IU paleobotanist identifies what
could be the mythical 'first flower'
New
analysis represents major change in the presumed nature of the planet's
earliest angiosperms
Aug. 17, 2015
BLOOMINGTON, Ind. -- Indiana University
paleobotanist David Dilcher and colleagues in Europe have identified a 125
million- to 130 million-year-old freshwater plant as one of earliest flowering
plants on Earth.
The finding, reported today in the Proceedings of
the National Academy of Sciences, represents a major change in the presumed
form of one of the planet’s earliest flowers, known as angiosperms.
"This discovery raises significant questions
about the early evolutionary history of flowering plants, as well as the role
of these plants in the evolution of other plant and animal life," said
Dilcher, an emeritus professor in the IU Bloomington College of Arts and
Sciences' Department of Geological Sciences.
The aquatic plant, Montsechia vidalii, once grew
abundantly in freshwater lakes in what are now mountainous regions in Spain. Fossils
of the plant were first discovered more than 100 years ago in the limestone
deposits of the Iberian Range in central Spain and in the Montsec Range of the
Pyrenees, near the country’s border with France.
Also previously proposed as one of the earliest
flowers is Archaefructus sinensis, an aquatic plant found in China.
"A 'first flower' is technically a myth, like
the 'first human,'" said Dilcher, an internationally recognized expert on
angiosperm anatomy and morphology who has studied the rise and spread of
flowering plants for decades. "But based on this new analysis, we know now
that Montsechia is contemporaneous, if not more ancient, than
Archaefructus."
He also asserted that the fossils used in the
study were "poorly understood and even misinterpreted" during
previous analyses.
"The reinterpretation of these fossils
provides a fascinating new perspective on a major mystery in plant
biology," said Donald H. Les, a professor of ecology and evolutionary
biology at the University of Connecticut, who is the author of a commentary on
the discovery in the journal PNAS. "David’s work is truly an important
contribution to the continued quest to unravel the evolutionary and ecological
events that accompanied the rise of flowering plants to global
prominence."
The conclusions are based upon careful analyses of
more than 1,000 fossilized remains of Montsechia, whose stems and leaf
structures were coaxed from stone by applying hydrochloric acid on a
drop-by-drop basis. The plant's cuticles -- the protective film covering the
leaves that reveals their shape -- were also carefully bleached using a mixture
of nitric acid and potassium chlorate.
Examination of the specimens was conducted under a
stereomicroscope, light microscope and scanning electron microscope.
The age of the plant at 125 million to 130 million
years is based upon comparisons to other fossils in the same area, notably the
freshwater algae charophytes, which places Montsechia in the Barremian age of
the early Cretaceous period, making this flowering plant a contemporary of
dinosaurs such as the brachiosaurus and iguanodon.
The precise, painstaking analysis of fossilized
structures remains crucial to paleobotany, in contrast to other biological
fields, due to the current inability to know the molecular characters of
ancient plants from millions of years ago, Dilcher said.
This careful examination was particularly
important to Montsechia since most modern observers might not even recognize
the fossil as a flowering plant.
"Montsechia possesses no obvious 'flower
parts,' such as petals or nectar-producing structures for attracting insects,
and lives out its entire life cycle under water," he said. "The fruit
contains a single seed" -- the defining characteristic of an angiosperm --
"which is borne upside down."
In terms of appearance, Dilcher said, Montsechia
resembles its most modern descendent, identified in the study as Ceratophyllum.
Also known as coontails or hornworts, Ceratophyllum is a dark green aquatic
plant whose coarse, tufty leaves make it a popular decoration in modern
aquariums and koi ponds.
Next up, Dilcher and colleagues want to understand
more about the species connecting Montsechia and Ceratophyllum, as well as
delve deeper into when precisely other species of angiosperms branched off from
their ancient forefathers.
"There's still much to be discovered about
how a few early species of seed-bearing plants eventually gave rise to the
enormous, and beautiful, variety of flowers that now populate nearly every
environment on Earth," he said.
Other authors on the paper are Bernard Gomez and
Véronique Daviero-Gomez of the Université Lyon, France; Clément Coiffard of the
Leibniz Institute for Evolution and Biodiversity Science, Germany; and Carles
Martín-Closas of the Universitat de Barcelona, Spain.
Support for this research was provided by the
French National Centre for Scientific Research, the Spanish Ministry of Science
and Innovation, the German Funding Agency and the European Commission, as well
as the Indiana Geological Survey and IU Bloomington Department of Geological
Sciences.
