Podostemum ceratophyllum — horn-leaved riverweed
![Plant form: Podostemum ceratophyllum. ~ By Arthur Haines. ~ Copyright © 2024 Arthur Haines. ~ arthur.d.haines[at]gmail.com](https://newfs.s3.amazonaws.com/taxon-images-1000s1000/Podostemaceae/podostemum-ceratophyllum-ha-ahaines.jpg)
![Stems: Podostemum ceratophyllum. ~ By Jennifer Garrett. ~ Copyright © 2024 Jennifer Garrett. ~ gemmiferg[at]gmail.com](https://newfs.s3.amazonaws.com/taxon-images-1000s1000/Podostemaceae/podostemum-ceratophyllum-st-jgarrett.jpg)
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Facts
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
New England distribution
Adapted from BONAP data
Native: indigenous.
Non-native: introduced (intentionally or unintentionally); has become naturalized.
County documented: documented to exist in the county by evidence (herbarium specimen, photograph). Also covers those considered historical (not seen in 20 years).
State documented: documented to exist in the state, but not documented to a county within the state. Also covers those considered historical (not seen in 20 years).
Note: when native and non-native populations both exist in a county, only native status is shown on the map.
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enlargeCharacteristics
- 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
-
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)
In New England
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), special concern (code: SC)
- Massachusetts
- rare (S-rank: S2), #NAME? (code: #NAME?)
- Rhode Island
- extremely rare (S-rank: S1), concern (code: C)
- Vermont
- extremely rare (S-rank: S1)
From Flora Novae Angliae dichotomous key
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.