Lygodium hians E.Fournier (Pteridophyta, Schizaeales) — an endemic unusual ground-clothing member of a modern climbing fern genus in New Caledonia

[摘要] Acolonyofafern,LygodiumhiansE.Fournier(Schizaeales),studiedonthesouthwestPacificIslandofNewCaledonia,displaysagrowthformunusualforanymemberofthisgenus.OtherlivingspeciesofthegenusLygodiumSw.arecharacterizedbytwiningfronds,withindefinitegrowth,whichclimbextensivelyonthesupportprovidedbyothernearbyvegetation.Thesefrondscanarisefromasearlyasthesporelingstageandfulfilbothvegetativeandreproductivefunctions,withsporesproducedinlateralsorophoresintheupperpartsofthefronds.Bycontrast,inL.hians,climbingfrondsareonlyrarelyproducedandthesecarryterminaltosubterminalsorophores.Themainvegetativegrowthisofalow-growing(heretermed‘ground-clothing')frond-type,ofdefinite,ratherthanindefinite,growthandofunusualdichotomousbladestructure.Thislifeformhassurvived,inthisrareandlittleknownremotespecies,underconditionsofconsiderableecological,aswellasgeographic,isolationinthemountainsofNewCaledonia.Blade/pinnuleabscissionoccursinL.hiansinbothground-clothingandclimbingfronds,thereforeshedfoliarunitsinthefossilrecorddonotimplythatancientLygodiumwereclimbers.ThefeaturesofL.hians,uniquelywithinLygodium,providemorphologicallinkswithSchizaeaSm.andActinostachysWall.ThemorphologyconsiderablyexpandsourconceptofvariationinthegenusLygodiumandsuggeststhatthislifeformtodaymayrepresentanevolutionaryphaseneartotheearlystagesofdiversificationofthegenus.ForthesereasonsL.hiansisworthyofinclusioninfuturemolecularandmorphologicalphylogeneticanalysesandshouldbeincorporatedincomparativestudiesbypalaeobotanistsstudyingfossilferns.

[学科分类] 植物学

[关键词] Schizaeales;Lygodiaceae;ground-clothing fern;New Caledonia;morphology;Lygodium evolution;Schizaeales;Lygodiaceae;fougère couvre-sol;Nouvelle-Calédonie;morphologie;évolution de Lygodium