In the nation­al park area, exten­sive exam­i­na­tions of the fau­na and flo­ra were car­ried out until 1998. A total of 1,726 plant species were iden­ti­fied, which can be grouped into 90 types of veg­e­ta­tion and 44 plant com­mu­ni­ties, 12 of which are aquat­ic plant com­mu­ni­ties. Of the 1,726 iden­ti­fied plant species, 303, i.e. 17.6 %, on the Red List of Endan­gered Ferns and Flow­er­ing Plants of the State of Bran­den­burg, 38 of which belong to Cat­e­go­ry 1, i.e. to the species direct­ly threat­ened with extinc­tion. Among them are the moun­tain asters (Aster amel­lus), the bristly and broad-leaved bell­flower (Cam­pan­u­la cer­vi­caria and Cam­pan­u­la lat­i­fo­lia), the Pen­te­cost car­na­tion (Dianthus gra­tia­nop­o­li­tanus), the wire-haired ele­phant (Inu­la hir­ta), the moun­tain herb (Liban­otis mon­tana), the pur­ple orchid (Orchis pur­purea) or the species that were recent­ly record­ed in Bran­den­burg for the first time, such as yel­low-sheathed feath­er grass (Sti­pa pul­cher­ri­ma) and the downy oak (Quer­cus pubes­cens), which have their only Bran­den­burg loca­tion in the low­er Oder val­ley. 149 species are list­ed as threat­ened on the Red List of the Fed­er­al Repub­lic of Ger­many. The high pres­ence of these threat­ened plant species shows the impor­tance of the project area for species and biotope pro­tec­tion. Almost every sixth Red List species in the fed­er­al ter­ri­to­ry and 44.5% of the Red List species in the State of Bran­den­burg occur in the low­er Oder val­ley, with the species threat­ened being even­ly dis­trib­uted between the wet and dry locations.

The Fed­er­al Repub­lic of Ger­many bears a spe­cial respon­si­bil­i­ty for the preser­va­tion of 14 plant species grow­ing in the project area, as these occur exclu­sive­ly or almost exclu­sive­ly here, with a decreas­ing trend. For exam­ple, four out of five known sites of sand feath­er grass in Ger­many and Bran­den­burg are here (Sti­pa borys­theni­ca). The con­ser­va­tion of this feath­er grass species is only pos­si­ble here and in adja­cent areas. It is there­fore one of the most impor­tant species in the area in terms of nature conservation.

As a result of a sum­ma­riz­ing, nature con­ser­va­tion assess­ment, it can be stat­ed that the rare plant com­mu­ni­ties can be found pre­dom­i­nant­ly in the arid areas of the hill coun­try and in the Oder foothills, while more fre­quent plant com­mu­ni­ties can be found in the polders.

The low­er Oder val­ley is also of out­stand­ing impor­tance for plant-geo­graph­i­cal rea­sons. With the flat-leaved man lit­ter (Eryn­gium planum), the glossy milk­weed (Euphor­bia luci­da) and the Tatar catch­fly (Silene tatar­i­ca) flow val­ley plants from the con­ti­nen­tal areas of Europe and Asia reach the Oder val­ley and are found here just like, for exam­ple, the adder’s head hawk­weed (Hieraci­um echioides) and the Siber­ian bell­flower (Cam­pan­u­la sibir­i­ca) the absolute west­ern lim­it of their Euro­pean dis­tri­b­u­tion in the dry grass­land. With the occur­rence of these species, the above-described con­ti­nen­tal cli­mat­ic influ­ences are doc­u­ment­ed floristically.

The sand car­na­tion, which is only found in North­ern Europe (Dianthus are­nar­ius) reach­es its south­west bor­der in the low­er Oder val­ley. The loca­tion around Gartz, which is rich in indi­vid­u­als, is of par­tic­u­lar impor­tance through­out Germany.

In con­trast, a num­ber of species of the bore­al-cir­cum­po­lar species are present in acidic forests and in the nutri­ent-rich silt­ing bogs. This sub­head­ing includes many win­ter­green plants (Pyrolo­ceae), some sedge plants (Cyper­aceae), for exam­ple the even rel­a­tive­ly com­mon beak sedge and the blad­der sedge (Carex ros­tra­ta, Carex vesi­caria) or the swamp heart leaf, which blooms so beau­ti­ful­ly in sum­mer (Par­nas­sia palus­tris), which, con­trary to its name, can be found main­ly on dry grass­lands in the low­er Oder valley.

There are no longer any real “Atlanti­cists” on the low­er Oder, because the tem­per­a­ture in the annu­al mean and the amount of pre­cip­i­ta­tion already dif­fer great­ly from the sea cli­mate. Only a few sub-Atlantic-Nordic species can also be found in the low­er Oder val­ley. These include the sil­ver grass (Corynepho­rus canescens), the broom (Sarotham­nus sco­par­ius), the hair gorse (Genista pilosa), the for­est sedge and the sand sedge (Carex syl­vat­i­ca and Carex are­nar­ia), the com­mon heather (Cal­lu­na vul­garis) and the ear­ly Hafer­schmiele (Aira prae­cox).

There are only a few species of sub-Mediter­ranean plants, but they have a clear cen­ter of abun­dance in the low­er Oder val­ley, many hun­dreds of kilo­me­ters from their closed range. As such, the pur­ple orchid (Orchis pur­purea) and the downy oak recent­ly found on the Ger­man side of the Oder (Quer­cus pubes­cens) to call.

On the oth­er hand, there is a large group of plants that are com­mon both in the East­ern Euro­pean plant com­mu­ni­ties and in the dry forests and dry grass­lands of south­ern Europe. In addi­tion to the ones already men­tioned, these include such rare species as the showy and famous spring Ado­nis (Ado­nis ver­nalis), the cross gen­tian (Gen­tiana cru­ci­a­ta), the pur­ple sal­si­fy (Scor­zon­era pur­purea), the great anemone (Anemone sylvestris), some sum­mer root species (Orobanche pur­purea, Orobanche lutea and Orobanche are­nar­ia), the shag­gy flag vetch (Oxytro­pis pilosa), the deer root, which blooms so mag­nif­i­cent­ly in autumn (Peucedanum cer­varia) or the ser­vice tree (Sor­bus tormi­nalis), which as a tree can reach an enor­mous age.

Two mon­tane decid­u­ous for­est species are to con­clude the plant-geo­graph­i­cal part: The Christoph­skraut (Actaea spi­ca­ta), which flow­ers at the end of May, and the Zwiebel-Zah­n­wurz (Den­taria bulb­ifera) with its small brown­ish-pur­ple brood bulbs in the leaf axils. They are only found in very nat­u­ral­ly estab­lished maple and beech forests.

Even more inter­est­ing than the indi­vid­ual plant species are the plant com­mu­ni­ties com­posed accord­ing to the biot­ic and abi­ot­ic fac­tors. Despite numer­ous indi­vid­ual works on the Ger­man and Pol­ish side, no com­plete mono­graph­ic study has yet been pub­lished. 115 asso­ci­a­tions have been record­ed so far.

In the nat­ur­al back­wa­ter remains of the Oder flood­plain, the pools, the canals and the ditch­es, aquat­ic plant com­mu­ni­ties can be found that have sig­nif­i­cant­ly improved in qual­i­ty in recent years as a result of decreas­ing anthro­pogenic influ­ences. So emerged with the thread pondweed (Pota­moge­ton fil­i­formis) revived a species that had long dis­ap­peared in the area. Some water root soci­eties with the root­less duck­weed (Wolf­fia arrhiza) or with the swim­ming fern (Salvinia natans). The often tight­ly closed stocks of water lilies offer the observ­er an aes­thet­i­cal­ly pleas­ing sight, but are rel­a­tive­ly poor in species. The large float­ing leaves of the water lily dark­en the sub­merged hydroflo­ra and thus pre­vent its devel­op­ment, espe­cial­ly since the depth of vis­i­bil­i­ty of the water in eutroph­ic bogs is already low.

Reeds are rare in the Oder Val­ley because the cor­re­spond­ing shal­low water zones with their silt­ing areas are large­ly lack­ing. Only the reed beds of swan flow­ers are more com­mon, espe­cial­ly at the riv­er edges in the direct riv­er area of the Oder and fall in sum­mer due to the bright pink inflo­res­cences of the swan flower, which often appear in large num­bers (Buto­mus umbel­la­tus) espe­cial­ly on. Even the plumes of water (Glyc­e­ria max­i­ma) can dom­i­nate on mud banks, sed­i­ment­ed ponds or oth­er exca­va­tions with strong­ly fluc­tu­at­ing water levels.

As a rule, the waters in the pold­ers are bound­ed by nitrophilic ripar­i­an peren­ni­als and fring­ing com­mu­ni­ties, which are defin­ing struc­tur­al ele­ments in the pold­er land­scape. The bindweed angel­i­ca soci­ety with its huge umbel inflo­res­cences of the real angel­i­ca (Angel­i­ca archangel­i­ca) as a spe­cial­ist soci­ety requires high water lev­els all year round with low flow speeds and a good sup­ply of nutri­ents. Above the mean water line it is replaced by the net­tle silk winch soci­ety, in which the tree silk (Cus­cu­ta lupuli­formis) and the hop silk (Cus­cu­ta europaea), both root­less and leaf­less par­a­sites, wind up on the shoot axes of the oth­er tall peren­ni­als and often depress them in autumn. On the oth­er hand, the bank fringes can also be cov­ered with wil­low bush­es or indi­vid­u­al­ly or in groups stand­ing tree-shaped white wil­lows, which rep­re­sent a spe­cial type of veg­e­ta­tion in the area of the soft­wood flood­plains. In pure­ly for­mal terms, these stocks can be clas­si­fied as rem­nants of soft­wood allu­vial for­est. How­ev­er, this would be in stark con­trast to the real allu­vial forests, because with these stands there is hard­ly a for­est cli­mate and there­fore eco­log­i­cal­ly com­plete­ly dif­fer­ent con­di­tions are giv­en. It would be bet­ter to define a sep­a­rate biotope type for these stocks and to des­ig­nate it as a Cen­tral Euro­pean “gallery for­est”, anal­o­gous to sim­i­lar­ly struc­tured stocks, for exam­ple in savan­nas or steppe areas.

The actu­al pold­er areas are large­ly free of forests. More exten­sive sedge mead­ows can be found in the north­ern part of the Fid­di­chow­er Pold­er. The char­ac­ter­is­tic soci­ety of the pold­ers and the fore-dike areas are reed grass beds, which are made up of reed grass (Phalaris arun­d­i­nacea) can be mas­tered. Depend­ing on their loca­tion in rela­tion to the cur­rent or the dura­tion of the flood­ing, they can be designed very dif­fer­ent­ly. They con­tain some of the riv­er val­ley plants char­ac­ter­is­tic of Bran­den­burg, such as the wil­low leaf yarrow (Achil­lea sali­ci­fo­lia), the cat’s tail (Leonu­rus mar­ru­bi­as­trum) or the mead­ow ele­phant (Inu­la bri­tan­ni­ca) opti­mal grow­ing con­di­tions. Fox­tail mead­ows have formed on high­er-lying loca­tions, but as a result of their inten­sive use, they still give a less nat­ur­al impres­sion and are in some cas­es even rud­er­al­ized due to overuse. If these loca­tions are used exten­sive­ly, and espe­cial­ly if the mow­ing is sin­gle in late sum­mer, the con­ti­nen­tal red cone and pipe grass mead­ow (Vio­lo — Cni­di­etum), which is gen­er­al­ly rare in Europe, is devel­oped on such loca­tions. Tar­get­ed biotope man­age­ment in recent years has made it pos­si­ble to secure their remain­ing stocks. They are even expand­ing at the moment.

At approx­i­mate­ly the same mois­ture lev­el, after these types of mead­ow have been aban­doned, a mead­ow-like high herba­ceous mead­ow devel­ops, which is main­ly made up of glossy milk­weed (Euphor­bia luci­da) is mas­tered. From the large, yel­low pseu­do-inflo­res­cences of the milk­weed in ear­ly sum­mer to the blue inflo­res­cences of the asters in autumn, this plant com­mu­ni­ty is one of the high­lights of the veg­e­ta­tion of the low­er Oder valley.