Podostemum ceratophyllum Michx.

horn-leaved riverweed

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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

Horn-leaved riverweed inhabits medium- to fast-flowing rivers bottoms with ledge, cobble or sand substrates. It is the only temperate North American species in a mainly tropical family (Podostemaceae), and is rare throughout New England, appearing on state endangered species lists in all states except New Hampshire. However, it may be more common than than this indicates, as riverbeds are likely under-botanized.

Habitat

Riverine (in rivers or streams), shores of rivers or lakes

Characteristics

Habitat
aquatic
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Leaf position
the leaves are all submerged underwater
Leaf arrangement
alternate: there is one leaf per node along the stem
Petal or sepal number
there are no petals, sepals, or tepals in the flower, or they are not clearly present
Petal color
NA
Specific leaf type
  • the leaf is divided into two equal parts; these parts may also be divided into two further parts
  • the leaf is not divided, rather the blade is made up of one segment
Floating leaf shape
NA
Fruit type (general)
the fruit is dry and splits open when ripe
Show All Characteristics
  • Clonal plantlets
    Turion length
    0 mm
  • Flowers
    Carpels fused
    the carpels are fused to one another
    Flower lower lip length
    0 mm
    Flower number
    1
    Flower position
    • the flowers are above the surface of the water
    • the flowers are below the surface of the water
    Flower symmetry
    NA
    Inflorescence type
    • the flowers grow out of the axil (point where a branch or leaf is attached to the main stem)
    • the inflorescence has only one flower on it
    Inflorescence width
    Up to 2 mm
    Length of flower stalk
    Up to 10 mm
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    2
    Ovary position
    the sepals and/or petals are attached below the ovary
    Palate on corolla
    NA
    Petal and sepal arrangement
    the flower includes neither petals nor sepals
    Petal appearance
    NA
    Petal color
    NA
    Petal fringed edges
    NA
    Petal fusion
    NA
    Petal hairs on inner/upper surface
    NA
    Petal length
    0 mm
    Petal number
    0
    Petal or sepal number
    there are no petals, sepals, or tepals in the flower, or they are not clearly present
    Pistil number
    1
    Sepal appearance
    NA
    Sepal length
    0 mm
    Sepal number
    0
    Sepals fused only to sepals
    NA
    Spur length
    0 mm
    Stamen number
    1 or 2
    Stamen position relative to petals
    NA
    Stamens fused
    the stamens are fused to one another at or near their bases
    Stamens fused to petals
    the stamens are not fused to the petals or tepals
    Style length
    0.5–1 mm
    Style number
    2
  • Fruits or seeds
    Fruit length
    2.5–3 mm
    Fruit type (general)
    the fruit is dry and splits open when ripe
    Fruit type (specific)
    the fruit is a capsule (splits along two or more seams, apical teeth or pores when dry, to release two or more seeds)
  • Glands or sap
    Oil glands on nodes
    none of the nodes have oil glands
    Sap
    the sap is clear and watery
  • Growth form
    Lifespan
    the plant lives more than two years
    Root septa
    the roots do not have transverse septa
    Roots floating in water
    there are no clusters of roots floating in the water
    Turions
    there are no turions on the plant
    Underground organs
    there are only slender roots on the plant
  • Leaves
    Bract position (Sparganium)
    NA
    Bract relative length
    At least 1379 mm
    Bracts
    the flowers or their pedicels have bracts at their bases
    Floating leaf basal lobes
    NA
    Floating leaf blade width
    0 mm
    Floating leaf length
    0 mm
    Floating leaf shape
    NA
    Floating leaf tip
    NA
    Floral bract form
    the bracts are much more lobed, or much less lobed, than the foliage leaves
    Floral bract length
    2–3 mm
    Leaf arrangement
    alternate: there is one leaf per node along the stem
    Leaf position
    the leaves are all submerged underwater
    Leaf special features
    none of the mentioned special features are present
    Leaf-like branch segments
    0
    Leaf-like branch shape
    NA
    Specific leaf type
    • the leaf is divided into two equal parts; these parts may also be divided into two further parts
    • the leaf is not divided, rather the blade is made up of one segment
    Staminate bract edge (Myriophyllum)
    NA
    Stipules
    the plant has stipules
    Trap-bladder length
    0 mm
    Underwater leaf blade edges
    • the underwater leaf blades are lobed
    • the underwater leaf has smooth edges, without teeth
    Underwater leaf blade shape
    • the underwater leaf blade is capillary (very fine and hair-like)
    • the underwater leaf blade is linear (very narrow with more or less parallel sides)
    Underwater leaf stalk
    yes
    Veins in floating leaf
    0
  • Place
    Habitat
    aquatic
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • in rivers or streams
    • shores of rivers or lakes
  • Stem, shoot, branch
    Flowering stem growth form
    • the flowering stem is upright
    • the flowering stem trails along the substrate, or floats in the water

Wetland Status

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

New England Distribution and Conservation Status

Distribution

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

Conservation Status

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

Connecticut
uncommon (S-rank: S3)
Maine
rare (S-rank: S2), special concern (code: SC)
Massachusetts
rare (S-rank: S2), #NAME? (code: #NAME?)
New Hampshire
uncommon (S-rank: S3), W (code: W)
Rhode Island
extremely rare (S-rank: S1), concern (code: C)
Vermont
extremely rare (S-rank: S1)

Native to North America?

Yes and no (some introduced)

Synonyms

  • Podostemum abrotanoides Nutt.

Family

Podostemaceae

Genus

Podostemum

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Information from Dichotomous Key of Flora Novae Angliae

1.  Podostemum ceratophyllum Michx. N

horn-leaved riverweed. Podostemum abrotanoides Nutt. • CT, MA, ME, NH, RI, VT. Rivers with medium to fast current, frequently on submersed ledge, but also found underwater on 
cobble, gravel, and sand substrate. More frequent than realized, some populations extending ± continuously for a km or more.