
    Ovary position
    the ovary is above the point of petal and/or sepal attachment
    Petal and sepal arrangement
    • the flower includes neither petals nor sepals
    • the flower includes only one cycle of petals or sepals
    Petal and sepal colors
    green to brown
    Petal appearance
    NA
    Petal folds or pleats
    NA
    Petal hairs (Viola)
    NA
    Petal number
    0
    Petal tip shape
    NA
    Petal tips (Cuscuta)
    NA
    Reproductive system
    all the flowers on each plant have only carpels or only stamens, with only one type being present on each plant (dioecious)
    Scales inside corolla
    NA
    Sepal and petal color
    NA
    Sepal appendages
    the sepals do not have appendages on them
    Sepal appendages (Oenothera)
    NA
    Sepal number
    0–5
    Stamen attachment
    • NA
    • NA
    • the stamens are not attached to the petals or tepals
    • the stamens are not attached to the petals or tepals
    Stamen number
    • 0
    • 5
    Stamen position relative to petals
    • NA
    • the stamens are lined up with the sepals
    Staminodes
    there are no staminodes on the flower
    Umbel flower reproductive parts
    NA
    Upper lip of bilabiate corolla
    NA

  • Fruits or seeds

    Achene relative orientation
    the achenes are perpendicular to the plane of the perianth (vertical)
    Achene shape
    • the achenes are another shape in outline
    • the achenes are circular in outline
    • the achenes are oval in outline
    Achene surface (Polygonum)
    NA
    Achene type
    the fruit is a utricle (a type of achene in which the pericarp is loosely attached and often readily removed)
    Berry color
    NA
    Capsule color (Viola)
    NA
    Capsule ribs
    NA
    Capsule splitting
    NA
    Fruit (pyxis) dehiscence
    • NA
    • the pyxis bursts open or shatters without a clear seam
    Fruit features (Brassicaceae)
    NA
    Fruit length
    1.5–2 mm
    Fruit locules
    one
    Fruit shape
    • the fruit is obovoid (egg-shaped, but with the widest point above the middle)
    • the fruit is spherical
    Fruit type (general)
    the fruit is dry but does not split open when ripe
    Fruit type (specific)
    • the fruit is a pyxis (when dry it splits around the middle, and the top falls off, exposing the seeds)
    • the fruit is an achene (dry, usually one-seeded, does not separate or split open at maturity)
    Legumes (Fabaceae)
    NA
    Mericarp length
    0 mm
    Mericarp segment shape (Desmodium)
    NA
    Other markings on berry
    NA
    Ovary stipe
    the ovary or fruit does not have a stipe
    Placenta arrangement
    the plant has basal placentation, where one or a few ovules develop at the base of a simple or compound ovary
    Rows of seeds in fruit (Brassicaceae)
    NA
    Schizocarpic fruit compression
    NA
    Schizocarpic fruit segments
    0
    Septum in fruit (Brassicaceae)
    NA
    Wings on fruit
    the fruit does not have wings on it
    prickles on fruits
    the fruits do not have thorn-like defensive structures

  • Glands or sap

    Glands on leaf blade
    the leaf blades do not have glandular dots or scales
    Sap
    the sap is clear and watery
    Sap color
    the sap is clear

  • Growth form

    Horizontal rooting stem
    the plant does not have stolons
    Lifespan
    the plant lives only a single year or less
    Parasitism
    the plant is not parasitic
    Plant color
    the leaves or young stems of the plant are green
    Plants darken when dry
    no
    Spines on plant
    the plant has no spines

  • Leaves

    Bracteole number (Apiaceae)
    0
    Bracts in plantain (Plantago)
    NA
    Final leaf segment length (compound lvs only)
    0 mm
    Final leaf segment length to width ratio (compound lvs only)
    0
    Final leaf segment width (compound lvs only)
    0 mm
    Hairs on underside of leaf
    the underside of the leaf is not hairy, or it has very few hairs
    Leaf arrangement
    alternate: there is one leaf per node along the stem
    Leaf blade base
    the leaf has a distinct leaf stalk (petiole)
    Leaf blade base shape
    the base of the leaf blade is cuneate (wedge-shaped, tapers to the base with relatively straight, converging edges), or narrow
    Leaf blade edges
    the edge of the leaf blade is entire (has no teeth or lobes)
    Leaf blade length
    15–150 mm
    Leaf blade shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is oblong (rectangular but with rounded ends)
    • the leaf blade is obovate (egg-shaped, but with the widest point above the middle of the leaf blade)
    • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    Leaf blade surface colors
    the upper side of the leaf blade is relatively uniform in color
    Leaf duration
    the leaves drop off in winter (or they whither but persist on the plant)
    Leaf form
    the leaves are green, with an expanded blade and a leaf-like texture
    Leaf spines
    there are no spines on the leaf edges
    Leaf stalk attachment to leaf
    the petiole attaches at the basal margin of the leaf blade
    Leaf stalk base
    the petiole base clasps the stem or sheathes the stem
    Leaf type
    the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Leaf types
    There is a gradual change in appearance of the leaves from the base (or near the base) of the plant to those from further up on the stem, with leaves progressively changing as one moves higher on the stem (often becoming shorter, or less toothed/lobed, and/or with shorter petioles).
    Leaflet number
    0
    Leaflet petiolules
    NA
    Leaves per node
    there is one leaf per node along the stem
    Pinnately compound leaf type
    NA
    Specific leaf type
    the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Stipels
    NA
    Stipule features
    NA
    Stipules
    there are no stipules on the plant

  • Place

    Habitat
    • terrestrial
    • wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Vermont
    Specific habitat
    • edges of wetlands
    • man-made or disturbed habitats
    • marshes

  • Stem, shoot, branch

    Branched tendrils
    NA
    Flowering stem cross-section
    the flowering stem is circular, or with lots of small angles so that it is roughly circular
    Hooked hairs on stem between nodes
    no
    Leaves on stem
    there is at least one full leaf above the base of the flowering stem
    Plant height
    50–300 cm
    Stem roughness between nodes
    the stem does not feel rough
    Tendril origin
    NA
    Tendrils
    the plant does not have tendrils

Wetland status

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

In New England

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
Rhode Island
absent
Vermont
present

Conservation status

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

Massachusetts
not applicable (S-rank: SNA)
Vermont
rare (S-rank: S2)

From Flora Novae Angliae dichotomous key

17.  Amaranthus tuberculatus (Moq.) Sauer N│EC

rough-fruited water-hemp. Acnida altissima (Riddell) Moq. ex Standl.; A. tamariscina (Nutt.) Wood var. prostrata Uline & Bray; A. tuberculata Moq.; Amaranthus altissimus Riddell; 
A. ambigens Standl.; A. rudis Sauer; A. tuberculatus (Moq.) Sauer var. prostratus (Uline & Bray) Seymour; A. tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea & Tardif; A. tuberculatus (Moq.) Sauer var. subnudus S. Wats. • CT, MA, ME, NH, VT. Fresh water wetlands and shores, gardens, dumps, and open rights-of-way. Introduced to much of New England but some populations appearing native in VT (and these of conservation concern). Two species within this complex have frequently been recognized— Amaranthus tuberculatus and A. rudis. The former is eastern and characterized by carpellate flowers with 1 or 2 sepals and indehiscent fruits, while the latter is western and characterized by carpellate flowers that lack sepals (or have vestigial ones) and dehiscent fruits (among other characters). Midwestern populations have long been known to problematic (they intergrade) and have been considered to be hybrids. However, Pratt and Clark (2001) showed that a geographic cline (east to west) exists for the morphology (i.e., the phenotypic expression cannot be described simply as two species with hybridization where they overlap). Costea and Tardif (2003a) proposed a solution that treats these two species as varieties. However, changing the rank does not alter the fact that two forms cannot be confidently identified over a significant proportion of their range. Therefore, A. tuberculatus is treated here as a single, variable entity (as suggested by Pratt and Clark).

Native to North America?

Yes and no (some introduced)

Sometimes confused with

Amaranthus cannabinus:
fruit mostly 2.2--3.5 mm long and leaf blades linear to lanceolate (vs. A. tuberculatus, with fruit 1.5--2 mm long and leaf blades lanceolate to ovate).
Amaranthus palmerii:
carpellate flowers with 5 sepals 2--4 mm long (vs. A. tuberculatus, with carpellate flowers lacking sepals or with 1 or 2 vestigial ones shorter than 1 mm).

Synonyms

  • Acnida altissima (Riddell) Moq. ex Standl.
  • Acnida tamariscina (Nutt.) Wood var. prostrata Uline & Bray
  • Acnida tuberculata Moq.
  • Amaranthus altissimus Riddell
  • Amaranthus ambigens Standl.
  • Amaranthus rudis Sauer
  • Amaranthus tuberculatus (Moq.) Sauer var. prostratus (Uline & Bray) Seymour
  • Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea & Tardif
  • Amaranthus tuberculatus (Moq.) Sauer var. subnudus S. Wats.

Family

Amaranthaceae

Genus

Amaranthus