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Ruppia Balls & Algae Balls
© W.P. Armstrong 20 June 2011

One of the strangest phenomena of the plant world are filamentous plants tightly interwoven into balls in oceans and lakes. Colonies of filamentous algae also form balls of varying sizes at the bottoms of lakes.

Marimo: The Famous Algae Balls (Cladophora Balls) of Japan

The Japanese word "marimo" literally means "ball algae." Like the English noun "deer" it can be used as singular or plural. The fuzzy green balls are formed by many tangled filaments of a free-floating green alga (Cladophora aegagropila) that grow in a radial pattern (from the center outward). The original type specimen was named Aegagropila linnaei by Kützing in 1843 and this scientific name is once again the preferred correct binomial based on extensive DNA studies and the presence of chitin in the cell walls. Marimo are sometimes sold in aquarium shops as "Japanese moss balls" although they are not related to mosses. The most famous habitat for these strange balls is Lake Akan in northern Japan. They are also known from Iceland, Scotland and Estonia on the eastern shores of the Baltic Sea. Marimo are considered a national treasure of Japan. In fact, Lake Akan has been made into a National Park and there is even an annual three day Marimo Festival in which the indigenous Ainu people of Hokkaido celebrate this remarkable natural wonder. They were studied extensively by Japanese biologists, including Emperor Hirohito, and are even depicted on two Japanese postage stamps. Marimo is sold as a souvenir in Japan and is said to bring its owner good luck.

Souvenir jar of living marimo from Japan and commemorative postage stamp.

Several Marimo submersed in water. They can readily be divided into new colonies.

In Lake Akan the algae balls may be up to 20-30 cm (8-12 inches). Their growth rate is about 5 mm per year and a colony may live for many decades. The spherical shape of the marimo is maintained by gentle wave action that occasionally turns it. This also insures that all surface areas receive vital sunlight, The balls rest on the lake bottom but rise to the surface during the day as oxygen gas is produced by photosynthesis. When the oxygen escapes into the atmosphere the balls sink to the bottom. Under high magnification with a compound microscope the branched filaments of chloroplast-bearing cells can be clearly seen.

Magnified view of the filaments of Aegagropila linnaei (Cladophora aegagropila). 400x.

Marimokkori is a popularized character in Hokkaido with a green spheroid head and other globose body parts superficially resembling marimo. Marimokkori is fashioned into all sorts of dolls and other souvenirs sold in Hokkaido and throughout Japan. The name is a pun derived from "marimo" (ball algae) and "mokkori" (Japanese slang term for an erection). There are many websites and YouTube videos featuring these dolls; however, Marimokkori is somewhat beyond the scope of this article.


California's Unusual Lake Balls (Ruppia maritima & R. cirrhosa)

Southern Owens Lake with floating masses of the aquatic angiosperm Ruppia cirrhosa (white arrow).

Ditchgrass (Ruppia maritima and R. cirrhosa) are two species of aquatic flowering plants that form dense floating masses in lakes, marshes and ponds throughout the state. Ruppia maritima is more common in coastal saltwater marshes and estuaries. Both species are very similar in appearance, with threadlike stems and leaves. Flowers and fruits are produced on a slender stalk (peduncle) that develops from the leaf sheath axils.

Ruppia cirrhosa with threadlike stem and leaves, and a coiled stalk (peduncle) bearing five seed-bearing fruits .

Ruppia is one of the few plants known to form "sea balls" or "lake balls," one of the strangest phenomena of the plant world. Wave action rolls thousands of floating, filamentous plants into tightly interwoven balls that vary in size and shape from a baseball to a small watermelon. Ruppia balls were abundant in the summer and fall of 1947 along the shores of Little Borax Lake in northern California. Similar fibrous balls of the marine seagrass Posidonia oceanica have been reported along shores of the Mediterranean Sea. They were mentioned in the writings of Aristotle and Theophrastus and were used by the Greeks to caulk ships and by Venetians as packing material around glassware.

A strange Ruppia ball that washed ashore on Little Borax Lake in northern California.

Armstrong, Wayne P. and Robert F. Thorne. 1989. "California Seagrasses." Fremontia 16 (4): 15-21.


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