Hydrilla verticillata — water-thyme
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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)
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
- 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)
In New England
Distribution
- Connecticut
- present, invasive, prohibited
- Maine
- present, invasive, prohibited
- Massachusetts
- present, invasive, prohibited
- New Hampshire
- absent
- Rhode Island
- absent
- Vermont
- absent
Conservation status
None
From Flora Novae Angliae dichotomous key
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).
Native to North America?
No