The Puzzle of the Flowering Plants' Origin Investigated

Except for sea food and fish, all you eat comes directly or indirectly (through chicken, pork and beef) from flowering plants. But how they appeared is a big puzzle for the researchers.

A new research made by a team at Paul Scherrer Institute (PSI) and published in Nature comes with new data on the issue. New 3-D non-destructive imaging techniques have been employed for the first time to investigate fossilized plant seeds, confirming earlier scientific theory, previously doubted by DNA analyses.

Flowering plants emerged about 130 million years ago, but their origin is a mystery. Gnetophytes, coned, seed-bearing plants, have been linked to flowering plants; only a few genera persist in the current flora (like joint-pine or Welwitschia), but their morphology, together with the fossil remains point that gnetophytes are close relatives of the flowering plants, and of the bennettitales, a fossil group only. These 3 groups were joined into the clade of the anthophytes. But DNA analyses pointed that gnetophytes are related to conifers.

The new PSI research supports the anthophyte hypothesis. The team analyzed 70 and 120 million years old fossilized plant seeds from Portugal and North America, carbonized, but still extremely well preserved. The researchers employed the TOMCAT beamline at the PSI Swiss Light Source (SLS) to investigate the seeds. The novel phase-contrast method (MBA) revealed images of the inner structure of the seeds without harming them. While commonly employed microtomography relies on synchrotron radiation, the phase-contrast method uses the diffraction of the X-rays.

MBA delivers clear and precise visualization of the sample, even for weak absorption contrast. And each individual measurement was done in only a few minutes instead of hours.

The MBA images of the fossil seeds revealed a lot of similar traits between gnetophytes, bennettitales and flowering plants, pointing to a close relationship. The 3 groups could have sprouted from a common ancestral group, distinct from the conifers (like firs, spruces and pines).