About Names and Taxa

Sources of the Names

Names cited in this website originated as part of a "data dump" for the Violaceae family, provided to Harvey Ballard from the IPNI staff at the Royal Botanic Garden in Kew, London, England in 2004. New names published since then, as well as others that have come to light, have been added. All names were incorporated into a BRAHMS (Botanical Research and Herbarium Management System) database and then split into two databases, with one representing North America north of Mexico and the other, all other regions of the world. The International Plant Names Index (www.ipni.org, under the "Links" menu) provided internationally accepted abbreviations for taxonomic authorities and literature citations for publications of scientific names.

Accepted Names and Taxa

The Violaceae as named, circumscribed and characterized in two submitted regional treatments to be published or made available in the near future formed much of the basis for this website, although a great deal of additional research was necessary. One treatment, the Violaceae of northeastern North America, was prepared for Rob Naczi's "New Gleason and Cronquist" manual of the northeastern United States and Canada. The second treatment, assembled with Alan Weakley and Bruce Sorrie, will soon be posted as part of the newest version of Weakley's "Flora of the southeastern United States". Additional taxa occurring west to the Rocky Mountains and northwestward to the western Arctic have been added to complete the taxon coverage. Only those names established with confidence as the earliest available and validly published have been used as accepted names of taxa, and only names the identify of which has been established with little to no doubt (in most cases, by evaluating typifications) have been included as synonyms. Virtually all accepted names and all of the synonyms have been studied and typifications have been confirmed (see "Typifications" below). For some of the uncertain names, literature references with protologues have been obtained and type material has been identified but not critically studied; research on those will be accomplished in the near future.

Most accepted taxa discussed in this website are treated at the rank of species, including several undescribed species, as a consequence of our research approach (see "Species Concepts and Taxon Delineation in Violets" below, and "Integrative Taxonomy" in the "Our Research" dropdown menu). We also include information on several undescribed anomalous variants that belong to species complexes and do not appear (based on sparse evidence), to match any taxa we recognize. We are currently studying these, and we anticipate that with comprehensive evidence, some or all of these will prove to be worthy of recognition.

For each accepted taxon, I have provided hopefully relevant, useful comments concerning previous treatments of the taxon, interesting observations by violet specialists and authors of state or regional floras; identification or nomenclatural issues; distinctions from similar-looking taxa (although I assume the reader would consult the keys for diagnostic features in identifying violets); and other interesting observations of taxonomy, ecology, or geography. I have not attempted to consult checklists, atlases, "wildflower" guides, county-level florulas, or floras of municipal, state or national parks (although I will investigate literature on national parks in the region of concern in the near future). I have thus far consulted publications by Brainerd (1921b, 1924), Baird (1942), Fernald (1950), Henry (1953a), Russell (1955c), Jørgensen et al. (1958), Alexander (1963), Russell (1965), Lévesque and Dansereau (1966), Scoggan (1978), Strausbaugh and Core (1978), Swink and Wilhelm (1979), Ballard (1995, 2000, 2013), McKinney (1992), Gil-ad (1995, 1997, 1998), McKinney and Russell (2002), Haines et al. (2011), Voss and Reznicek (2012), Weakley et al. (2012), and Little and McKinney (2015). Additional literature will be consulted in the near future will include the work of Klaber (1976), Great Plains Flora Association (1986), Diggs et al. (1999), and several other state floras in our region published since Fernald's 1950 manual. I am relying on James Smith's (2019) valuable and comprehensive bibliography of North American floras, manuals and checklists as a guide to identify additional literature.

Species Concepts and Taxon Delineation in Violets

Species concepts have been under discussion, or in hot debate, for more than a century. Mishler and Donoghue (1982), Sluys (1991), Baum and Donoghue (1993, 1995), Luckow (1995), Olmstead (1995), Meeus et al. (2003), Aleixo (2007), Knapp (2008) and Haveman (2013) reviewed the two dozen-plus species concepts from theoretical and practical perspectives. Slobodchikoff (1976), Mishler and Donoghue (1982), Mishler (1985), Olmstead (1995), Zink and McKitrick (1995), Collar (1996), Wheeler and Meier (2000), Fraser and Bernatchez (2001), Pratt and Pratt (2001), Garnett and Christidis (2007), Vetter and Storch (2009), Rojas-Soto et al. (2010), Braby et al. (2012), and Frankham et al. (2012) examined the impacts of different taxon delineations and species concepts on biodiversity recognition and conservation. Mayden (1997), de Queiroz (2005, 2007), and Naomi (2011) reexamined theoretical and practical aspects of species concepts, with the aim of understanding the underpinnings common to all of them and devising a more fundamental and unified approach to species delimitation. The General Lineage or Unified Species Concept of de Queiroz in particular reflects the understanding of many taxonomists and biologists–that organisms on the landscape represent aggregates of populations comprising distinct evolutionary units one may call a species, with individuals within a species connected by realized or potential gene flow and an ancestry of common descent, and behaving through space and time in an interrelated pattern represented by metapopulation dynamics. de Queiroz proposed that the overarching theme common to all species concepts is a species as a separately evolving metapopulation. To "diagnose" or delineate a species, one must use various types of evidence, and former individual species concepts then become data sources from which one evaluates a set of populations to determine whether or not those populations meet the definition of a species. de Queiroz pointed out that each individual line of evidence will likely give a different viewpoint on how differentiated the set of populations under study is in comparison to its sister taxon (in a simple taxon-pair diverging from the most recent common ancestor), or from related sets of populations. de Queiroz noted that any line of evidence that provides support for a set of populations as a species under the Unified Species Concept is sufficient but argued that more and diverse evidence is better. It is worth noting that the unified species concept allows for any speciation mechanism to produce evolutionary species, including hybrid origin.

It has been customary until relatively recently that plant taxonomists (and violet specialists) did not explicitly state (or, perhaps, did perceive it necessary to state) which species concept(s) they were utilizing to detect, delineate and describe species. Generally, they (and we) have utilized the morphological species concept, at least in the initial approach to detect a set of plants or populations to examine further. Norman Russell (1953, 1955c, 1958a, 1958b, 1959, 1961, and 1965) relied largely on an implicit morphological species concept using predominately largely vegetative traits to delimit taxa. He also examined photoperiodic responses (Russell 1960), variation patterns in several violet species (1954b, 1955b, 1956b, 1956c, Russell and Graham 1958, and Russell and Crosswhite 1963), and hybridization events (1952, 1954a, 1955a, 1956a, Russell and Cooperrider 1955a, 1955b, Russell and Bowen 1960, Russell and Risser Jr. 1960) to delineate taxa, although he did not avail himself of other data such as relative reproductive fitness or isolation mechanisms. Landon McKinney (1977, 1992, McKinney and Blum 1978, 1981, McKinney and Russell 2002) used an implicit morphological species concept that was virtually exclusively confined to vegetative characteristics. Little and McKinney (2015) also employed an implicit morphological species concept but consulted additional evidence from the literature in determining the limits and ranks of many taxa. A few other specialists have taken steps beyond morphology, invoking other concepts to reassess initially morphologically defined taxa. Ezra Brainerd was the first to exploid morphological characteristics of reproductive structures and the behavior or hybrids as it related to the parental taxa. He reported extensively on observations of relative fertility (or sterility) of parental taxa and their hybrids, including any hybrid progeny through the F3 and F4 generations, documenting universal cessation of chasmogamous reproduction, sterility (with no viable seeds) of hybrids of all lineages in North America but the Boreali-Americanae, and sterility or reduced seed output in cleistogamous reproduction in de novo hybrids of the Boreali-Americanae. In cultivating nearly every North American violet in a common garden over a 20-plus year period, he also documented genetically fixed differences among taxa across the growing season and reported on patterns of natural variability in the taxa he recognized (Brainerd 1904a, 1904b, 1905, 1906a, 1906b, 1906c, 1907a, 1907b, 1909, 1910a, 1910b, 1911a, 1911b, 1911c, 1912, 1913a, 1913c, 1913d, 1917a, 1917b, 1921b, 1924). Thus, he implicitly employed a morphological species concept coupled with a modified biological species concept, with elements of a genealogical species concept. In their taxonomic scrutiny of western violets, in which polyploid evolution has been far more active than in eastern North American members, Milo Baker and Jens Clausen (Baker 1935, 1936, 1940, 1949a, 1949b, 1949c, 1953, 1957, Clausen 1964) and Garrett Davidse (1968, 1976) employed both morphological and genetic species concepts in detecting and delineating taxa and recognizing parentage of allopolyploid species. Fabijan et al. (1988) used morphology, biochemistry, morphometric analysis, and chromosome numbers (therefore applying a pluralistic approach involving morphological, biochemical, phenetic and genetic species concepts) to delineate taxa in the primarily western Nuttallianae group of caulescent yellow-flowered violets. In his dissertation research with the Acaulescent Blue violets of Viola subsect. Boreali-Americanae, Nir Gil-ad examined macromorphological features in a more exhaustive and explicit fashion than had ever been accomplished before (Gil-ad 1995, 1997, 1998). He utilized presumably conserved micromorphological features of lateral petal trichomes and seed coats way as a proxy for genetic evidence to delimit taxa and infer potential hybrids or hybrid derivatives. His working hypothesis was that all taxa could be hybrid derivatives, and he sought evidence to reject this hypothesis in a quest to identify and circumscribe orthospecies. He excluded all taxa interpreted as expressing intermediate or non-unique features as hybrids or hybrid derivatives, admitting that this would also exclude taxa now behaving as species that were potentially "stabilized" and of ancient hybrid origin, as well as de novo hybrids. He explicitly employed a modified phylogenetic diagnosability criterion (in the absence of population-level phylogenetic analysis), to which he added the further requirement that at least one unique reproductive feature and unique micromorphological features in lateral petal trichomes and/or seed coats must be present to consider a taxon an orthospecies. He was the first specialist to utilize a phylogenetic species concept (or, rather, a criterion) to evaluate and delineate taxa. Gil-ad provided the first comprehensive descriptions of accepted orthospecies and some of the first methodical and critical typifications for the Boreali-Americanae. Ballard (1985, 1987, 1990, 1995, 2000, 2013, Ballard and Gawler 1994, McCauley and Ballard 2013) adhered closely to Russell's (1965) taxonomic concepts and, early on, employed a morphological species concept alone in recognizing non-hybrid taxa. With hybrids, he alluded to observed reproductive behavior, including pollen stainability or capsule and seed production (Ballard 1990a, 1990b, 1993). He later added morphometric analysis of morphological and other data (Ballard and Wujek 1994, Ballard et al. 2001), relying heavily on the phenetic species concept. His thesis on Rostrate violets (Ballard 1992) included micromorphology of styles and leaf surfaces, morphometrics of macromorphological data, and analysis of flavonoid chromatographic results (a more pluralistic approach to taxon delineation).

Beginning in 2012, my students and I began employing a broader, integrative taxonomic approach with the unified species concept as the most expansive and objective evolutionary species concept for detecting and delineating species, infraspecific taxa and hybrids. In applying the unified species concept to violets as an operational "filter" on the empirical evidence we generated, a number of practical points became obvious. First, in order for a population or taxon under study to conform to a metapopulation, it must have the ability to create genetically and phenotypically similar progeny. This excludes sterile de novo hybrids from consideration, which are the only type of hybrid produced among species in the caulescent groups of our region and among the acaulescent whites (subsect. Stolonosae). Also excluded are de novo hybrids in the first several (or many?) hybrid generations in the taxonomically challenging stemless blues (subsect. Boreali-Americanae), because they do not reproduce by chasmogamous means, and cleistogamous capsules of the hybrids–when not fully sterile–produce recombinant progeny expressing different combinations of phenotypic traits underlain by different genotype combinations of the parental species. Thus, they do not conform to the expectations of a single species metapopulation. A species with a hybrid origin in the more distant past, that had become genetically and phenotypically stabilized, could conform to the unified species concept. Trivial population-level allelic forms, as well as minor regional variants, could potentially be shown to belong to a single separately evolving metapopulation through careful morphological analysis, observations of pollinator and reproductive behaviors, or other means, although genetic evidence would be ideal. In comparing sets of more divergent populations, examining within- and among-population variation in individual phenotypic traits and making comparisons of traits and their variation patterns in similar sets of populations would provide some evidence that one is dealing with a single distinct metapopulation, while evidence from ecological niche, phenology, and other non-genetic sources, perhaps aided by statistical tests, would provide additional evidence to delineate separately evolving (or differentiated) sets of populations. Genetic data (e.g., from microsatellite loci or another population-level multi-locus approach, and perhaps plastid markers) would provide important corroborative evidence to test for potential or realized gene flow representing coalescent relationships among populations of the study group, versus hybridization (whether recent or ancient). A flurry of contributed conference talks and posters have resulted from this new approach and species concept (Ballard 2016, 2017, 2018, 2019a, 2019b, Robertson and Ballard 2014, Zink and Ballard 2014, Zumwalde and Ballard 2014, Ballard et al. 2015, Benson and Ballard 2015, Greff and Ballard 2018, Hastings and Ballard 2018, Burwell and Ballard 2019, Chilson and Ballard 2019), as well as completed Masters theses (Zumwalde 2015, Hastings 2018). Several manuscripts are nearing completion for submission that present some of our data on newly detected undescribed species. A recent example in which an undescribed Palustres violet was detected initially from molecular phylogenetic data (namely, single-copy nuclear genes), and further delineated using morphological traits, was published by Blaxland et al. (2018). In our studies, we have found that detailed morphological analysis, ecological characterization, and examination of reproductive behavior and hybrids with other taxa are minimally sufficient to confidently detect and delineate uniform sets of populations as species under the unified species concept. Sets of living plants from several to many populations over the range of a taxon under study, grown in a common garden, are critical to determining genetically fixed differences among similar sets of populations, especially during different parts of the growing season (chasmogamous flower and cleistogamous fruit in particular). Following Gil-ad's approach, we scrutinize and record quantitative and qualitative macromorphological traits across the plant body and micromorphological features of lateral petal trichomes and seed coats; analyze site and soil variables to characterize the ecological niche; record mature seed vs. abortive ovule number and image seeds from formerly bagged cleistogamous capsules after natural dehiscence to document reproductive behavior in the putative species and in any hybrids with other taxa. In certain instances we find funds to generate molecular marker data to evaluate the extent of genetic differentiation (recently we have employed microsatellite loci identified using shotgun genome sequencing, but we are now exploring double-digest genotying-by-sequencing). We delineate taxa as narrowly as the evidence drives us to do. We place no requirements on the number or type of characteristics or evidence required to support a set of populations as a distinct evolutionary species, nor do we establish preconceived notions on how subtle or dramatic are the suite of characteristics that delineate an evolutionary species from others. Instead, we let the plants and their evolutionary histories speak for themselves. As a consequence, more taxa have been found to represent distinct evolutionary species than previously known, and (perhaps not surprisingly) very few infraspecific taxa have been recognized; the few have generally been morphologically distinctive taxa that are clearly within the genetic structure of a broader species but that possess an unusual ecological or geographic component that urges recognition.

Typifications

Hundreds of names have been published for the native violets occurring in the Great Plains and eastern North America. As McNeill (2014) notes, designation of a holotype as a requirement for valid publication of a plant name has only been in force since 1990. Names published prior to that may or may not have cited specimens which could be construed as holotypes or any type material. For many names of violets published in the middle of the last century or before, authors often dispensed with citing any particular specimens, and when they did cite specimens they commonly listed multiple collections, and they commonly failed to note which herbarium harbored them. Nevertheless, it is incumbent on the specialist to attempt to typify each name. Some of the most widely used names (including accepted names) have been typified, some by McKinney and many by Gil-ad. However, many names have received no attention, and under the current code some typified names need further typification or re-typification (especially where "holotype" was assumed but could not be undeniably proven). McNeill cautions against lax interpretations of type material as representative of holotypes and points out that the requirements for a satisfactory holotype designation by the author of a name are more stringent than have usually been applied in past typifications. In reviewing the 100-plus names of North American violets published by E. L. Greene as well as the names most commonly applied to or accepted for violets in our region, almost none of them are supported by holotypes as specified by the current International Code of Nomenclature for Algae, Fungi and Plants (Turland et al. 2018). Most names require at least lectotypification (assuming original material can be found), and some may require neotypification. For the moment, types are cited mostly for accepted names where they are known or suspected. Clarifying comments are given in brackets.

Literature Cited

Aleixo, A. 2007. Species concepts and the ever lasting conflict between continuity and operationality: a proposal of guidelines for assigning species rank by the Brazilian Check-list Committee. Revista Brasileira de Ornitologia 15: 297–310.
Alexander, E. J. 1963. Violaceae. In Gleason, H. A., The new Britton and Brown illustrated flora of the northeastern United States and adjacent Canada. Hafner Publishing Co., Inc., New York, NY. 552-567.
Baker, M. S. 1935. Studies in western violets-I. Sections Chamaemelanium and Nomimium. Madroño 3: 51–57.
Baker, M. S. 1936. Studies in western violets-II. New species and varieties. Madroño 3: 232–239.
Baker, M. S. 1940. Studies in western violets-III. Madroño 5: 218–231.
Baker, M. S. 1949a. Studies in western violets, VI. Madroño 10: 110–128.
Baker, M. S. 1949b. Studies in western violets-IV. Leaflets of Western Botany 5: 141–147.
Baker, M. S. 1949c. Studies in western violets-V. Leaflets of Western Botany 5: 173–177.
Baker, M. S. 1953. Studies in western violets, VII. Madroño 12: 8–18.
Baker, M. S. 1957. Studies in western violets-VIII. The Nuttalianae [sic!] continued. Brittonia 9: 217–230.
Ballard Jr., H. E. 1985. Viola epipsila new to Michigan and the eastern United States. Michigan Botanist 24: 131–134.
Ballard Jr., H. E. 1987. Violaceae. Argus, G. and K. Pryer (eds.).  Atlas of Ontario rare plants, [10]. National Museum of Natural Sciences, Ottawa, Canada.
Ballard Jr., H. E. 1990a. Hybrids among three caulescent violets, with special reference to Michigan. Michigan Botanist 29: 43–54.
Ballard Jr., H. E. 1990b ['1989']. Viola ×eclipes, a new hybrid violet. Michigan Botanist 28: 216–219.
Ballard Jr., H. E. 1992. Systematics of Viola section Viola in North America north of Mexico. M.S. thesis. Central Michigan University, Mount Pleasant, MI.
Ballard Jr., H. E. 1993. Three new rostrate violet hybrids from Appalachia. Castanea 58: 1–9.
Ballard Jr., H. E. 1995 ["1994"]. Violets of Michigan. Michigan Botanist 33: 131-199.
Ballard Jr., H. E. 2000. Violaceae. In Rhoads, A. (ed.). Flora of Pennsylvania. University of Pennsylvania Press, Philadelphia, PA. 700-710.
Ballard Jr., H. E. 2013. Violaceae. In Yatskievych, G., Flora of Missouri. Missouri Botanical Garden Press, St. Louis, MO. 1218-1243.
Ballard Jr., H. E. 2016. Reinventing taxonomy for the Acaulescent Blue violets (Viola subsect. Boreali-Americanae), or there are a lot more species out there than we thought. XConference presentation, Association of Southeastern Biologists/Southern Appalachian Botanical Society, Concord, NC.
Ballard Jr., H. E. 2017. Integrative systematic studies drive a taxonomic revolution in the violet family (Violaceae). Invited talk, Carnegie Museum, Pittsburgh, PA.
Ballard Jr., H. E. 2018. Integrative taxonomic studies of the Salad Violet (Viola edulis) species group. Conference presentation, Botany 2018, Rochester, MN.
Ballard Jr., H. E. 2019a. Delineating evolutionary species & defining species groups in the Acaulescent Blue violets (Viola subsect. Boreali-Americanae). Conference presentation, Botany 2019, Tucson, AZ.
Ballard Jr., H. E. 2019b. The status of violet (Violaceae) taxonomy in the southeastern U.S. flora. Conference presentation, Association of Southeastern Biologists/Southern Appalachian Botanical Society, Memphis, TN.
Ballard Jr., H. E., D. A. Casamatta, M. M. Hall, R. A. McCauley, M. C. Segovia-Salcedo, and R. G. Verb. 2001. Phenetic analysis shows conspecificity between Hispaniolan Viola domingensis Urban and North American Viola macloskeyi sensu lato (Violaceae). Brittonia 53: 122–136.
Ballard Jr., H. E., and S. C. Gawler. 1994. Distribution, habitat and conservation of Viola novae-angliae. Michigan Botanist 33: 35–52.
Ballard Jr., H. E., and D. E. Wujek. 1994. Evidence for the recognition of Viola appalachiensis. Systematic Botany 19: 523–538.
Ballard Jr., H. E., B. Zumwalde, B. Gahagen, T. Roth. 2015. Are we missing species diversity in the acaulescent blue violets? Conference presentation, Botany 2015, Edmonton, Alberta.
Baum, D., and M. Donoghue. 1993. Choosing among alternative phylogenetic species concepts. American Journal of Botany 80: 115.
Baum, D. A., and K. L. Shaw. 1995. Genealogical perspectives on the species problem. Experimental and molecular approaches to plant biosystematics, Hoch, P. C. and A. G. Stephenson (eds.), 289–303. Missouri Botanical Garden Press, St. Louis, MO.
Benson, C., and H. E. Ballard, Jr. Botany 2015. Studies on the perplexingly variable Viola subsinuata complex (Violaceae). Conference presentation, Botany 2015, Edmonton, Alberta.
Blaxland, K., H. E. Ballard, and T. Marcussen. 2018. Viola pluviae sp. nov. (Violaceae), a member of subsect. Stolonosae in the Pacific Northwest region of North America. Nordic Journal of Botany 36.
Braby, M. F. 2010. The merging of taxonomy and conservation biology: a synthesis of Australian butterfly systematics (Lepidoptera: Hesperioidea and Papilionoidea) for the 21(st) century. Zootaxa: 13–76.
Brainerd, E. 1904a. Hybridism in the genus Viola. Rhodora 6: 213–223.
Brainerd, E. 1904b. Notes on New England violets. Rhodora 6: 8–17.
Brainerd, E. 1905. Notes on New England violets,-II. Rhodora 7: 1–8, Plate 50.
Brainerd, E. 1906a. How stems and stolons disappear in Viola. Bulletin of the Vermont Botanical Club 1: 11.
Brainerd, E. 1906b. Hybridism in the genus Viola,-II. Rhodora 8: 6–10.
Brainerd, E. 1906c. Hybridism in the genus Viola,-III. Rhodora 8: 49–61, Plates 66-70.
Brainerd, E. 1907a. Mendel’s law of dominance in the hybrids of Viola. Rhodora 9: 211–216.
Brainerd, E. 1907b. The behavior of seedlings of certain violet hybrids. Science 25: 940–944.
Brainerd, E. 1909. Another hybrid between a white and a blue violet. Rhodora 11: 115–116.
Brainerd, E. 1910a. Five new species of Viola from the south. Bulletin of the Torrey Botanical Club 37: 523–528, Plates 34, 35.
Brainerd, E. 1910b. The evolution of new forms in Viola through hybridism. American Naturalist 44: 229–236.
Brainerd, E. 1911a. Further notes on the stemless violets of the south. Bulletin of the Torrey Botanical Club 38: 1–9.
Brainerd, E. 1911b. The caulescent violets of the southeastern United States. Bulletin of the Torrey Botanical Club 38: 191–198.
Brainerd, E. 1911c. Viola palmata and its allies. Bulletin of the Torrey Botanical Club 37: 581–590, plate 36.
Brainerd, E. 1912. Violet hybrids between species of the palmata group. Bulletin of the Torrey Botanical Club 39: 85–97.
Brainerd, E. 1913a. Four hybrids of Viola pedatifida. Bulletin of the Torrey Botanical Club 40: 249–260.
Brainerd, E. 1913c. Notes on new or rare violets of northeastern America. Rhodora 15: 112–115.
Brainerd, E. 1921b. Violets of North America. Vermont Agricultural Experiment Station Bulletin 224: 1–172.
Brainerd, E. 1924. Some natural violet hybrids of North America. Vermont Agricultural Experiment Station Bulletin 239: 1–205.
Brainerd Baird, V. 1942. Wild violets of North America. University of California Press, Berkeley, CA.
Burwell, R., and H. E. Ballard. 2019. Preliminary integrative taxonomic investigations on the Affinis and Edulis species groups of Coastal Plain violets (Viola). Conference poster, Botany 2019, Tucson, AZ.
Chilson, N., and H. E. Ballard. 2019. Three from one: A taxonomic study of the Threepart Violet (Viola tripartita). Conference poster, Botany 2019, Tucson, AZ.
Clausen, J. 1964. Cytotaxonomy and distributional ecology of western North American violets. Madroño 17: 173–204.
Collar, N. J. 1996. Species concepts and conservation: A response to Hazevoet. Bird Conservation International 6: 197–200.
Davidse, G. 1968. A biosystematic investigation of the intermountain yellow violets. M.S. thesis. Utah State University, Logan, UT.
Davidse, G. 1976. A study of some intermountain violets (Viola sect. Chamaemelanium). Madroño 23: 274–283.
Diggs, G. M., B. L. Lipscomb, and R. J. O'Kennon. 1999. Shinners' and Mahler's illustrated flora of North Central Texas. Botanical Research Institute of Texas, Fort Worth, TX. 1060-1064.
Fabijan, D. M., J. G. Packer, and K. E. Denford. 1988. The taxonomy of the Viola nuttallii complex. Canadian Journal of Botany 65: 2562–2580.
Fernald, M. L. 1950. Violaceae. In Gray’s Manual of Botany, 8th ed. American Book Company, New York, NY. 1022-1042.
Frankham, R., J. D. Ballou, M. R. Dudash, M. D. B. Eldridge, C. B. Fenster, R. C. Lacy, J. R. Mendelson, et al. 2012. Implications of different species concepts for conserving biodiversity. Biological Conservation 153: 25–31.
Fraser, D. J., and L. Bernatchez. 2001. Adaptive evolutionary conservation: Towards a unified concept for defining conservation units. Molecular ecology 10: 2741–2752.
Garnett, S. T., and L. Christidis. 2007. Implications of changing species definitions for conservation purposes. Bird Conservation International 17: 187–195.
Gil-ad, N. L. 1995. Systematics and evolution of Viola L. subsection Boreali-Americanae (W. Becker) Brizicky. Ph.D. dissertation. University of Michigan, Ann Arbor, MI.
Gil-ad, N. L. 1997. Systematics of Viola subsection Boreali-Americanae. Boissiera 53: 1-130.
Gil-ad, N. L. 1998. The micromorphologies of seed coats and petal trichomes of the taxa of Viola subsect. Boreali-Americanae (Violaceae) and their utility in discerning orthospecies from hybrids. Brittonia 50: 91-121.
Gleason, H. A., and A. Cronquist. 1991. Violaceae. In Manual of vascular plants of northeastern United States and adjacent Canada, 2nd ed. New York Botanical Garden, Bronx, NY. 157-163.
Great Plains Flora Association. 1986. Violaceae. In Flora of the Great Plains. University Press of Kansas, Lawrence, KS. 1392 pp.
Greff, A., and H. E. Ballard, Jr. 2018. Integrative taxonomic studies of the Viola edulis complex. Conference poster, Association of Southeastern Biologists/Southern Appalachian Botanical Society, Myrtle Beach, SC.
Haines, A., E. Farnsworth, and G. Morrison. 2011. Violaceae. In Flora Novae Angliae. Yale University Press, New Haven, CT. 873-886.
Hastings, J. L. 2018. Systematic and ecological studies of the Viola subsinuata species complex. MS thesis, Ohio University, Athens, OH.
Hastings, J., and H. E. Ballard, Jr. 2018. Niche separation of Virginia populations of the Viola subsinuata complex supports recognition of four morphospecies. Conference presentation, Association of Southeastern Biologists/Southern Appalachian Botanical Society, Myrtle Beach, SC.
Haveman, R. 2013. Freakish patterns - species and species concepts in apomicts. Nordic Journal of Botany 31: 257–269.
Henry, L. K. 1953a. The Violaceae in western Pennsylvania. Castanea 18(2): 37-59.
Jørgensen, C. A., T. Sørensen, and M. Westergaard. 1958. The flowering plants of Greenland–A taxonomical and cytological survey. Biol. Skr. 9(4): 1-172. Klaber, D. 1976. Violets of the United States. A. S. Barnes & Company, Inc., South Brunswick, NJ.
Knapp, S. 2008. Species concepts and floras: what are species for? Biological Journal of the Linnean Society 95: 17–25.
Lévesque, L., and P. Dansereau. 1966. Études sur les violettes jaunes caulescentes de l’Est de l’Amerique du Nord. I. Taxonomic, nomenclature, synonymie et bibliographie. Naturaliste Canadien (Quebec) 93: 489-569.
Little, R. J., and L. E. McKinney. 2015. Violaceae. Flora of North America: Cucurbitaceae to Droseraceae, 106. Oxford University Press, New York, NY.
Luckow, M. 1995. Species concepts: Assumptions, methods, and applications. Systematic Botany 20: 589–605.
Mayden, R. L. 1997. A hierarchy of species concepts: the denouement in the saga of the species problem. Species: The Units of Biodiversity, Claridge, M. F., H. A. Dawah, and M. R. Wilson (eds.), 381–424. Chapman & Hall, London, England.
McCauley, R. A., and H. E. Ballard Jr. 2013. Viola calcicola (Violaceae), a new endemic violet from the Guadalupe Mountains of New Mexico and Texas. Journal of the Botanical Research Institute of Texas 7: 9–20.
McKinney, L. E. 1977. Preliminary studies of the acaulescent blue violets (Viola) with special reference to middle Tennessee. M.S. thesis. Middle Tennessee State University, Murfreesboro, TN.
McKinney, L. E. 1992. A taxonomic revision of the acaulescent blue violets (Viola) of North America. Sida, Botanical Miscellany 7: 1–60.
McKinney, L. E., and K. E. Blum. 1978. Leaf variation in five species of acaulescent blue violets (Viola. I. Castanea 43: 95–107.
McKinney, L. E., and K. E. Blum. 1981. A preliminary study of a polyspecies complex in Viola. Castanea 46: 281–290.
McKinney, L. E., and N. H. Russell. 2002. Violaceae of the southeastern United States. Castanea 67: 369–379.
McNeill, J. 2014. Holotype specimens and type citations: General issues. Taxon 63(5): 1112-1113.
de Meeus, T., P. Durand, and F. Renaud. 2003. Species concepts: What for? Trends in parasitology 19: 425–427.
Mishler, B. D. 1985. The morphological, developmental, and phylogenetic basis of species concepts in bryophytes. Bryologist 88: 207–214.
Mishler, B. D., and M. J. Donoghue. 1982. Species concepts: A case for pluralism. Systematic Zoology 31: 491–503.
Naomi, S.-I. 2011. On the integrated frameworks of species concepts: Mayden’s hierarchy of species concepts and de Queiroz’s unified concept of species. Journal of Zoological Systematics and Evolutionary Research 49: 177–184.
Olmstead, R. 1995. Species Concepts and Plesiomorphic Species. Systematic Botany 20: 623–630.
Pratt, H. D., and T. K. Pratt. 2001. The interplay of species concepts, taxonomy, and conservation: Lessons from the Hawaiian avifauna. Studies in Avian Biology: 68–80.
de Queiroz, K. 2005. A unified concept of species and its consequences for the future of taxonomy. Proceedings of the California Academy of Sciences 56: 196–215.
de Queiroz, K. 2007. Species concepts and species delimitation. Systematic Biology 56: 879–886.
Robertson, A., and H. E. Ballard, Jr. 2014. Do cryptic species partly explain extensive variation in eastern North American Viola subsinuata (Violaceae)? Conference poster, Botany 2014, Boise, ID.
Rojas-Soto, O. R., A. C. Navarro-Sigueenza, and A. E. D. L. Monteros. 2010. Systematics and bird conservation policies: the importance of species limits. Bird Conservation International 20: 176–185.
Russell, N. H. 1952. An example of introgressive hybridization between Viola papilionacea Pursh and V. nephrophylla. Proceedings of the Iowa Academy of Science 59: 134–140.
Russell, N. H. 1953. A resurvey of the violets of Iowa. Proceedings of the Iowa Academy of Science 60: 217–227.
Russell, N. H. 1954a. Three field studies of hybridization in the stemless white violets. American Journal of Botany 41: 679–686.
Russell, N. H. 1954b. Variation in leaf pubescence in Viola incognita Brainerd and V. renifolia Gray. Proceedings of the Iowa Academy of Science 61: 151–160.
Russell, N. H. 1955a. Local introgression between Viola cucullata Ait. and V. septentrionalis Greene. Evolution 9: 436–440.
Russell, N. H. 1955b. Morphological variation in Viola rotundifolia Michx. Castanea 20: 144–153.
Russell, N. H. 1955c. The taxonomy of the acaulescent white violets. American Midland Naturalist 54: 481–494.
Russell, N. H. 1956a. Hybridization between Viola pedatifida and its relatives. Castanea 21: 133–140.
Russell, N. H. 1956b. Morphological variation in Viola selkirkii Pursh. Castanea 21: 53–62.
Russell, N. H. 1956c. Regional variation patterns in the stemless white violets. American Midland Naturalist 56: 491–503.
Russell, N. H. 1958a. The nature of Viola missouriensis. Proceedings of the Iowa Academy of Science 65: 96–101.
Russell, N. H. 1958b. The violets of Tennessee 1. Keys to the species and distribution maps. Castanea 23: 63–76.
Russell, N. H. 1959. The violets of Minnesota. Proceedings of the Minnesota Academy of Science 25/26: 126–191.
Russell, N. H. 1960. Studies in the photoperiodic responses of violets (Viola). Southwestern Naturalist 5: 177–186.
Russell, N. H. 1961. Keys to Louisiana violets (Viola-Violaceae). Southwestern Naturalist 6: 184–186.
Russell, N. H. 1965. Violets (Viola) of the central and eastern United States: An introductory survey. Sida 1: 1–113.
Russell, N. H., and W. Bowen. 1960. A hypothesis to account for unusual leaf variation in Viola pedata L. Proceedings of the Iowa Academy of Science 67: 189-194.
Russell, N. H., and M. Cooperrider. 1955. Prediction of an introgressant in Viola. American Midland Naturalist 54: 42–51.
Russell, N. H., and F. S. Crosswhite. 1963. An analysis of variation in Viola nephrophylla. Madroño 17: 56–65.
Russell, N. H., and J. Graham. 1958. Midwestern population studies of Viola papilionacea Pursh. Proceedings of the Iowa Academy of Science 65: 102–109.
Russell, N. H., and A. C. Risser Jr. 1960. The hybrid nature of Viola emarginata. Brittonia 12: 298–305.
Scoggan, H. J. 1978. Violaceae. In Flora of Canada, Part 3–Dicotyledoneae (Saururaceae to Violaceae). National Museums of Canada. Ottawa, Canada. 1103-1115.
Slobodchikoff, C. N. 1976. Concepts of species. Dowden, Hutchinson & Ross; distributed by Halsted Press, Stroudsburg, Pa.; New York.
Sluys, R. 1991. Species Concepts Process Analysis and the Hierarchy of Nature. Experientia (Basel) 47: 1162–1170.
Smith Jr., J. P. 2019. North American floras, manuals, & checklists: A bibliography, 18th ed. Humboldt State University, Arcata, CA. [https://digitalcommons.humboldt.edu/botany_jps/4/] Strausbaugh, P. D., and E. L. Core. 1978. Violaceae. In Flora of West Virginia, 2nd ed. Seneca Books, Inc., Morgantown, WV. 644-658.
Swink, F., and G. Wilhelm. 1979. Violaceae. In Plants of the Chicago region, 2nd ed. revised and expanded. Morton Arboretum, Lisle, IL. 384, 801-810.
Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen, P. S., Knapp, S., Kusber, W.-H., Li, D.-Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (eds.) 2018: International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) adopted by the Nineteenth International Botanical Congress Shenzhen, China, July 2017. Regnum Vegetabile 159. Koeltz Botanical Books, Glashütten, Germany.
Vetter, D., and I. Storch. 2009. Umbrella Species: Effective Conservation Tool or Theoretical Construct? Validity of the concept and selection criteria using the example of birds. Naturschutz und Landschaftsplanung 41: 341–347.
Voss, E. G., and A. A. Reznicek. 2012. Violaceae. In Field manual of Michigan flora. The University of Michigan Press, Ann Arbor, MI. 913-922.
Weakley, A. S., J. C. Ludwig, and J. F. Townsend. 2012. Violaceae. In Flora of Virginia. BRIT Press, Fort Worth, TX. 963-975.
Wheeler, Q., and R. Meier. 2000. Species concepts and phylogenetic theory : a debate. Columbia University Press, New York.
Zink, J., and H. E. Ballard, Jr. 2014. Viola nephrophylla Greene in the eastern United States–new distributional records and habitat associations for an overlooked violet. Conference poster, Botany 2014, Boise, ID.
Zink, R. M., and M. C. McKitrick. 1995. The debate over species concepts and its implications for ornithology. Auk 112(3): 701-719.
Zumwalde, B. A. 2015. A systematic revision of the Viola pedatifida group and evidence for the recognition of Viola virginiana, a new narrow endemic of the Virginia Shale Barrens. MS thesis, Ohio University, Athens, OH.
Zumwalde, B. A., and H. E. Ballard, Jr. 2014. Preliminary Analysis of the Viola pedatifida Group and Evidence for a New Endemic Species. Conference poster, Botany 2014, Boise, ID.

 

Authored by Harvey Ballard on 14 March, 2020; last updated on 14 May, 2020.