Tilgangur þessara skrifa er að reyna að útrýma leiðum rangskilningi, sem mikið hefur borið á í ritum manna hér á landi hin síðari ár, jafnt í fræðigreinum sem kennslubókum.
Sem kunnugt er byggist tvínafnakerfið í flokkunarfræði á því, að sérhver einstaklingur plöntu- og dýraríkis ber ákveðið tegundarnafn,
sem er tvö heiti (t.d. Ranunculus acris). Fyrra nafnið er ættkvíslarnafn og hið síðara viðurnafn. Sá ruglingur er alls ráðandi, að aðeins seinna nafnið, viðurnafnið (t.d. acris), er kallað tegundarheiti. Það væri hægur vandi að tiltaka mýmörg dæmi, en því skal sleppt. Hvað við kemur síðara orðinu, hef eg valið að nefna það viðurnafn (á ensku »specific epithet«), en vera má að önnur orð komi til greina. Skal nú vikið fáum orðum að bakgrunni tvínafnakerfisins, sem jafnan er kennt við sænska grasafræðinginn Carl von Linné (1707-1778).
Á tímum Grikkja og Rómverja leituðust menn við að flokka plöntur og dýr eigi síður en nú á dögum. Elzta flokkunarkerfið, sem vitað er um, er kennt við hinn vísa Theophrastos, nemanda Aristotelesar. Í verki sínu Historia plantarum lýsti hann 480 plöntum, sem hann flokkaði eftir ýmsum útlitseinkennum. Af Rómverjum má nefna Plinius hinn eldri, en hann lýsti um 1’000 tegundum plantna í Historia naturalis.
Í þá tíð og fram á miðaldir var oftast notað aðeins eitt nafn fyrir hverja plöntutegund. Fyrir kom þó, að einu orði eða fleirum væri bætt við til þess að kveða nánar á um tegundina. Einkum voru notuð orð, sem lýstu vaxtarstað, lit, heimkynnum eða einhverju því um líku. Eftir því sem tegundum fjölgaði urðu nöfnin sífellt lengri, því að oftast var orði bætt við gamalt nafn til þess að aðskilja nýja tegund. Nafn einnar tegundar gat því verið óslitin röð af mörgum lýsingarorðum (nomina specifica) eins og Urtica urens pilulas ferens og Cardamine alpina minor resedae foliis eru dæmi um.
Í fyrstu notaði Linné röð af lýsingarorðum til þess að nafngreina tegundir eins og þá var háttur manna. Í plöntuskrám frá árunum 1745 og 1749 byrjar hann að nota tvínafnakerfi samhliða gömlum nöfnum. Í Philosophia botanica (1751) setur hann fram í fyrsta skipti nokkrar meginreglur um nafngiftir plantna, meðal annars um viðurnafnið (nomen triviale), sem á að vera aðeins eitt orð (vocabulum unicum). Þar er einnig kveðið á um, að hvorki tvær ættkvíslir né tvær tegundir geti haft sama nafn, svo og að halda beri í gamla nafnið, ef einni ættkvísl er skipt í tvær eða fleiri. Í Species plantarum frá 1753 er tegundanöfnum samkvæmt tvínafnakerfi bætt inn á spássíur, en það er ekki fyrr en í 10. útgáfu af Systema naturae (1758), sem farið er að nota það um dýr, þá jafnframt samhliða gömlum nöfnum.
Fyrir daga Linnés komu tvínefni oft fyrir af eðlilegum ástæðum, þegar ekki var þörf á nema tveimur orðum. Í verkum nokkurra manna má sjá, að þeir reyndu af fremsta megni að sporna við löngum nöfnum. Í því sambandi má geta bræðranna Jean Bauhin (1541-1631) og Gaspard Bauhin (1560-1624), Joseph Pitton de Tournefort (1656-1708) og John Ray (1628-1705). Meðal annars hefur því verið fram haldið, að þessir menn, einkum hinn síðast nefndi, hafi lagt grunninn að tvínafnakerfinu. Að vísu fær þetta hvergi staðizt, ef það skilyrði er sett, að tegundarnafnið sé undantekningarlaust ættkvíslarheiti og viðurnafn. Geta má þess einnig, að á öðrum og þriðja áratug þessarar aldar héldu sumir dýrafræðingar því fram, að tvínöfnin væru nöfn á flokkunareiningum á þá leið, að fyrra nafnið væri ættkvíslin en hið síðara tegundin. Spunnust um þetta talsverðar deilur og urðu margir til þess að mótmæla þessum skilningi (sjá m.a. Poche, 1927 í »Entomologische Zeitschrift« nr. 41).
Tvínafnakerfi Linnés hlaut fljótt almenna viðurkenningu meðal grasa- og dýrafræðinga. Fljótlega fóru einstakir menn að leggja til ýmsar breytingar og síðar var farið að fjalla um tvínafnakerfið á alþjóðaþingum. Dýrafræðingar urðu fyrri til að samþykkja grundvallarreglur sínar á árunum frá 1842 til 1845. Á alþjóðaþingi grasafræðinga í París 1867 samþykktu grasafræðingar fyrsta nafngiftakerfið um plöntur. Tvínafnakerfið hefur iðulega síðan verið til umræðu á þingum náttúrufræðinga og hafa ýmsar breytingar verið gerðar á því í tímans rás. Nú eru starfandi alþjóðlegar nefndir, sem sjá um að nafnareglum sé fylgt.
Þetta greinarkorn er orðið lengra en ætlað var í fyrstu. Hér var aldrei ætlun að ræða um tvínafnakerfið í smáatriðum, heldur einungis að vekja athygli á því, að tegundarnafn er tvö heiti: ættkvíslarnafn + viðurnafn. Von mín er, að með þessari ábendingu verði hvimleiður misskilningur úr sögunni.
Grein þessi birtist í Náttúrufræðingnum 62. ár, 1.-2. hefti: 35-36.
Leitarorð: epitet • flokkunareining • flokkunarkerfi • Gaspard Bauhin • Joseph Pitton de Tournefort • linné • Philosophia botanica • Plinius hinn eldri • plöntunöfn • Systema naturae • tegund • tegundarnafn • tvínafnakerfi • Tvínafnakerfi Linnés • viðurnafn • ættkvíslarnafn
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