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- Aquatic plants
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- Hydrilla verticillata
Hydrilla verticillata — water-thyme
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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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Facts
Water-thyme is a widespread invasive aquatic plant, native to Asia. It was introduced to North America in the aquarium trade, and first escaped in Florida in 1959. It has a wide tolerance and can grow in almost any fresh or brackish body of water.
Habitat
Lacustrine (in lakes or ponds), riverine (in rivers or streams)
Characteristics
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- Leaf position
- the leaves are all submerged underwater
- Leaf arrangement
- whorled: there are three or more leaves per node along the stem
- Leaf blade length
- 8–20 mm
- Petal or sepal number
- there are six petals, sepals, or tepals in the flower
- Petal color
-
- red
- white
- Specific leaf type
- the leaf is not divided, rather the blade is made up of one segment
- Floating leaf shape
- NA
- Underwater leaf blade width
- 1.2–4 mm
- Fruit type (general)
- the fruit is dry but does not split open when ripe
- Underwater leaf length
- 8–20 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 below the surface of the water
- the flowers are floating on the surface of the water
- Flower symmetry
- there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
- Inflorescence type
- the inflorescence has only one flower on it
- Length of flower stalk
- 0–0.5 mm
- Nectar spur
- the flower has no nectar spurs
- Number of carpels
- 3–6
- Ovary position
- the sepals and/or petals are attached above the ovary
- Palate on corolla
- no
- Petal and sepal arrangement
- the flower includes two cycles of petal- or sepal-like structures
- Petal color
-
- red
- white
- Petal fusion
- the perianth parts are separate
- Petal number
- 3
- Petal or sepal number
- there are six petals, sepals, or tepals in the flower
- Pistil number
- 1
- Sepal length
- 1.5–3 mm
- Sepal number
- 3
- Sepals fused only to sepals
- the sepals are separate from one another
- Spur length
- 0 mm
- Stamen number
- 3
- Stamens fused
- the stamens are not fused to one another
- Stamens fused to petals
- the stamens are not fused to the petals or tepals
- Style number
- 1
-
Fruits or seeds
- Fruit length
- 5–6 mm
- Fruit type (general)
- the fruit is dry but does not split 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
- the plant has turions
- Underground organs
- the plant has a rhizome (a horizontal underground stem with roots growing from it)
-
Leaves
- Bract position (Sparganium)
- NA
- 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
- Leaf arrangement
- whorled: there are three or more leaves per node along the stem
- Leaf blade length
- 8–20 mm
- Leaf blade veins
- the lateral veins are parallel or slightly arched in the direction of the tip
- Leaf blade width
- 1.2–4 mm
- 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 not divided, rather the blade is made up of one segment
- Staminate bract edge (Myriophyllum)
- NA
- Stipule appearance
- the stipules are delicate and translucent
- Stipules
- the plant has stipules
- Trap-bladder length
- 0 mm
- Underwater leaf air passage number
- At least 1439
- Underwater leaf air passage relative width
- At least 4336
- Underwater leaf air passage row number
- 0
- Underwater leaf blade edges
- the underwater leaf blade edges are toothed
- Underwater leaf blade shape
-
- the underwater leaf blade is elliptic (widest near the middle and tapering at both ends)
- the underwater leaf blade is linear (very narrow with more or less parallel sides)
- Underwater leaf blade width
- 1.2–4 mm
- Underwater leaf length
- 8–20 mm
- Underwater leaf stalk
- no
- Underwater leaf stalk length
- 0 mm
- Underwater leaf tip shape
- the tip of the underwater leaf is acute (sharply pointed)
- Veins in floating leaf
- 0
-
Place
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- Specific habitat
-
- in lakes or ponds
- in rivers or streams
-
Stem, shoot, branch
- Flowering stem growth form
- 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, invasive, prohibited
- Maine
- present, invasive, prohibited
- 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
Sometimes confused with
- Egeria densa:
- leaf blades 10-40 mm long, without pickles (vs. H. verticillata, with leaf blades mostly 8-15 mm long, with small prickles along the abaxial midvein).
- Hippuris vulgaris:
- leaves with entire margins and lacking prickles (vs. H. verticillata, with leaves with serrulate margins and prickles along the abaxial midvein).
Synonyms
- Serpicula verticillata L. f.
Family
Genus
From the dichotomous key of Flora Novae Angliae
1. Hydrilla verticillata ( L. f. ) Royle E
water-thyme. Serpicula verticillata L. f. • CT, MA, ME. Lakes and slow-moving rivers, with a broad toleratance of pH, nutrient level, and salinity. This species can vegetatively perennate by stem fragmentation and by production of tuber-like turions (these structures can be produced underwater and beneath the substrate the plant is rooted in).