Thorough understanding of biodiversity is a fundamental prerequisite for biological research. A lack of taxonomic knowledge and species misidentifications are particularly critical for conservation. Here we present an example of Potamogeton floridanus, the Florida Pondweed, an endangered taxon endemic to a small area in the Florida panhandle, whose taxonomic status remained controversial for more than a century, and all previous attempts to elucidate its identity have failed. We applied molecular approaches to tackle the origin of the mysterious taxon and supplemented them with morphological and anatomical investigations of both historical herbarium collections and plants recently collected in the type area for a comprehensive taxonomic reassessment. Sequencing of two nuclear ribosomal markers and one chloroplast non-coding spacer resulted in the surprising discovery that P. floridanus is a hybrid of P. pulcher and P. oakesianus, with the former being the maternal parent. The hybrid colony is currently geographically isolated from the distribution range of P. oakesianus. We show that previous molecular analyses have failed to reveal its hybrid identity due to inadequate nuclear DNA sequence editing. This is an example how the uncritical use of automized sequence reads can hamper molecular species identifications and also affect phylogenetic tree construction and interpretation. This unique hybrid taxon, P. ×floridanus, adds another case study to the debate on hybrid protection; consequences for its conservation are discussed.

Department of Biology Massachusetts College of Liberal Arts North Adams Massachusetts United States of America

Department of Botany Faculty of Science Charles University Prague Czech Republic

The Czech Academy of Sciences Institute of Botany Průhonice Czech Republic

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Raduski AR, Rieseberg LH, Strasburg JL. Effective population size, gene flow, and species status in a narrow endemic sunflower, Helianthus neglectus, compared to its widespread sister species, H. petiolaris. Int J Mol Sci. 2010; 11: 492–506. doi: 10.3390/ijms11020492 PubMed DOI PMC

Oakley CG. The influence of natural variation in population size on ecological and quantitative genetics of the endangered endemic plant Hypericum cumulicola. Int J Plant Sci. 2014; 176: 11–19.

Sedlacek J, Schmid B, Matthies D, Albrecht M. Inbreeding depression under drought stress in the rare endemic Echium wildpretii (Boraginaceae) on Tenerife, Canary Islands. PLoS ONE. 2012; 7: e47415 doi: 10.1371/journal.pone.0047415 PubMed DOI PMC

Alonso C, García-Sevilla M. Strong inbreeding depression and individually variable mating system in the narrow endemic Erodium cazorlanum (Geraniaceae). An Jard Bot Madr. 2013; 70: 72–80.

González MEG, Redondo RA, Saiz EA, Valcarce RG, García SA, Jiménez NF. Conservation status and protection measures for Draba hispanica Boiss. subsp. lebrunii P. Monts., endemic to the Altocarrionés subsector (Castile and Leon, Spain). Acta Bot Gall. 2011; 158: 577–594.

Wang B, Ma Y, Chen G, Li C, Dao Z, Sun W. Rescuing Magnolia sinica (Magnoliaceae), a Critically Endangered species endemic to Yunnan, China. Oryx. 2016; 50: 446–449.

Zaya DN, Molano-Flores B, Feist MA, Koontz JA, Coons J. Assessing genetic diversity for the USA endemic carnivorous plant Pinguicula ionantha R.K. Godfrey (Lentibulariaceae). Conserv Genet. 2017; 18: 171–180.

Wiegleb G, Kaplan Z. An account of the species of Potamogeton L. (Potamogetonaceae). Folia Geobot. 1998; 33: 241–316.

Kaplan Z. Hybridization of Potamogeton species in the Czech Republic: diversity, distribution, temporal trends and habitat preferences. Preslia 2010; 82: 261–287.

Kaplan Z, Štěpánek J. Genetic variation within and between populations of Potamogeton pusillus agg. Pl Syst Evol. 2003; 239: 95–112.

Kaplan Z, Fehrer J, Hellquist CB. New hybrid combinations revealed by molecular analysis: The unknown side of North American pondweed diversity (Potamogeton). Syst Bot. 2009; 34: 625–642.

Kaplan Z, Uotila P. Potamogeton × exilis (P. alpinus × P. natans), a new hybrid pondweed from Finland. Nord J Bot. 2011; 29: 477–483.

Kaplan Z. Phenotypic plasticity in Potamogeton (Potamogetonaceae). Folia Geobot. 2002; 37: 141–170.

Hettiarachchi P, Triest L. Isozyme polymorphism in the genus Potamogeton (Potamogetonaceae). Opera Bot Belg. 1991; 4: 87–114.

Kaplan Z, Jarolímová V, Fehrer J. Revision of chromosome numbers of Potamogetonaceae: a new basis for taxonomic and evolutionary implications. Preslia 2013; 85: 421–482.

Preston CD. Pondweeds of Great Britain and Ireland. London: Botanical Society of the British Isles; 1995.

Dandy JE. Potamogeton L In: Tutin TG, Heywood VH, Burges NA, Moore DM, Valentine DH, Walters SM, Webb DA, editors. Flora Europaea. Vol. 5 Cambridge: Cambridge University Press; 1980. pp. 7–11.

Kashina LI. Potamogetonaceae In: Krasnoborov IM, editor. Flora of Siberia. Vol. 1 (Lycopodiaceae–Hydrocharitaceae). Enfield & Plymouth: Science Publishers; 2000. pp. 85–99.

Guo Y-H, Haynes RR, Hellquist CB, Kaplan Z. Potamogetonaceae In: Wu Z-Y, Raven PH, Hong D-Y, editors. Flora of China. Vol. 23 (Acoraceae through Cyperaceae). St. Louis: Missouri Botanical Garden Press; 2010. pp. 108–115.

Wiegleb G. Potamogetonaceae In: Nooteboom HP, editor. Flora Malesiana. Ser. I. Vol. 16 Leiden: Nationaal Herbarium Nederland; 2002. pp. 174–196.

Papassotiriou SE, Jacobs SWL, Hellquist CB. Potamogetonaceae In: Wilson A, editor. Flora of Australia. Vol. 39 (Alismatales to Arales). Canberra: Australian Biological Resources Study; 2011. pp. 84–95.

Haynes RR, Hellquist CB. Potamogetonaceae Dumortier In: Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Vol. 22 New York: Oxford University Press; 2000. pp. 47–74.

Haynes RR, Holm-Nielsen LB. Potamogetonaceae In: Luteyn JL, Gradstein SR, editors. Flora Neotropica Monograph. Vol. 85 New York: New York Botanical Garden; 2003. pp. iv + 1–52.

Kaplan Z. Genus Potamogeton on the Svjatoj Nos isthmus and in the Barguzinskaja valley, Lake Baikal. Siber Nat (Praha). 1995; 1: 73–89.

Kaplan Z. Potamogeton schweinfurthii A. Benn., a new species for Europe. Preslia 2005; 77: 419–431.

Kaplan Z. Tiselius’ Potamogeton exsiccates: changes in taxonomy and nomenclature from one-century perspective. Ann Bot Fennici 2010; 47: 373–393.

Kaplan Z, Marhold K. Multivariate morphometric analysis of the Potamogeton compressus group (Potamogetonaceae). Bot J Linn Soc. 2012; 170: 112–130.

Kaplan Z, Symoens J-J. Taxonomy, distribution and nomenclature of three confused broad-leaved Potamogeton species occurring in Africa and on surrounding islands. Bot J Linn Soc. 2005; 148: 329–357.

Wiegleb G. Notes on pondweeds–outlines for a monographical treatment of the genus Potamogeton L. Feddes Repert. 1988; 99: 249–266.

Wiegleb G. A redescription of Potamogeton distinctus including remarks on the taxonomy of the Potamogeton nodosus group. Pl Syst Evol. 1990; 169: 245–259.

Wiegleb G. A redescription of Potamogeton wrightii (Potamogetonaceae). Pl Syst Evol. 1990; 170: 53–70.

Iida S, Kosuge K, Kadono Y. Molecular phylogeny of Japanese Potamogeton species in light of noncoding chloroplast sequences. Aquat Bot. 2004; 80: 115–127.

Lindqvist C, De Laet J, Haynes RR, Aagesen L, Keener BR, Albert VA. Molecular phylogenetics of an aquatic plant lineage, Potamogetonaceae. Cladistics. 2006; 22: 568–588. PubMed

Les DH, Murray NM, Tippery NP. Systematics of two imperiled pondweeds (Potamogeton vaseyi, P. gemmiparus) and taxonomic ramifications for subsection Pusilli (Potamogetonaceae). Syst Bot. 2009; 34: 643–651.

Wang QD, Zhang T, Wang JB. Phylogenetic relationships and hybrid origin of Potamogeton species (Potamogetonaceae) distributed in China: Insights from the nuclear ribosomal internal transcribed spacer sequence (ITS). Pl Syst Evol. 2007; 267: 65–78.

Zhang T, Wang QD, Li W, Cheng Y, Wang J. Analysis of phylogenetic relationships of Potamogeton species in China based on chloroplast trnT-trnF sequences. Aquat Bot. 2008; 89: 34–42.

Yang T, Zhang TL, Guo YH, Liu X. Testing eight barcoding markers for Potamogeton species at intraspecific levels. Aquat Bot. 2017; 137: 56–64.

Ito Y, Robledo GL, Iharlegui L, Tanaka N. Phylogeny of Potamogeton (Potamogetonaceae) revisited: Implications for hybridization and introgression in Argentina. Bull Natl Mus Nat Sci., ser. B, 2016; 42: 131–141.

Zalewska-Gałosz J, Ronikier M, Kaplan Z. The first European record of Potamogeton ×subobtusus identified using ITS and cpDNA sequence data. Preslia. 2009; 81: 281–292.

Kaplan Z, Fehrer J. Erroneous identities of Potamogeton hybrids corrected by molecular analysis of plants from type clones. Taxon. 2011; 60: 758–766.

Kaplan Z, Fehrer J. An orphaned clone of Potamogeton ×schreberi in the Czech Republic. Preslia. 2009; 81: 387–397.

Kaplan Z, Fehrer J, Hellquist CB. Potamogeton ×jacobsii (Potamogetonaceae) from New South Wales, Australia–the first Potamogeton hybrid from the Southern Hemisphere. Telopea. 2011; 13: 245–256.

Du Z-Y, Yang C-F, Chen J-M, Guo Y-H. Identification of hybrids in broad-leaved Potamogeton species (Potamogetonaceae) in China using nuclear and chloroplast DNA sequence data. Pl Syst Evol. 2010; 287: 57–63.

Zalewska-Gałosz J, Ronikier M, Kaplan Z. Discovery of a new, recurrently formed Potamogeton hybrid in Europe and Africa: molecular evidence and morphological comparison of different clones. Taxon. 2010; 59: 559–566.

Zalewska-Gałosz J, Ronikier M. Potamogeton ×maëmetsiae: a new hybrid of linear-leaved pondweeds from Central Europe. Preslia. 2011; 83: 265–279.

Bobrov AA, Zalewska-Gałosz J, Chemeris EV. Potamogeton ×clandestinus (P. crispus × P. natans, Potamogetonaceae), a new natural pondweed hybrid discovered in Europe. Phytotaxa. 2013; 149: 31–49.

Kaplan Z, Fehrer J. Molecular evidence for a natural primary triple hybrid in plants revealed from direct sequencing. Ann Bot. 2007; 99: 1213–1222. doi: 10.1093/aob/mcm072 PubMed DOI PMC

Morong T. A new species of Potamogeton. Bull Torrey Bot Club. 1886; 13: 145.

Small JK. Flora of the southeastern United States. New York; 1903.

Graebner P. Potamogeton (Tourn.) L. In: Engler A, editor. Das Pflanzenreich, Regni vegetabilis conspectus. Vol. 31 (IV.11). Leipzig: Wilhelm Engelmann; 1907. pp. 39–142 & 161–162.

Taylor N. Zannichelliaceae. In: Britton NL, Underwood LM, editors. North American Flora. Vol. 17(1). New York; 1909. pp. 13–27.

Bennett A. Notes on Potamogeton. J Bot (London). 1907; 45: 373–377.

Bennett A. Revision of the Australian species of Potamogeton. J Bot (London). 1887; 25: 177–179.

Bennett A. Notes on Japanese potamogetons. Bull Herb Boiss n s. 1896; 4: 545–549.

Bennett A. [Enumeration of all the plants known from China …] Potamogeton. J Linn Soc, Bot. 1903; 36: 193–196.

Bennett A. The potamogetons of the Philippine Islands. Philipp J Sci, C Bot. 1914; 9: 339–344.

Hagström JO. Critical researches on the Potamogetons. Kungl Svenska Vetenskapsakad Handl. 1906; 55(5): 1–281.

Ogden EC. The broad-leaved species of Potamogeton of North America north of Mexico. Rhodora. 1943; 45: 57–105, 119–163 & 171–214.

Wilhelm GS, Mohlenbrock RH. The rediscovery of Potamogeton floridanus Small (Potamogetonaceae). Sida. 1986; 11: 340–346.

Kaplan Z, Reveal JL. Taxonomic identity and typification of selected names of North American Potamogetonaceae. Brittonia. 2013; 65: 452–468.

Fish US and Service Wildlife. Federal threatened, endangered, and other species of concern likely to occur in the Florida Panhandle Panama City Fish and Wildlife Service, Panama City, FL; 2013. Available from: http://www.fws.gov/panamacity/resources/pdf/Species%20Lists/TEST%20Species%20List%202013%20Panhandle.pdf. Accessed March 2015.

Florida Natural Areas Inventory. FNAI–Element tracking summary. 2014. Available from: http://www.fnai.org/PDF/Element_tracking_summary_current.pdf. Accessed March 2015.

US Fish and Wildlife Service. Endangered and Threatened Wildlife and Plants; Review of Plant Taxa for Listing as Endangered or Threatened Species. Federal Register. 1993; 58(188): 51144–51190.

Walter KS, Gillett HJ, editors. 1997 IUCN Red List of threatened plants. Gland: IUCN; 1998.

Hollingsworth PM, Gornall RJ, Preston CD. Genetic variability in British populations of Potamogeton coloratus (Potamogetonaceae). Pl Syst Evol. 1995; 197: 71–85.

Hollingsworth PM, Preston CD, Gornall RJ. Lack of detectable isozyme variability in British populations of Potamogeton epihydrus (Potamogetonaceae). Aquat Bot. 1996; 60: 433–437.

Hollingsworth PM, Preston CD, Gornall RJ. Isozyme evidence for hybridization between Potamogeton natans and P. nodosus (Potamogetonaceae) in Britain. Bot J Linn Soc. 1995; 117: 59–69.

Hollingsworth PM, Preston CD, Gornall RJ. Isozyme evidence for the parentage and multiple origins of Potamogeton × suecicus (P. pectinatus × P. filiformis, Potamogetonaceae). Pl Syst Evol. 1996; 202: 219–232.

Kaplan Z, Plačková I, Štěpánek J. Potamogeton ×fluitans (P. natans × P. lucens) in the Czech Republic. II. Isozyme analysis. Preslia. 2002; 74: 187–195.

Fant JB, Preston CD. Genetic structure and morphological variation of British populations of the hybrid Potamogeton × salicifolius. Bot J Linn Soc. 2004; 144: 99–111.

Kaplan Z, Wolff P. A morphological, anatomical and isozyme study of Potamogeton ×schreberi: confirmation of its recent occurrence in Germany and first documented record in France. Preslia. 2004; 76: 141–161.

Štorchová H, Hrdličková R, Chrtek J Jr, Tetera M, Fitze D, Fehrer J. An improved method of DNA isolation from plants collected in the field and conserved in saturated NaCl/CTAB solution. Taxon. 2000; 49: 79–84.

Nieto Feliner G, Rosselló JA. Better the devil you know? Guidelines for insightful utilization of nrDNA ITS in species-level evolutionary studies in plants. Mol Phylogen Evol. 2007; 44: 911–919. PubMed

Kaplan Z, Fehrer J. C omparison of natural and artificial hybridization in Potamogeton. Preslia. 2006; 78: 303–316.

Kaplan Z, Fehrer J. Molecular identification of hybrids from a former hot spot of Potamogeton hybrid diversity. Bot. 2013; 105: 34–40.

Kaplan Z, Fehrer J. E vidence for the hybrid origin of Potamogeton ×cooperi (Potamogetonaceae): traditional morphology-based taxonomy and molecular techniques in concert. Folia Geobot. 2004; 39: 431–453.

Fehrer J, Krak K, Chrtek J Jr. Intra-individual polymorphism in diploid and apomictic polyploid hawkweeds (Hieracium, Lactuceae, Asteraceae): disentangling phylogenetic signal, reticulation, and noise. BMC Evol Biol. 2009; 9: 239 doi: 10.1186/1471-2148-9-239 PubMed DOI PMC

Hall TA. BioEdit, a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucleic Acids Symp Ser. 1999; 41: 95–98.

Borchsenius F. FastGap 1.2. Department of Biosciences, Aarhus University, Denmark; 2009. Available from: http://www.aubot.dk/FastGap_home.htm.

Simmons MP, Ochoterena H. Gaps as characters in sequence-based phylogenetic analyses. Syst Biol. 2000; 49: 369–381. PubMed

Swofford DL. PAUP*: Phylogenetic analysis using parsimony (*and other methods), version 4 Sunderland: Sinauer; 2002.

Ronquist F, Huelsenbeck JP. MrBayes 3: Bayesian phylogenetic inference under mixed models. Bioinformatics. 2003; 19: 1572–1574. PubMed

Posada D, Crandall KA. Modeltest: testing the model of DNA substitution. Bioinformatics. 1998; 14: 817–818. PubMed

Raunkiær C. Anatomical Potamogeton-studies and Potamogeton fluitans. Bot Tidssk. 1903; 25: 253–280.

Fischer G. Die bayerischen Potamogetonen und Zannichellien. Ber Bayer Bot Ges. 1907; 11: 20–162.

Kaplan Z. Neotypification of Potamogeton ×fluitans Roth and the distribution of this hybrid. Taxon. 2005; 54: 822–826.

Kaplan Z, Symoens J-J. Proposal to conserve the name Potamogeton schweinfurthii A. Benn. (Potamogetonaceae) with a conserved type. Taxon. 2004; 53: 837–838.

Wiegleb G. The importance of stem anatomical characters for the systematics of the genus Potamogeton L. Flora (Jena). 1990; 184: 197–208.

Symoens JJ, van de Velden J, Büscher P. Contribution a l’étude de la taxonomie et de la distribution de Potamogeton nodosus Poir. et P. thunbergii Cham. et Schlechtend. en Afrique. Bull Soc Roy Bot Belgique. 1979; 112: 79–95.

Kaplan Z. Potamogeton ×fluitans (P. natans × P. lucens) in the Czech Republic. I. Morphology and anatomy. Preslia. 2001; 73: 333–340.

Dandy JE. Potamogeton L In: Stace CA, editor. Hybridization and the flora of the British Isles. London: Academic Press; 1975. pp. 444–459.

Kaplan Z. First record of Potamogeton × salicifolius for Italy, with isozyme evidence for plants collected in Italy and Sweden. Pl Biosystems. 2007; 141: 344–351.

Preston CD. Potamogeton L In: Stace CA, Preston CD, Pearman DA, editors. Hybrid flora of the British Isles. Bristol: Botanical Society of Britain and Ireland; 2015. pp. 319–332.

Preston CD, Bailey JP, Hollingsworth PM. A reassessment of the hybrid Potamogeton × gessnacensis G. Fisch. (P. natans × P. polygonifolius, Potamogetonaceae) in Britain. Watsonia. 1998; 22: 61–68.

Figuerola J, Green AJ, Santamaría L. Comparative dispersal effectiveness of wigeongrass seeds by waterfowl wintering in south-west Spain: quantitative and qualitative aspects. J Ecol. 2002; 90: 989–1001.

Santamaría L, Charalambidou I, Figuerola J, Green AJ. Effect of passage through duck gut on germination of fennel pondweed seeds. Arch Hydrobiol. 2002; 156: 11–22.

Clausen P, Nolet BA, Fox AD, Klaassen M. Long-distance endozoochorous dispersal of submerged macrophyte seeds by migratory waterbirds in northern Europe–a critical review of possibilities and limitations. Acta Oecol. 2002; 23: 191–203.

Figuerola J, Green AJ. How frequent is external transport of seeds and invertebrate eggs by waterbirds? A study in Doñana, SW Spain. Arch Hydrobiol. 2002; 155: 557–565.

Green AJ, Figuerola J, Sánchez MI. Implications of waterbird ecology for the dispersal of aquatic organisms. Acta Oecol. 2002; 23: 177–189.

Brochet A-L, Guillemain M, Fritz H, Gauthier-Clerc M, Green AJ. The role of migratory ducks in the long-distance dispersal of native plants and the spread of exotic plants in Europe. Ecography. 2009; 32: 919–928.

Brochet A-L, Guillemain M, Fritz H, Gauthier-Clerc M, Green AJ. Plant dispersal by teal (Anas crecca) in the Camargue: duck guts are more important than their feet. Freshwater Biol. 2010; 55: 1262–1273.

Kaplan Z, Šumberová K, Formanová I, Ducháček M. Re-establishment of an extinct population of the endangered aquatic plant Potamogeton coloratus. Aquat Bot. 2014; 119: 91–99.

Becker M, Gruenheit N, Steel M, Voelckel C, Deusch O, Heenan PB, McLenachan PA, Kardailsky O, Leigh JW, Lockhart PJ. Hybridization may facilitate in situ survival of endemic species through periods of climate change. Nat Clim Chang. 2013; 3: 1039–1043.

Rieseberg LH, Carney SE. Plant hybridization (Tansley Review No. 102). New Phytol. 1998; 140: 599–624. PubMed

Li XW, Yang Y, Henry RJ, Rossetto M, Wang YT, Chen SL. Plant DNA barcoding: from gene to genome. Biol Rev. 2015; 90: 157–166. doi: 10.1111/brv.12104 PubMed DOI

Fehrer J, Slavíková-Bayerová Š, Orange A. Large genetic divergence of new, morphologically similar species of sterile lichens from Europe (Lepraria, Stereocaulaceae, Ascomycota): concordance of DNA sequence data with secondary metabolites. Cladistics. 2008; 24: 443–458. PubMed

Fehrer J, Gemeinholzer B, Chrtek J Jr, Bräutigam S. Incongruent plastid and nuclear DNA phylogenies reveal ancient intergeneric hybridization in Pilosella hawkweeds (Hieracium, Cichorieae, Asteraceae). Mol Phylogen Evol. 2007; 42: 347–361. PubMed

Du ZY, Qimike A, Yang CF, Chen JM, Wang QF. Testing four barcoding markers for species identification of Potamogetonaceae. J Syst Evol. 2011; 49: 246–251.

Soltis DE, Mavrodiev EV, Doyle JJ, Rauscher J, Soltis PS. ITS and ETS sequence data and phylogeny reconstruction in allopolyploids and hybrids. Syst Bot. 2008; 33: 7–20.

Chrtek J Jr, Zahradníček J, Krak K, Fehrer J. Genome size in Hieracium subgenus Hieracium (Asteraceae) is strongly correlated with major phylogenetic groups. Ann Bot. 2009; 104: 161–178. doi: 10.1093/aob/mcp107 PubMed DOI PMC

Borsch T, Hernández-Ledesma P, Berendsohn WG, Flores-Olvera H, Ochoterena H, Zuloaga FO, von Mering S, Kilian N. An integrative and dynamic approach for monographing species-rich plant groups–building the global synthesis of the angiosperm order Caryophyllales. Perspect Pl Ecol Evol Syst. 2015; 17: 284–300.

Mace GM. The role of taxonomy in species conservation. Philos Trans R Soc B. 2004; 359: 711–719. PubMed PMC

Smith GF, Buys M, Walters M, Herbert D, Hamer M. Taxonomic research in South Africa: the state of the discipline. S Afr J Sci. 2008; 104: 254–256.

Kirschner J, Kaplan Z. Taxonomic monographs in relation to global Red Lists. Taxon. 2002; 51: 155–158.

Von Staden L, Raimondo D, Dayaram A. Taxonomic research priorities for the conservation of the South African flora. S Afr J Sci. 2013; 109: 1–10.

Kolář F, Kaplan Z, Suda J, Štech M. Populations of Knautia in ecologically distinct refugia on the Hercynian massif belong to two endemic species. Preslia. 2015; 87: 363–386.

Ennos RA, French GC, Hollingsworth PM. Conserving taxonomic complexity. Trends Ecol Evol. 2005; 20: 164–168. doi: 10.1016/j.tree.2005.01.012 PubMed DOI

Piett S, Hager HA, Gerrard C. Characteristics for evaluating the conservation value of species hybrids. Biodivers Conserv. 2015; 24: 1931–1955.

O’Brien SJ, Mayr E. Bureaucratic mischief: Recognizing endangered species and subspecies. Science. 1991; 251: 1187–1188. doi: 10.1126/science.251.4998.1187 PubMed DOI

vonHoldt BM, Cahill JA, Fan Z, Gronau I, Robinson J, Pollinger JP et al. Whole-genome sequence analysis shows that two endemic species of North American wolf are admixtures of the coyote and gray wolf. Science Advances. 2016; 2: e1501714. PubMed PMC

Evolutionary history and patterns of geographical variation, fertility, and hybridization in Stuckenia (Potamogetonaceae)

Molecular Evolution and Organization of Ribosomal DNA in the Hawkweed Tribe Hieraciinae (Cichorieae, Asteraceae)

The root-symbiotic Rhizoscyphus ericae aggregate and Hyaloscypha (Leotiomycetes) are congeneric: Phylogenetic and experimental evidence