Monterey Bay Aquarium Research Institute
Marine Botany
Phyllospadix: The Surfers Living in water, especially where the waves are breaking with immense force, is not easy. Some waves are so powerful that they can crash a wooden boat and smash it to pieces, but many marine organisms are able to survive in the surf-zone. As marine angiosperms, sea grasses successfully fulfill the requirements for life at sea outlined by den Hartog (1970, p.12):
  1. They are adapted to life in a saline medium. Osmoregulation is achieved by specialized epidermal cells and the leaves have no need for stomates, as opposed to terrestrial plants, because all of the gas-exchange is accomplished through the epidermis.
  2. Seagrasses have the ability to grow when completely submerged.
  3. Surf grass have a successful anchoring system to withstand tidal currents and moderate wave action.
  4. Seagrasses are able to reproduce in an aquatic medium. This adaptation called hydrophilly, which is unique to aquatic plants, allows the surf grass to perform both surface and completely submerged pollination.
The leaves of surf grasses are especially adapted to living in a turbid aquatic medium.

As mentioned above, they have no stomates that open to the exterior so the leaves have no holes that might weaken them. The interior of the leaves is composed of specialized parenchymous tissue called aerenchyma that has regularly arranged air spaces or lacunae. These internal air spaces serve for flotation and gas exchange purposes (Arber, p.187). Furthermore, the fully aquatic angiosperms have chloroplasts in the leaf epidermis while terrestrial plants only have chloroplasts inside the leaf tissue.

The leaves are flat and supple.

The reduction of vascular bundles and the absence of lignification (woody or cork material) allows the leaves to remain erect in strong water action. The natives of the Pacific coast used to weave baskets with seagrass because it is so flexible and stiffens when dries. It also resists rotting and for this same reason it was used as stuffing material in the former U.S.S.R. (Phillips & McRoy, p.301).

The leaves are also very strong.

If you pull on a leaf of Phyllospadix, you will feel a lot of resistance. The stress force for a Phyllospadix leaf blade was measured to see how much force the blade could withstand before breaking. The expected tensile strength for macroalgae is between 0.7-10 MN/meter sq. (Denny et al, 1989) and that of Phyllospadix was calculated to be 10.2 which is highly beneficial in the turbulent zone where the plant grows.

A 1988 study by McRoy & Cooper described the anatomical adaptations that allow Phyllospadix to thrive on rocky substrates in the surf exposed zone in comparison to Zostera marina, more commonly found in sheltered areas of the coast. Phyllospadix shows significantly more root hair growth than Zostera (another closely related sea grass) which might provide extra attachment force to hold on to rocks in turbid water. The roots and rhizomes of Phyllospadix also have thicker outer epidermal walls, making it more able to withstand strong wave force. The lacunae (internal air-spaces) are reduced because the plants live in a highly oxic (oxygen-rich), well-mixed environment. As would be expected for a plant that needs to be adapted to water motion in a turbulent surf-zone, Phyllospadix shows more flexible (non-lignified hypodermal) leaf tissues than does Zostera.
Phyllospadix pages copyright Erika Marin-Spiotta 1996.
Last updated: Feb. 05, 2009