Female eel grass plant, note the long and slightly coiled flower stalks.
Eel grass is a very common Connecticut River submerged aquatic; it grows in 4-6 ft of water. Long grass- like leaves (ca. 3 ft in length) grow from creeping stems rooted in the river bottom. Submerged eel grass meadows are inhabited by a variety of fish, including, of course, large, fat American eels.
Sexual reproduction in eel grass is complex and interesting, even for a plant!
Populations of eel grass consist of two genders: males and females. These genders are identical with regard to vegetative characteristics; they differ only in the nature of the flowers they form. The male plants form very small flowers (0.6 mm across, there are 25.4 mm to the inch!) in which only the stamens are functional (staminate flowers). The staminate or male flowers are found on a small inflorescence that develops from the submerged stem. A staminate inflorescence may form 2,000 staminate flowers. When the staminate flowers are mature, they are cut off (abscission) from the inflorescence and float to the river’s surface. The staminate flowers are now free-floating and are carried about the river’s surface by the vagaries of wind and current; essentially they are small boats of pollen whose task is to bump into a female flower.
While the male plants are releasing thousands of free-floating staminate flowers, the female plants have formed long flower stalks that reach the water’s surface. At the ends of these stalks single flowers are formed in which only pistils are functional (pistillate flowers). Pistillate flowers remain attached to the female plant via the long flower stalk. The flowers float on the surface, more or less at a slant, causing slight depressions in the surface of the water, a kind of dimple in the surface. Staminate flowers that happen to be floating nearby slide into this small depression or dimple in the water’s surface and make contact with the pistillate flower. Pollen is transferred to the female pistillate flower (pollination). The pollen grains germinate and ultimately sperm nuclei and eggs unite and fertilization occurs. The pistillate flower’s ovary increases in size to become a small fruit within which are 200-400 seeds, each with a young embryo (the product of fertilization).
The female plant, sensing in some way that pollination and fertilization have occurred (not magic, only biochemistry), starts to pull the fruit underwater! The flower stalk starts to coil like a bed spring, the fruit to which it is attached is slowly pulled beneath the River’s surface into the safety of its depths.
The following diagram gives an overview of sex in
After reading (and I hope following) all this, you must be wondering why eel grass has evolved such a chancy and complex sexual cycle; it could have just as easily evolved flowers that self-pollinated, i.e. had functional stamens and pistils. In fact, why does eel grass bother with sex at all? It can easily reproduce vegetatively by growing more stems.
This can all be formulated into an interesting biological question, “How is cross-pollination advantaged over vegetative propagation in eel grass?”
Answer this question and (this is the hard part) scientifically prove your answer and you are on your way to fame and glory!
One last fact: Eel grass is not a true grass (family Gramineae) but is in the family Hydrocharitaceae.
Kausik, S. B. (1939) Pollination and its influences on the
behavior of the pistillate flower in
Vallisneria spiralis. American Journal of Botany
Wylie, R. B. (1917) The pollination of Vallisneria spiralis. American Midland Naturalist 18:309- 333.