论西藏蒿属植物区系

<正>inxizangthereare57speciesand6varietiesunderthegenusartemisialinn,whichcanbedividedinto2subgeneraand6sections(seep.82-85).sect.absinthiumofthegenusartemisiaispossiblythemostprimitive,becausetheheadsarebiggerandtheflowersonaheadarenumerous,over40-100-theinnermostflowersofthediskaresterile,thecorollaoftheouterflower(margine)issimilartotheinneroneswith4(not2)corolla-teeth.sometimestherearesterileandroeciaintheouterflowers.thereceptacleiscoveredwithhairswhicharedevelopedfromthescalesinthespeciesoftribusheliantheae.sect.abrotanumarisingfromsect.absinthiumistheintermediatewithglabrousreceptacle,andtheadvancedsect.artemisiamayhavearisenfromabrotanum.inthissect,headsaresmallandflowersoneachheadarenotverymany(<20).insouth-westchina(aplantrefugeintheageoficeofthequaternary),sect.viscidipubesy.r.lingmayhavearisenfromsect.artemisiaorsect.abrotanum,andhasallthestems,branches,leavesandbractsoftheheadsclothedwithglandular-hairs.withtheexceptionofsubgenusdracunculusarisingfromsubgenusartemisia,sect.latilobusy.r.lingpossesesbroaderleaflobesandoftenoccursintheforest,whilesect.dracunculusproducesnarrowerleaflobesandoftenoccursinthesteppeordesert-steppe.sect.artemisiainxizangmigratedfromtheoriginalcentreofthegenus,whichoccuredpossiblyinthemountainregionsofn.asiabythemiddleoftertiaryperiodandatthebeginningofquaternaryperiod.theymigratedacrossc.asia(east)-mongolia(west),orthroughthesichuan-yunnanplateausecondaryoriginalcentreintoxizangandevengaverisetomanyendemicspeciesofxizang(forthedevelopmentsystemofartemisiaseefig.1).thefloristicalelementsofartemisiainxizangaresodiversethattheyaretobesummarizedasfollows:(tablel)1.holartic(subholartic)subkingdom.(1)tertiaryancientendemicspecies.2.eurasiasteppeorsemidesert-steppesubkingdom.