Amborella: the Earth’S First Smile

Living Fossils Amborella: The Earth’s First Smile The flowering plant Amborella trichopoda is perhaps the most- primitive flowering plant on Earth. It is the sole member of the Family Amborellaceae. Angiosperms or flowering plants are believed to have diverged from Gymnosperms – about 130 million years ago – roughly about as long ago as Amborella trichopoda’s history began. The study of flowering plants is difficult because flowers are fragile and there are very few fossil flowers. Charles Darwin too had major problems trying to figure out the hows and whens of the evolution of flowering plants and called the appearance of flowering plants “an abominable mystery.” If only he had studied Amborella trichopoda closely. Amborella trichopoda grows naturally only in the rain forests of New Caledonia—an island in the South Pacific. It is a small shrub. Amborella plants are either male or female. The plants bear tiny bunches of greenish- yellow flowers. Interestingly, the flowers possess not petals, but petal-like organs called tepals. Male flowers have 9-11 tepals and 11-22 stamens, which carry pollen. Female flowers have 5-8 tepals, a few sterile stamens called staminodes, and four to six carpels. The fruit is a red coloured berry with a single seed. Cross-pollination between plants is required for fruit production. The evergreen leaves are alternately arranged and have slightly serrated margins. Amborella does not have vessels for conducting water. This is a primitive feature as almost all other AngiospermS show the presence of such vessels. It is now known that within the first fifteen million years of Angiosperm history, three major lineages of flowering plants— monocotyledons, eumagnoliids and eudicotyledons—were “missing link” between angiosperms and more-ancient established. This was a time of tremendous experimentation in gymnosperms such as pines, ginkos, and cycads. nature and enormous variations in floral and vegetative Despite an unbroken chain of existence that has lasted for characteristics. Amborella is probably the last remnant of one of 130 years, the risk that Amborella runs is that of extinction. Its the most ancient lineages of Angiosperms. Genetic studies show geographical range is severely restricted and the challenges of that it is either at or at least, very near the base of the flowering environmental degradation and pollution cannot be ignored. plants. Simply put, Amborella represents a line of flowering plants However, a small gene bank of Amborella is also maintained in that diverged very early from all the other species of flowering USA. plants still alive. It is the closest we have got to a living ancestral In 1975, Virginia and Todd Keeler-Wolf, students at the flowering plant. University of California, Santa Cruz (UCSC) USA, shipped back Flowering plants are distinguished from all other plants by some samples of Amborella under the guidance of Ray Collett the differences in reproductive biology. A study published in Nature (Founder Director UCSC). The Arboretum at UCSC still supplies (2006) by a team led by Prof. William E. Friedman, University of scientists with botanical samples they need for studies on Colorado, USA, focused on a novel type of embryo sac that is Amborella. The Amborella genome is being sequenced. More seen in Amborella. Apparently, Amborella has one extra sterile information is available at: http://www.amborella.org/. cell that accompanies typical egg cells in the embryo sac—a Henry David Thoreau said that the Earth laughs with flowers; discovery that harks back to Amborella’s non-flowering ancestors. if so, Amborella was the Earth’s first smile. The discovery of the unique configuration of the egg apparatus has been compared to being, “… akin to finding a fossil amphibian Dr Sukanya Datta with an extra leg.” At the very least Prof. Friedman’s discovery Scientist NISCAIR posted to Director General's Technical Cell, CSIR HQ suggests that the reproductive structure of the plant may be the Email: [email protected] SCIENCE REPORTER, December 2010 55.

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