Stonewort
Chara is an alga that grows in alkaline water pools. Chara and its relatives have the most complex body plan of any alga. These plants form shoots and develop leaf-like structures and are anchored into the pond bed with a simple rooting system. They can easily be mistaken for an aquatic flowering plant - with meristems, shoots, leaves, roots and many different nutrient-conducting vascular systems - that grow in water rather than on the land like most flowering plants. In fact, Chara is often confused with the pond hornwort (Ceratophyllum demersum) which, although aquatic, is a flowering plant with a complex body.
Land plants are derived from a branch of the algae called the streptophtye algae, which include Chara. It has long been known Chara had certain Characteristics that suggested it was closely related to the land plants and the most recent studies on the relationship of green plants have borne this out.
We know that Chara and its relatives are an ancient group because there are fossilized remains of the thick-walled zygote (the cell that form when an egg is fertilized by a sperm) in sediments deposited in the Silurian Period. This indicates that the forebears of modern Chara plants grew in water bodies at least 430 million years ago and likely earlier.
The morphological complexity of Chara is something that is puzzling botanists. Is Chara simply a 'missing link' between algae with simple bodies and land plants with complex organs and tissues? Or did the complex body that you see in Chara evolve independently of the evolution of complex bodies in land plants. That is, was Chara an 'independent experiment' in complexity? We do not know but researchers at Oxford University and around the world are working hard to find out.
Chara plants are also known as stoneworts - stone plants. The 'stony' part of the plant is composed calcium carbonate in the form of hard crystalline calcite that impregnates cell walls. Calcite is produced by diverse groups of organisms, from the unicellular algae to shelly invertebrates. The calcite protects these organisms from herbivores and predators. The calcite-impregnated walls of Chara make this plant less appealing to grazers. The next time you see a Chara plant, take a small piece and rub the stem between your fingers. If it is hard and gritty, it is likely to be Chara but if it is soft, you may have picked up Ceratophyllum demersum!
Further reading
Graham JE et al. 2009. Algae. Benjamin-Cummings Publishing Company.
Leliaert F et al. 2012 Phylogeny and molecular evolution of the green algae. Critical Reviews in Plant Science 31: 1-46.
Guiry MD and Guiry GM 2014. AlgaeBase. National University of Ireland, Galway.
Liam Dolan