Growth Habit

lateral formation

individual shoot with laterals

rhizome mat

As mentioned in the previous section, an eelgrass shoot consists of a horizontal stem or rhizome that grows on or just below the surface of the sediment, and leaves that originate from a meristem. As the shoot grows, the rhizome elongates, moving across or within the sediment, forming roots as it progresses. Root initiation is directly related to formation of leaves, and during the growing season, a new leaf is initiated approximately every 14 days. When this occurs, a new set of roots emerges from a node on the rhizome at the base of what was an old leaf.

Roots emerge from node at a downward angle alternating from the left side to the right side of the rhizome, possibly adding to the stability. A seedling will produce anywhere from 2 to 12 lateral shoots during the first growing season. Of these, usually only the original shoot will differentiate into a reproductive shoot and flower the next year. After the flower shoot releases its seeds, it dies back and the original connection between the shoots within the clone will separate, leaving individual plants that are of a single clone.

Like most other temperate plants, eelgrass begins rapid growth in the spring, with leaf elongation and rhizome branching. By mid summer, the above ground biomass has reached its peak and growth slows somewhat in response to higher water temperature. In some cases, there is a second period of growth in the fall as temperatures fall again from the extreme highs of August/September.

During winter, growth is slowed considerably and short leaves are all that are evident at most meadows. From above, eelgrass is very difficult to see during winter even in shallow water unless there is macroalgae clinging to the small shoots. Although a single clone of eelgrass can survive for many years, individual shoots do not live for more than two years.

Next: Eelgrass Life History


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