Zosteraceae Family of Seagrasses

Two Sea Grasses of the Zosteraceae Family can be found in this website:

Phylogeny: Seagrasses of the Zosteraceae Family are members of the phylum Tracheophyta. Tracheophytes, unlike Bryophytes, are vascular plants that have have tissues (phloem and xylem) that allow for the transport of water and nutrients within the plant via leaves, roots and stems. They have a cuticle (waxy layer to hold in water) and stomata (pores for gas exchange). Tracheophytes may either reproduce by seeds or spores. They are in the class Magnoliopsida, which are flowering plants that have branching leaf veins and flower parts in multiples of four or five. Other plants in this class include roses, oak trees and dandelions. This family is one of nine families in the order Alismatales. Alismatids grow in terrestrial, fresh water and marine environments. The Zosteraceae Family is fairly small, and is composed of two genera, two subgenera, and twenty-one species. Species in this family are also commonly called Eel Grasses.

Morphology: Zosteracean Seagrasses are perennial, flowering, marine plants. They are not true grasses. The leaves are long, thin and strap-like or hair-like. The leaves may be flat or ovate in cross-section. The leaves grow alternatingly from a horizontal stem (Rhizome), which anchors them to the substrate. Unlike most plants these leaves lack stomata. While some aquatic plants live at or above the surface of the water, Zosteracean Seagrasses generally spend their lives submerged.  The flowers are small, scentless, enclosed in a leaf-like bract called a spathe and arranged in a flattened spike called a spadix. The fruit is ellipsoid or crescent-shaped and contains one seed. Leaf length in this family ranges from 6 cm (2 inches) to 3 m (10 feet).

Habitat and Distribution: Zosteracean Seagrasses grow on rock, sand, or mud substrates. They live in the intertidal zone and to depths of 30 m (100 feet). Some sources state that there are deep sea species, but fail to give sufficient details to confirm a deeper depth range. Seagrasses in this family are found in temperate to tropical seas around the world. Again, some sources state that they range into arctic waters, but fail to give details. Three species from this family are found in Mexican waters.

Reproduction: Zosteracean Seagrasses are a true flowering plant and grow as perennials. Adult plants are gonochoric with male and female flowers on different adult plants.  They reproduce sexually through flowers, seeds, and pollen, just like most terrestrial plants. Pollen drifting in the water fertilizes the flowers. The seeds grow on reproductive shoots called spathes. The spathes break off and drift with the currents, establishing new colonies. The seeds need to land in a branched algae in order to germinate and get established. Seagrasses can pollinate both underwater and at the surface in sea water. They also reproduce asexually through the elongation of the rhizomes, which maintains established beds.

Ecosystem Interactions: Zosteracean Seagrasses provide food, shelter, and structure for various species of fish, crustaceans, mollusks, and other invertebrates.