Else Marie Friis
Various fruits and seeds of Early Cretaceous flowering plants, reconstructed from synchrotron radiation X-ray tomographic microscopy (SRXTM) scans.
Gert Hansen, SCCAP, Copenhagen
Unlike animals, who began their evolutionary journey in the water, all terrestrial plants in existence today may have been on land all along, explains a new study. While biologists agree that the evolutionary tree for plants begins with green algae, a team of Danish scientists theorize that the algae from which all plants derive had been lounging on land for hundreds of millions of years rather than floating around in the oceans before drifting inland. A plant's cell wall is an important adaptation to living on land because it provides support for the plant to withstand the force of gravity, which wouldn't have the same effect in water. "We realized that algae have a cell wall that's similarly complex to terrestrial plant cell walls, which seemed peculiar because ancient algae were supposedly growing in water," co-author Jesper Harholt of Carlsberg Laboratory said in a statement. After analyzing the genetic data of a terrestrial species of green algae, the researchers found a number of genes linked to light tolerance and drought tolerance -- not exactly concerns of an aquatic organism -- that are shared with terrestrial plants. The findings of this study,published in Trends in Plant Science
, reimagine a major milestone in the evolutionary trajectory of plant life. Although we tend to focus on animal evolution, specifically our own ancestral lineage, the plant kingdom has a rich natural history all its own.Fleeting Flowers and Late Bloomers: Photos
All plants, both aquatic and terrestrial, have a single common ancestor,according to a 2012 analysis by an international team of researchers
. The first photosynthetic bacteria arose on Earth an estimated 3.4 billion years ago, while plant life first entered the picture between between 1 billion and 1.5 billion years ago. The study, published in the journal Science, lends weight to the idea that a single ancestor paved the way for the plant kingdom after a plastid -- a class of organelles that includes chloroplasts, which contain chlorophyll -- joined with a cyanobacterium in a symbiotic union. The researchers found that plastids present in all green plants and glaucophytes, a group of freshwater algae (seen here), contain hints of evolution from the earliest cyanobacteria in its DNA.Photos Capture Some of the Oldest Trees on Earth
The earliest known terrestrial plant ancestors date back some 500 million years. Prior to that, all life in the plant kingdom was aquatic. The closest living relatives to land plants are Zygnematales, microscopic algae that used conjugation, a method of sexual reproduction,according to a study published in BMC Evolutionary Biology in 2011
. This reproductive strategy differs from that used by land plants today, but researchers uncovered the ancestral line through analysis of 129 genes from 40 different plant taxa.Video: 4 Ways Algae Is Awesome
U.S. Department of Agriculture
During the Silurian period, around 410 million years ago, the oldest known vascular plants, also known as tracheophytes, made their debut. A vascular system in a plant allows it to transport water and nutrients internally. This system offers a tremendous advantage over non-vascular plants. First, it allows the movement of the plant's life essentials throughout its entire body no matter how large it gets, so plants can grow bigger. Vascularity also provides a support structure for plants, meaning they can grow taller. Finally, because fluids can be contained internally, plants can also grow in drier climates.Cactus Plants Are Vanishing: Photos
, also known as a "seed fern" for its appearance, even though ferns don't produce seeds, isthe earliest known species of seed plant
. Tracing back to the Devonian period some 400 million years ago,
produced seeds without cones, flowers or fruit as a carrier. Scientists uncovered fossil fragments and the seeds themselves for this ancient species in Randolph County, W.Va. Extinct seed ferns, known as Pteridospermatophyta, have also been found fossilized elsewhere in the United States and Australia.The Surprising Secrets of Well-Traveled Seeds: Photos
Frank Mannolini/New York State Museum
The earliest known trees didn't grow in Brooklyn, but they were natives of the Empire State somewhere between 300 million and 390 million years ago. First dug up in the late 19th century near Gilboa, N.Y., fossils for what were later called
trees were unearthed by flash flood. Because the fossils only contained the tree's trunk, no one at the time knew what they really looked like. In 2004, scientists discovered a
full fossil of this ancient tree
that revealed what the plant looked like. Hundreds of millions of years ago when they were alive,
trees stood close to 30 feet tall and looked almost like palm trees, as seen in this artist's sketch.There Are 3 Trillion Trees on the Planet
Thomas J. Lemieux, University of Colorado at Boulder
, pictured here, may not have the prettiest petals in any given flower garden, but this plant holds the distinction of being the oldest known species of petal-bearing plant still in existence today. Found in the rainforests of New Caledonia, a French territory in the South Pacific,
is a living fossil that first appeared on Earth an estimated 130 million years ago. In 2006,researchers suggested
this plant might fill the evolutionary gap between modern flowering plants and their ancestors.
wasn't the first flowering plant in Earth's history, however. In 2013, scientists announced the discovery of ancient pollen grains with features often seen in flowering plants in two core samples from northern Switzerland. The pollen grains date back to the Middle Triassic period, around the time of the earliest known dinosaurs, around 245 million years agoreported LiveScience
.Oldest Flowering Plant Genome Mapped: Photos
PNAS and University of Göttingen/Alexander Schmidt
Around 40 million years ago, some plants started developing a taste for meat. That's when the fossil record places the earliest known carnivorous plants on Earth. Along what is now the Baltic coastline,researchers from the University of Göttingen in Germany found the fossilized leaves
of a plant related to other specimens from the Roridulaceae family, which trap their prey on long, sticky hairs,New Scientist reported last year
. The fossils date between 35 million and 47 million years old. The fossils' appearance in Europe surprised botanists, given that the plant family is endemic to South Africa. Botanists once thought the timeline of carnivorous plants began with the unearthing of fossils of
, which date back some 145 million years ago to the Early Cretaceous period. Upon further examination,
researchers determined that
was misclassified.Carnivorous Plants Communicate with Bats
Beginning around 11,400 BCE, during the Epipalaeolithic era, humans began taking over for Mother Nature, when our ancient ancestors started selecting plants for certain traits, such as sweetness in fruit, resilience to drought, or simply abundance. The earliest known crops planted by humans weren't cereals, like wheat, rye or barley, but rather fig trees. Archaeologists in Israel discovered a dwelling near the ancient city of Jericho that contained mutant figs, a rare kind of tree that only reproduces through human intervention by taking a cutting and planting it,NPR reported in 2006
. Flash forward to the 20th century and humans are beginning to manipulate the genes of plants directly rather than just selecting plants based on output. In 1983, a tobacco plant resistant to an antiobitic was the first transgenic, or genetically modified, crop ever produced. A decade later, genetically modified tomatoes hit store shelves in the United States, the first commercially available GM crop.Video: Can We Grow Plants on Mars?
The world may never know if dinosaurs stopped to smell the flowers, but scientists have uncovered a few more clues about the ancient blossoms that grew alongside ankylosaurs and iguanadons. Recently, researchers discovered tiny Cretaceous flower seeds dating back 110 million to 125 million years, the oldest-known seeds of flowering plants. These puny pips offer a glimpse into the biology powering the ancient predecessors of all modern flowers.
The seeds are miniscule — the largest was no more than 0.1 inch (2.5 millimeters) in diameter — and unusually well-preserved, in such good condition that their internal cell structures were still visible. For the first time, scientists were able to detect seed embryos, the part of the seed where a new plant grows and emerges, and food storage tissues surrounding them. These structures offered a rare glimpse into how the Cretaceous seeds grew, and how they compare with plants alive today.
Else Marie Friis, lead author of the study and professor emerita at the Swedish Museum of Natural History, has analyzed some of these fossil remains of angiosperms — flowering plants — preserved in soils in Portugal and North America. She and her colleagues used a relatively new visualization technique — synchrotron radiation X-ray tomographic microscopy (SRXTM), which allowed them to explore the delicate fossils without damaging or destroying them. They imaged 250 seeds spanning 75 different species (some were also different genera), revealing the embryos and nutrient structures inside the seeds in exquisite detail. [Photos: Ancient Flowering Plant May Have Lived with Dinosaurs]
Around half of the fossil seeds they examined contained preserved cell structures within their seed coats, and about 50 seeds held partial or complete embryos. Once they had 2D images of the embryos, they used software to model the embryos’ shapes in 3D, finding that their size and shape varied between seeds. In some cases, the embryos resembled those in modern plants believed to be distant relatives of the Cretaceous angiosperms.
“These observations give us new insights into the early part of the life cycle of early angiosperms, which is important for understanding the ecology of flowering plants during the emergence and dramatic radiation through the early Cretaceous,” Friis said in a video statement.
During the Cretaceous period, angiosperms evolved and diversified rapidly. Many new insect species, which also appeared during the Cretaceous, may have played a part in how quickly flowering plants took hold and thrived in the ancient landscape.
Prior evidence from living and fossil plants has suggested that the earliest angiosperms grew close to the ground and took advantage of disrupted environments, and that they moved rapidly through growth stages. All of the seeds analyzed in the study were preserved during a dormant stage in their life cycle, the authors reported. The embryos were so tiny — less than one-fourth of a millimeter — that they would need to grow more inside the seed before they could germinate.
“Our discoveries support hypotheses based on extant plants that small embryos and seed dormancy are basic for flowering plants as a whole,” Friis said. A dormant period for seeds meant that they could “wait out” a harsh environment and postpone growth until conditions were more favorable, a survival strategy practiced by many flowering plants today.
The findings were published online Dec. 16 in the journal Nature.