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Hydrilla verticillata

(Water Thyme Hydrilla Verticillata)

Overview

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Aquatic Plant. Hydrilla verticillata is a submerged aquatic weed that crowds out native plants by shading them and outcompeting them for nutrients . Dense masses of H. verticillata interfere with recreational activities, such as boating, fishing , and swimming. H. verticillata provides a food supply for waterfowl in areas where wetland degradation has lowered their food supply, such as in Florida. Up to 30% H. verticillata cover is beneficial to most fisheries because it allows for an increase in the population of prey fish that game fish feed on.

Common Names

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Click on the language to view common names.

Common Names in English:

Florida Elodea, Florida-Elodea, Hydrilla, Indian Stargrass, Water Thyme, Water Thyme Hydrilla Verticillata, Water-Thyme, Waterthyme

Common Names in German:

Wasserquirl

Common Names in Informal Latinized N:

Hydrilla

Description

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Family Hydrocharitaceae

Herbs, annual or perennial , caulescent or without evident stem, glabrous or pubescent , entirely submersed , with both submersed and floating leaves, or with submersed stolons and emergent leaves, in fresh, brackish , or marine waters; turions rarely present. Stems rhizomatous , creeping , with abbreviated erect axis at nodes, or erect, leafy, elongate . Leaves basal, alternate, opposite, or whorled , sessile or petiolate ; stipules sometimes present, forming tubular sheath around stem; blade margins entire or serrate; veins 1--many. Inflorescences axillary , terminal , or scapose , 1-flowered or cymose , subtended by spathe ; spathe a 2-fid bract or pair of opposite bracts. Flowers unisexual , staminate and pistillate on same plants or on different plants, often with rudiments of opposite type, or bisexual , actinomorphic , rarely slightly zygomorphic; perianth epigynous , free , mostly 6-parted, then differentiated into sepals and petals, rarely 3-parted, then petals absent in Thalassia and Halophila; stamens (0--) 2--many in 1 or more whorls (inner often staminodial), epigynous, distinct or ± connate ; pollen spheric, in monads or tetrads or in slender chains; ovary 0--1, if present, inferior, 2--6[--16]-carpellate, 1-locular or falsely 6--9-locular; placentation parietal . Fruits berrylike. Seeds many, fusiform , ellipsoid , ovoid , or spheric; seed coat glabrous, papillose , or echinate .

Genera 17, species ca. 76 (10 genera, 14 species in the flora ) : nearly worldwide.

Hydrocharitaceae, like other members of the Alismatidae, have one or more (fewer than 20) scales (intravaginal squamules ) in the axils of their leaves. These scales (or hairs in some taxa) secrete mucilage and are without any venation . The structures are often referred to as "squamulae intravaginales" or "intravaginal scales" in the literature.[1]

Genus Hydrilla

Plants perennial , of fresh or brackish waters. Rhizomes present, stolons absent. Erect stems rooted in substrate, branched or unbranched, elongate . Leaves cauline, whorled , 3--8 per node, submersed , sessile; blade linear , rarely slightly elliptic , base tapering to stem, apex acute; midvein without lacunae along side(s), blade uniform in color throughout; abaxial surface ly with prickles along midvein, without aerenchyma ; intravaginal squamules fringed with orange-brown hairs . Inflorescences 1-flowered, sessile to subsessile ; spathe not winged . Flowers unisexual , staminate and pistillate on different plants or on same plants, submersed, sessile; petals whitish to reddish. Staminate flowers : filaments distinct , released under water, rising to surface; anthers oval ; pollen in monads ;. pPistillate flowers: ovary 1-locular; floral tube long, styles 1, not 2-fid. Fruits linear, cylindric , smooth or with simple spiny processes, indehiscent. Seeds cylindric, glabrous .

Species 1: introduced , North America; Central America, South America, Eurasia , Africa, Australia.[2]

Physical Description

Species Hydrilla verticillata

Rhizomes and erect stems with turions; subterranean turions cream-brown, appearing as tubers, surface smooth ; turions from erect stems olive-green, covered with short, stiff scales . Leaves 8--15(--20) ´ 1.2--4 mm, margins serrulate . Inflorescences: spathe of 2 connate bracts. Flowers 1 per spathe; staminate pedicels 0.5 mm; pistillate flowers with floral tube 10--50 mm; ovary 1-locular. 2n = 32. Flowering summer--fall. [source]

Hydrilla verticillata apparently entered the United States in 1959 at Miami, Florida (D. F.F. Austin 1978). It was introduced as an aquarium plant, star-vine or oxygen plant (D. P. Tarver et al. 1978). By 1960 the species was reported as naturalized in Florida (G. E. Allen 1976). [source]

Hydrilla verticillata is widely distributed in the Eastern Hemisphere but it is uncertain as to where it is truly native . It grows in a variety of aquatic habitats ranging from acidic to basic, oligotrophic to eutrophic , fresh to brackish , and from a few centimeters to a meter or more if light penetrates that deeply. Growth and spread often are rapid. Stem fragments become rooted by fine, unbranched adventitious roots and soon produce vegetative reproductive structures from both subterranean and erect stems. Tubers produced on subterranean stems are pale brown; those produced on erect stems are dark olive-green and covered with short, stiff scales. Both types germinate quickly to produce new stems. [source]

Habit: Evergreen .

Flowers: Flower Color: inconspicuous, none

Size/Age/Growth

Size: 18-24" tall.

Habitat

Lakes , streams , rivers , bayous ; introduced ; 0--200 m ; introduced [3].

H. verticillata is found in freshwater but can tolerate salinities of up to 7% salinity of seawater. It has been found in springs , lakes, marshes, ditches, rivers, and tidal zones . It can grow in relatively low light and CO2 conditions. H. verticillata prefers temperatures between 20 and 27 degrees Celsius.

Typically found at an altitude of 0 to 1,609 meters (0 to 5,279 feet).[4]

Biome: estuaries, lakes , water courses , wetlands

Ecology: H. verticillata competes with native plants by growing to the water surface and forming dense mats that totally exclude sunlight from other plants, which in turn can significantly reduce aquatic plant and animal biodiversity . Large populations of H. verticillata may affect fish size and population levels where predatory fish cannot hunt effectively within the thick mats. The dense mats also affect recreational activities. Apart from interfering with fishing , boat motors can become tangled with them and swimming areas choked. H. verticillata often slows or clogs rivers , irrigation ditches, and flood control canals, creating stagnant water that is prime mosquito breeding habitat . Dense stands can even cause flooding, alter water quality by decreasing oxygen levels and increasing pH and water temperature .

Biology

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Reproduction

H. verticillata reproduces mostly by asexual vegetative fragmentation (from stem fragments), but it also grows new plants from tubers and underground tubers and reproduces sexually with flowers. One H. verticillata tuber can lead to the production of 5,000 new tubers per square m. It spreads faster in flowing water habitats because the fragments are more efficiently dispersed.

Tubers and turions can survive ice cover , drying, ingestion , and regurgitation by waterfowl. Tubers may remain viable in the sediment for several years.

Growth

Culture: Space 4-6' apart.

Soil: Minimum pH: 5.6 • Maximum pH: 6.5

Sunlight: Sun Exposure: Full Sun .

Temperature: Cold Hardiness: 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11. (map)

Taxonomy

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Unambiguous Synonyms

  1. Elodea Verticillata
  2. Elodea verticillata (L. F.) F. Muell.
  3. Serpicula verticillata L. F.
  4. Udora verticillata (L. F.) Spreng.
  5. Vallisneria verticillata (L. F.) Roxb.

Notes

Name Status: Accepted Name . Latest taxonomic scrutiny: 15-Mar-2000

Name verified on

Place of publication : Ill. bot. Himal. Mts . 1(10):376. 1839

Name verified on 23-Dec-1994 by ARS Systematic Botanists. Last updated: 22-Dec-2000

Similar Species

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Members of the genus Hydrilla

ZipcodeZoo has pages for 16 species, subspecies, varieties, forms, and cultivars in this genus:

H. alternifolia · H. angustifolia · H. dentata · H. dregeana · H. japonica · H. lithuanica · H. muscoides · H. najadifolia · H. ovalifolia · H. polysperma · H. roxburghii · H. subulata · H. verticillata (Water Thyme Hydrilla Verticillata) · H. verticillata var. crispa · H. verticillata var. roxburghii · H. wightii

More Info

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Further Reading

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Notes

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Contributors

Data Sources

Accessed through GBIF Data Portal November 21, 2007:

Identifiers

Footnotes

  1. Robert R. Haynes "Hydrocharitaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org. [back]
  2. "Hydrilla". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org. [back]
  3. "Hydrilla verticillata". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org. [back]
  4. Mean = 147.120 meters (482.677 feet), Standard Deviation = 262.520 based on 160 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]
Last Revised: 7/1/2009