Surfgrass, a flowering plant but not a true grass

Low tides expose the bright narrow strips of wet seagrass growing in Monterey Bay’s lowest intertidal zone. Phyllospadix, our local surfgrass, is that rare flowering plant that grows primarily on rocks exposed to heavy surf and wave action.

The older surfgrass blades are decorated with dainty spots of crustose coralline algae (Melobesia mediocris) and small slivers of red nori (Smithora naiadum). Newer surfgrass blades are shining examples of youth, unsullied by epiphytes that have settled on their elders.

The seagrasses are strong and flexible–well adapted to life in the ocean. They have no stomates so their leaves don’t have holes to weaken their structure. The interior of the leaves is composed of specialized tissue with regular internal air spaces that provide for flotation and gas exchange.

Phyllospadix can reproduce both asexually through rhizomes and sexually by flowering. Surfgrass plants in flower can be found year-round with peak reproduction during the summer. Separate male and female plants bear tiny, inconspicuous flowers on a linear spadix (inflorescence) which is enclosed in a spathe sheath. Amazingly, pollination in this dioecious perennial can occur in air at low tide or while plants are completely submerged. Threadlike pollen (5 microns in diameter) is released from the male flowers after a low tide. Without any apparent animal vectors, water movement disperses the gelatinous strands of pollen to female flowers.

After fertilization, the fruit matures on the female spadix and the spadix curls back to reveal the developing crescent-shaped fruit. When the mature fruit detaches from the spadix, two small, bristly “arms” allow the negatively buoyant seed to catch and hook onto an articulated coralline or another attached seaweed. Germination occurs immediately after attachment with the seedling developing adventitious roots with a dense cover of root-hairs that adhere firmly to the intertidal rock.