Science Illustrated - - CONTENTS -

Why flow­er­ing plants were an evo­lu­tion­ary in­no­va­tion ar­guably more sig­nif­i­cant to us than the death of the dinosaurs.

A mod­est flower ended up af­fect­ing life on Earth more than the huge bolide that wiped out the dinosaurs. Sci­en­tists have recre­ated the small plant, to which we owe our ex­is­tence.

A4-m-long rep­tile with rows of huge spikes down its back is eat­ing its way through the juicy, green leaves of a ginkgo­phyte. The an­i­mal is a Reg­nosaurus liv­ing in a re­gion, which will be north-west­ern Europe 140 mil­lion years later. In be­tween its legs, much smaller dinosaurs move quickly about, ben­e­fit­ting from the twigs falling from the large her­bi­vore’s jaws.

At the top of the high, con­i­cal tree, an Is­tio­dacty­lus lands, fold­ing up its learther-like wings. Its toothed beak is smoth­ered in blood from the car­cass that it had for break­fast.

None of the crea­tures no­tice that trapped be­tween ferns and ginkgo­phyte roots, a small plant slowly un­folds its top leaves to greet the morn­ing sun. The small plant will soon turn evo­lu­tion up­side down. It is Earth’s first flower, and in only 40 mil­lion years, its an­ces­tors will take over the eco-sys­tems of the world in a unique bi­o­log­i­cal rev­o­lu­tion.

Sci­en­tists have for the first time re­vealed what the an­ces­tor of al­most 90 % of modern plants looked like. And they are well on their way to find­ing out how the small flower de­feated its com­peti­tors to fi­nally pave the way for our own species: hu­mans.

Flow­ers dom­i­nate the world

The descen­dants of the world’s first flower – known as flow­er­ing plants – now ex­ist al­most any­where on Earth. So far, sci­en­tists have dis­cov­ered some 300,000 dif­fer­ent species, but an­other 100,000 are prob­a­bly hid­ing in the trop­i­cal forests of the world.

The flow­er­ing plants do not only in­clude the ones that we usu­ally think of as flow­ers, such as sun­flow­ers, tulips, roses, and dan­de­lions. Leaf-bear­ing trees, fruit bushes, cac­tuses, and car­niv­o­rous plants also form part of the group. To hu­mans, the most im­por­tant ones might be grasses, in­clud­ing rice, su­gar canes, wheat, corn, etc.

The cen­tral po­si­tion in al­most all ecosys­tems has made both palaeon­tol­o­gists and botanists explore the bi­ol­ogy and ori­gins of flow­ers, try­ing to find out what the first flower looked like, which type of plant it descends from, and why it took over Earth’s fauna, when the species that ex­isted be­fore it were ap­par­ently well-ad­justed.

A ma­jor in­ter­na­tional re­search project has just an­swered one of the ques­tions: what did the first flower look like? Sci­en­tists stud­ied the ap­pear­ances and genes of al­most 800 modern plant species, and based on the re­sults, they could fig­ure out the char­ac­ter­is­tics of their com­mon an­ces­tor. The con­clu­sion was that it was very much like modern flow­ers. All its char­ac­ter­is­tics still ex­ist in flow­ers to­day – but not one flower is ex­actly like it.

In spite of its re­sem­blance to the ma­jor­ity of modern plants, the first flower was quite unique in its time. Its new char­ac­ter­is­tics pro­vided it with an evo­lu­tion­ary ad­van­tage: they al­lowed it to co­op­er­ate with an­i­mals on an un­prece­dented scale.

In­sects as­sisted flow­ers

Flow­ers’ colour­ful pe­tals func­tion as sig­nal lamps, at­tract­ing hun­gry in­sects. In or­der to get to a flower’s high-en­ergy nec­tar, in­sects must push their way past sta­mens and stig­mas. The sta­mens con­tain pollen, the flow­ers’ male ga­metes, which stick to the in­sect body. When the in­sect flies on to an­other flower, it de­posits the pollen on the flower’s stigma – the ex­te­rior part of the plant’s fe­male sex or­gan.

This re­pro­duc­tion method was very dif­fer­ent from and much more clever than in ear­lier veg­e­ta­tion. Pre­his­toric plants only ejected their pollen or spores into the air or wa­ter, count­ing on them to land in the right place – just like their modern descen­dants such as ferns and pines do to­day. The pines im­prove their chances of hitting an­other tree’s fe­male cones by mak­ing their male cones pro­duce mil­lions of pollen grains, but the ex­ten­sive pro­duc­tion wastes huge quan­ti­ties of en­ergy.

The flow­ers’ co­op­er­a­tion with in­sects en­sures a sur­plus of en­ergy, and the suc­cess was also ben­e­fi­cial to in­sects. Ac­cord­ing to stud­ies, a few mil­lion years later, many new species of wasps, bees, ants, but­ter­flies, moths, and flies emerged, whose life cy­cles were only based on flow­er­ing plants. They de­vel­oped mouth parts that were par­tic­u­larly fit for ex­tract­ing nec­tar, eat­ing flower pe­tals, or en­ter­ing fruit. They also de­vel­oped fur-like struc­tures on their bod­ies, which ef­fi­ciently col­lected pollen.

The suc­cess of the flow­er­ing plants did not only af­fect in­sects. Stud­ies in­di­cate that the ex­plo­sive growth of flow­er­ing species takes place at the same time as a marked growth in the num­bers of rep­tiles and birds. The dinosaurs were un­doubt­edly also af­fected by the ma­jor change of the ecosys­tems, but sci­en­tists have not yet found out how the large an­i­mals re­acted to the rad­i­cal change. Their bones ap­par­ently show no signs of adap­ta­tion to the new world.

Ac­cord­ing to some stud­ies, we can thank the flow­ers for our ex­is­tence. The group of mam­mals which hu­mans and al­most all other modern mam­mals be­long to was only one of a se­ries of mam­mal groups back then. And it was not by far the most suc­cess­ful one. How­ever, the sit­u­a­tion changed, when flow­er­ing plants con­quered the world. Sci­en­tists pro­pose that the dras­tic ecosys­tem

Un­like flow­er­ing plants, conifers and other gym­nosperms do not "wrap" their seeds in high-en­ergy fruit. SHUTTERSTOCK

change put most mam­mals un­der pres­sure, but our own om­niv­o­rous an­ces­tors were suf­fi­ciently ver­sa­tile to per­form well dur­ing the chal­leng­ing pe­riod.

Gene flaw caused suc­cess

The flow­er­ing plants went from noth­ing to mak­ing up to 80 % of the world’s veg­e­ta­tion in less than 40 mil­lion years – a split sec­ond in a ma­jor ge­o­log­i­cal per­spec­tive.

Be­fore flow­ers en­tered the scene, gym­nosperms, ferns, etc., dom­i­nated Earth. Gym­nosperms now i nclude pines, cy­cado­phytes, and ginkgo­phytes, but in the era of the dinosaurs, there were also other types. Their hey­day prob­a­bly lasted some 150 mil­lion years – to­day only about 1,000 species re­main on Earth. The ma­jor­ity of them are conifers, which ex­ist in cool or moun­tain­ous re­gions. To­day, sci­en­tists are al­most certain that the first flower de­vel­oped from an ex­tinct group of gymno sperms. And they are also be­gin­ning to un­der­stand the ge­netic changes which trig­gered the de­vel­op­ment.

The ma­jor break­through came when they stud­ied the prim­i­tive Am­borella tri­chopoda

flow­er­ing plant, which now only grows on a small Pa­cific is­land 1,600 km east of Aus­tralia. The sci­en­tists se­quenced the plant’s genes, only to dis­cover that its an­ces­tors’ DNA had changed rad­i­cally about 160 mil­lion years ago. The change hap­pened at least 20 mil­lion years be­fore the time which pre­his­toric flora ex­perts es­ti­mate to be the most prob­a­ble for the evo­lu­tion of the world’s first flower – and at least 30 mil­lion years be­fore the old­est known fos­silised flow­er­ing plant.

The marked change was a genome dou­bling – a ge­netic fer­til­iza­tion mishap, by which the fer­til­ized egg cell got twice as many copies of its own genes as nor­mally. In an­i­mals, such a mishap will re­sult in the off­spring be­com­ing ster­ile or dy­ing dur­ing the em­bry­onic stage or shortly af­ter birth.

But in plants, there is a slight chance that the in­di­vid­ual sur­vives and is even able to re­pro­duce. Ac­cord­ing to the sci­en­tists, the ex­tra genes can make sure that the plant and its descen­dants are bet­ter pro­tected against harm­ful mu­ta­tions. If a mu­ta­tion de­stroys one copy of a gene, three oth­ers can take over. The big­gest ad­van­tage might be that the ex­tra genes could de­velop into new genes with other func­tions over time.

The genome dou­bling in flow­er­ing plant an­ces­tors con­se­quently laid the foun­da­tion of the ground-break­ing char­ac­ter­is­tics that trig­gered their suc­cess.

Flow­ers most im­por­tant event

To­day, the flow­er­ing plants are not just the most species-rich group of plants, but also the most di­verse. It in­cludes any­thing from the only 2-mm-wide mem­bers of the duck­weed fam­ily to the more than 100-m-high Aus­tralian giant eu­ca­lyp­tus.

Fur­ther­more, the suc­cess is em­pha­sised by the fact that sci­en­tists have not yet found fos­sils of pre­his­toric flower fam­i­lies, which have gone ex­tinct at a later point in time. In other words, the com­bi­na­tion of flow­ers, nec­tar, and co­op­er­a­tion with in­sects was so in­ge­nious that none of the larger groups of flow­ers, which have emerged over the past 140 mil­lion years, have ever dis­ap­peared again.

Flow­er­ing plants have adapted to life in the dri­est deserts of the world, on the high­est moun­tains, and on the ocean floor. And only a few en­vi­ron­ments on Earth are not com­pletely dom­i­nated by the suc­cess­ful plants. Gym­nosperm conifers are still the most nu­mer­ous in north­ern forests. But it is not by far un­think­able that the flow­er­ing plants will at some point be­come able to out com­pete the die-hard conifers on their own home turf.

The com­plete dom­i­nance of the plant king­dom and the huge in­flu­ence on the world’s fauna has made some palaeon­tol­o­gists point out the first flower’s emer­gence as one of the most im­por­tant events in Earth’s his­tory. Over a pe­riod of 40 mil­lion years, dur­ing the hey­day of the dinosaurs, the small growths man­aged to al­ter life in the world, pre­par­ing the plant and an­i­mal groups that rule the world to­day for suc­cess. Not even the huge me­teor that struck Earth 66 mil­lion years ago, wip­ing out the dinosaurs, was able to change what the flow­ers had pro­duced.


The first flower, which emerged in the era of the dinosaurs, prob­a­bly had a di­am­e­ter of less than 1 cm.

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