Taxonomy of Eelgrass Zostera marina

Z. marina sketch  
Taxon
Latin name
Description
Phylum
Anthophyta
flowering plants / angiosperms
Class
Liliopsida
Monocotyledons; includes grasses, orchids, and palms
Subclass
Alismatidae
1 of 4 subclasses of monocots; contains mostly aquatic or semi-aquatic species
Superorder
Alismatiflorae = Alismatanae
Includes pond weeds and relatives; consists of 15 families, 56 genera, and aprox. 500 spp.
Order
Najadales
Contains 8 families total, 3 of which contain exclusively seagrasses (Cymodoceaceae, Posidoniaceae, and Zosteraceae). The family Hydrocharitaceae has 3 marine genera, the rest are fresh water only.
Family
Zosteraceae
Includes three genera: Zostera, Heterozostera and Phyllospadix; Greek “zoster” means “belt”; all representatives are seagrasses with ribbon-like leaves and creeping rhizomes
Genus
Zostera
Contain 2 subgenera- Zostera and Zosterella
Species
marina
see characteristics below
 

*Note: The taxonomy of seagrasses is continuously changing as the technology to compare them improves, including genetic studies.  

Characteristics of genus Zostera

  • Monoecious (male and female flowers on same plant)
  • Reproductive stems have spike-like spadices and unisexual flowers on one flattened side
  • Spadix enclosed within spathal sheath
  • Peduncle of spathe partly coalescent with the axis from which it springs
  • Fruit ovoid or ellipsoid
  • Rhizome with elongate internodes
  • Vegetative parts not heavily lignified (sclerenchymatic)
  • Leaf blades thin, translucent
  • Sheaths deciduous

Characteristics of Z. marina

  • Fiber bundles in the outermost part of cortex
  • Always two groups of roots at each node
  • Leaf sheaths are tubular and rupturing with age
  • Generative shoots are terminal; retinacula absent
Distribution of Z. marina worldwide.

Distribution

Zostera marina can be found on both coasts of the United States as well as throughout Europe and eastern Asia (see map). Although typically thought of as a cold water species, it grows as far south as the Carolinas on the U.S. east coast and the Baha Peninsula on the west coast.  This species is usually a perennial, but in Mexico, Z.. marina grows as an annual, possibly an adaptation to the heat of summer.

Origin

 Zostera is believed to have originated during the Tertiary period in the Western North Pacific Ocean (McRoy, 1968; den Hartog, 1970).  The seagrass as well as a number of other marine organisms most likely invaded the North Atlantic Ocean through the Bering Strait and the Arctic Ocean during the late Tertiary (Durham and MacNeil, 1967).

Next: Eelgrass: "A Shoot"

 

References:

den Hartog, C. 1970. The Sea Grasses of the World. North-Holland Publishing Company, Amsterdam.

Durham, J.W. and F.S. MacNeil. 1967. Cenoszoic migrations of marine invertebrates through the Bering Strait region. Pp. 326-349 in The Bering Land Bridge, D.M. Hopkins, (Editor). Stanford University Press, Stanford, CA.

Green EP and Short FT (eds) (2003) World Atlas of Seagrasses. University of California Press, Berkeley, California.

Larkum, A.W.D., Orth, R.J., Duarte. C.M. (Editors), 2006. Seagrasses: Biology, Ecology and Conservation. Springer.

McRoy, C.P. 1968. The distribution and biogeography of Zostera marina (eelgrass) in Alaska. Pac. Sci. 22:507-513.

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