Genomic Size and Ploidy Level Patterns of Intermountain West Lepidium Determined Using Flow Cytometry

Western North American Naturalist

Volume 74 Number 4 Article 1

3-30-2015

Genomic size and ploidy level patterns of Intermountain West Lepidium determined using flow cytometry

Robert W. Lichvar U.S. Army Engineer Research and Development Center, Hanover, NH, [email protected]

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Recommended Citation Lichvar, Robert W. (2015) "Genomic size and ploidy level patterns of Intermountain West Lepidium determined using flow cytometry," Western North American Naturalist: Vol. 74 : No. 4 , Article 1. Available at: https://scholarsarchive.byu.edu/wnan/vol74/iss4/1

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GENOMIC SIZE AND PLOIDY LEVEL PATTERNS OF INTERMOUNTAIN WEST LEPIDIUM DETERMINED USING FLOW CYTOMETRY

Robert W. Lichvar1

ABSTRACT.—The taxonomic status of members of the genus Lepidium in the Intermountain West has been in flux for years. Species concepts and classification of these endemic species from the western United States center on the highly variable L. montanum complex. Until recently, classification treatments that use morphological features in this group have been adequate, but as new species are discovered and more locations reported, the limited number of morphological features available for classification and defining species concepts has led to more uncertainty about taxonomic rankings. As part of a molecular and morphological-based treatment of the group, flow cytometry was used to evaluate 58 collections of Lepidium from the Intermountain West. The ploidy level for 14 species and 11 varieties of Lepidium was surveyed to assess whether ploidy levels affected the interpretation of taxonomic rankings. Of the Lepidium taxa surveyed, 90% were tetraploid, and several were diploid and hexaploid. Tetraploid occurrences crossed all major species and varieties. No geographic distribution or habitat patterns were associated with ploidy level.

RESUMEN.—Durante años, el estado taxonómico de los miembros del género Lepidium en el área intermontañosa del oeste ha estado en constante cambio. Los conceptos de especie y la clasificación de estas especies endémicas del oeste de los Estados Unidos se enfocan en el complejo L. montanum sumamente variable. Hasta hace poco, los trata- mientos de clasificación que utilizan características morfológicas en este grupo han sido adecuados, pero a medida que se descubren nuevas especies y se registran más ubicaciones, el limitado número de características morfológicas dispo- nibles para la clasificación y la definición de los conceptos de especie ha dado lugar a una mayor incertidumbre sobre las clasificaciones taxonómicas. Como parte de una técnica molecular y morfológica del grupo, se utilizó citometría de flujo para evaluar 58 colecciones de Lepidium en el área intermontañosa del oeste. Se realizó un estudio de ploidía en 14 especies y 11 variedades de Lepidium para evaluar si los niveles de ploidía afectaban la interpretación de las clasificaciones taxonómicas. El 90% de los Lepidium estudiados resultaron ser tetraploides, junto con varios taxa que son diploides y hexaploides. Las ocurrencias tetraploides cruzaron las principales especies y variedades. No se encontraron patrones de distribución o de hábitats geográficos asociados con el nivel de ploidía.

The Brassicaceae are distributed worldwide occurrence of hybridization, apomixis, and varia- and consist of 49 tribes, 321 genera, and more tion in ploidy levels; therefore, chromosome than 3660 species (Al-Shehbaz 2012). The use counts may or may not be supportive for taxo- of chromosome numbers for distinguishing nomic purposes. differences between genera in the Brassi- Base chromosome numbers in the family caceae has been limited (Rollins 1993). Even vary from x = 4 to x = 17, with more than though chromosome numbers are not taxo- one-third of the taxa having karyotypes of x = 8 nomically definitive in Brassicaeae, in some (Warwick and Al-Shehbaz 2006). Chromosome cases the numbers are consistent and not ran- counts reported by Warwick and Al-Shehbaz dom among different species groups. Rollins (2006) represent 232 of the 321 genera and (1955, 1979, 1993) showed that certain species 1558 of the 3660 species in Brassicaceae. Of groups within select genera share a similar base the species reported, approximately 37% are number and, in some cases, are associated with assumed to be polyploids. The percentage groups with specific morphological characteris- estimates may be even higher if diploid species tics. As such, chromosome numbers have sup- are shown to be paleopolyploids that formed ported taxonomic treatments in Brassicaceae from diploidization (Lysak et al. 2005). Frequent between some species (Rollins 1963, Mulligan auto- and alloploid events complicate the utility 1976) but have not been useful in other treat- of chromosome numbers even further, along ments (Mulligan 1966). As a whole, chromo- with chromosome reshuffling, fusions, and fis- some counts across the family express frequent sions, which have caused intrageneric numeric

1U.S. Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755. E-mail: [email protected]

369 370 WESTERN NORTH AMERICAN NATURALIST [Volume 74 variation and descending or ascending dys- from genome size can be used to indicate ploidy (Lysak et al. 2005). Thus, it is impractical the contributions of different parental origins to use the base number for taxonomic inter- (Wendel et al. 2002, Kellogg and Bennetzen pretation in some genera. In the Brassicaceae, 2004, Leitch and Bennett 2004). x = 4 is the lowest base number and is found As part of a taxonomic evaluation of native in 2 unrelated genera—Stenopetalum R. Brown species of Lepidium from the Intermountain from Australia and Physaria (Nutt.) A. Gray. West of the United States, a series of research The highest base number is x = 128, found in efforts has been undertaken. Recent taxonomic Cardamine (Easterly 1963, Al-Shehbaz 1988). treatments mention that this group needs fur- In Lepidium L., the base number is reported ther molecular studies to clarify species con- as x = 8, based on 231 counts from 60 species cepts and taxonomic rankings used in the (Warwick and Al-Shehbaz 2006). In the re- group (Holmgren 2005, Al-Shehbaz and Gaskin ported counts for Lepidium, 34% were diploid, 2010). As part of those efforts, this survey re - 14% both diploid and polyploid, and 52% ports on ploidy-level studies using flow cytom- entirely polyploid. Ploidy numbers in the genus etry methods. The morphological differences are reported as 2n = 16, 24, 28, 32, 40, 48, 64, that distinguish species and infraspecific taxa and 80. within this geographic region are faint but In addition to chromosome counts for sup- consistent within taxa, implying possible poly- porting the evaluation of ploidy levels, the ploidy, reticulate evolution, or recent hybrid amount of DNA per nucleus can now be origins. These differences have led to uncer- determined using techniques such as flow tainty about the taxonomic arrangement of the cytometry (FC; Bennett and Leitch 2005, group under review, particularly about what Doležel and Bartoš 2005). The species of Bras- constitutes the species level and how these sicaceae analyzed with FC to date have shown taxa are related to each other (Hitchcock 1936, small nuclear DNA contents and a narrow 1950, Rollins 1993, Holmgren 2005, Al-Shehbaz range of variation (Bennett and Leitch 2005). and Gaskin 2010). Genome size can now be superimposed over I used ploidy-level information derived from gene marker–based phylogenies for assessing flow cytometry methods to evaluate whether ancestral DNA content, and FC has provided ploidy-level patterns are helpful in revealing the ability to trace genome size evolution a taxonomic interpretation of Intermountain (Marhold and Lihová 2006). Likewise, DNA West Lepidium. One aspect I evaluated was content in polyploids of recent origin is ex- whether ploidy-level patterns are found along pected to be proportional to the ploidy level for geographic ranges associated with landscape the purposes of assessing ploidy level (Bennett or distribution patterns as reported in the et al. 2000). This pattern is reported in several literature (Suda et al. 2007, Whittemore and species of Draba L., which include diploids, Olson 2011). In this study, 2 main questions triploids, tetraploids, hexaploids, and up to 16- addressed the classification of western Lepid- ploids. This evidence is also supported by ium: (1) whether ploidy-level occurrences are molecular markers (Grundt et al. 2005, Jordon- associated with geologic, geographic, or eco- Thaden and Koch 2008). logical settings in the taxonomically problematic Polyploidization and hybridization often Lepidium and (2) whether ploidy levels are result in a reticulate pattern of evolution associated with certain species groups or cer- (Marhold and Lihová 2006). These events make tain infraspecific taxa within a species. reconstruction of evolutionary relationships challenging. Reticulate evolution can be de - METHODS tected by incongruences between phylogenetic Plant Material trees derived from plastidic (cp) and nuclear (nr) DNA. These incongruences are common Seeds were collected in the field, and plants in Lepidium between cpDNA and nrDNA ITS were grown in a greenhouse to provide green (internal transcribed spacers) markers, with leaf tissue for flow cytometry (FC; Table 1). common polyploids suggesting allopolyploid Seeds were obtained during several extensive speciation in the genus (Mummenhoff et al. field trips throughout the Intermountain West 2001, 2004). It has been suggested that increases between 2007 and 2009. Search locations of or decreases in ploidy levels as determined Lepidium of interest were developed using 2014] GENOMIC SIZE, PLOIDY LEVELS OF LEPIDIUM 371 location data from herbarium specimens at the Flow cytometry (FC) was performed on a Gray Herbarium (GH), the New York Botani- BD Bioscience FACSAria flow cytometer (BD cal Gardens Virtual Herbarium (Thiers, con- Bioscience, San Jose, CA) equipped with tinuously updated), and the Calflora (2008) FACSDiva Software (BD Bioscience, San Jose, herbaria databases online. Other voucher col- CA). Samples were run until 10,000 nuclei lections, including seeds, were collected by were scored. The DNA content was calculated several botanists and shipped to the Univer- by comparing the mean peak fluorescence sity of Alaska–Fairbanks (UAF; Table 1). with the internal reference standard, Glycine Seeds were collected from 3–5 individuals max (L.) Merr. ‘Polanka’ (2C = 2.5 pg DNA; per population. Leaf materials were collected Doležel and Bartoš 2005). Following Doležel from the same individuals for DNA extraction, and Bartoš (2005), the 2C value of each sam- and voucher specimens were collected from ple (somatic cell nuclear content) was esti- the population for morphological analysis and mated as the (sample peak mean/standard peak taxonomic identification. mean) × standard 2C DNA content (2.5 pg Geographic patterns of western Lepidium DNA). To verify the range of DNA content, were evaluated by developing distribution maps C values were compared to values reported in of data collection points using a geographic the Kew Royal Botanical Gardens DNA C- information system (GIS). Geographic Univer- values database (Bennett and Leitch 2012). sal Transverse Mercator (UTM) coordinates The 2C values were used to determine diploids were assigned to all Lepidium voucher speci- and tetraploids by comparison to reported mens and displayed as point locations in ArcGIS polyploidy levels from published chromosome 10.0. Based on the species localities, a distribu- counts (Warwick and Al-Shehbaz 2006). tion map was then created and digitized. Due to uncertainty of the taxonomic status Ploidy Counts Reported in the Literature of various rankings, the nomenclature follows Chromosome counts for 6 of the taxa sur- several sources. These include Rollins (1993), veyed here have been previously reported in Hitchcock (1950), Holmgren (2005), and Al- the literature. These are L. dictyotum A. Gray Shehbaz and Gaskin (2010). (2n = 32; Mummenhoff et al. 2004), L. latifolium L. (2n = 24), L. lasiocarpum Nutt. ex Flow Cytometry Torrey & Gray (2n = 32), L. integrifolium Nutt. Live leaf materials were collected from ex Torrey & Gray var. heterophyllum S. Wats greenhouse-grown Lepidium and kept on ice (2n = 16), L. montanum Nutt. ex Torrey & Gray until processing occurred, generally within var. canescens (Thell.) C.L. Hitchc. (2n = 32), 1–3 h. Leaves were placed in a petri dish with L. montanum var. jonesii (Rydb.) C.L. Hitchc. equal amounts of leaves from the size standard (2n = 32), and L. montanum var. montanum (Glycine max (L.) Merr. ‘Polanka’) maintained (2n = 16; Warwick and Al-Shehbaz 2006). in a growth chamber at UAF. Leaf material was chopped in 0.5 mL of cold chopping buffer RESULTS using a stainless-steel razor blade. The chopping buffer was modified from Otto (1990) Fifty-eight samples of Lepidium individuals Buffer I by adding 0.5% v/v of Tritonx100 representing 14 species and 11 varieties were rather than Tween 20. As the leaves were surveyed (Table 1). Of these 58 samples, 52 chopped, an additional 0.5 mL of cold chop- (90%) were tetraploids. Ploidy levels for the ping buffer was added. The samples were remaining taxa surveyed here are reported for filtered through a 30-mm Partec CellTrics© the first time. For the other 3 taxa in this sur- filter and centrifuged for 20s at 3500 rpm. The vey that were not tetraploids, the range of supernatant was drawn off, and 2 mL of ploidy levels included diploid and hexaploid. RNase was added to the pellet. The pellet The taxa having other than a tetraploid count was resuspended in 0.2 mL of propidium were L. integrifolium (hexaploid), L. montanum iodide staining buffer (28.65 g dibasic sodium var. canescens (diploid), and L. montanum var. phosphate, 50 mg propidium iodide, 200 mL cinereum (C.L. Hitchc.) Rollins (syn. var. stellae deionized water). Samples were stained in Welsh & Reveal) (hexaploid). the dark for 40 min prior to flow cytometry The distributions of ploidy levels across application. species surveyed are shown in Fig. 1. The 372 WESTERN NORTH AMERICAN NATURALIST [Volume 74 (1971), 2n = 32 (2004), 2n = 32 Queirós (1973), 2n = 24; and others, see Warwick For Al-Shehbaz (2006) Queirós (1979), 2n = 48 Monument, NM Monument, NM Monument, NM 8528b8528 NV Buffalo Well, NV Buffalo Well, 1.229 1.458 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8529 UT Valley, Paradise 1.613 2n = 32 Tetraploid, 8530 Battle Mountain, UT 1.587 2n = 32 Tetraploid, Rollins and Rüdenberg 844385198519c Sweetwater Canyon, NM Dinosaur National Monument, CO Dinosaur National Monument, CO 1.738 1.451 2n = 32 Tetraploid, 1.526 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8509b8909c2 White Sands National Sands National White 8518a28518b38525 Hamilton, CO 1.346 Hamilton, CO 1.327 2n = 32 Tetraploid, ID North rim of Snake River, 2n = 32 Tetraploid, 1.38 1.384 1.402 2n = 32 Tetraploid, 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8534 NV Ely, 0.768 Diploid, 2n = 16 10502 WY Big Piney, 1.619 2n = 32 Tetraploid, Rollins (1993), n = 16 10624 Hay Gulch, CO 1.444 2n = 32 Tetraploid, 1045610452 UT24083 Vernal, Cokeville, WY UT Cedar City, 1.555 1.307 2n = 32 1.239 Tetraploid, 2n = 32 Tetraploid, 2n = 32 Tetraploid, Voucher Voucher 10624 (f/d) Hay Gulch, CO 1.699 2n = 32 Tetraploid, alyssoides stipulata species, voucher numbers, collection locations, 2C values, ploidy levels, and previous literature reports. heterophyllum canescens eastwoodiae Reveal 8520 Duchesne, UT 1.551 2n = 32 Tetraploid, Nutt. ex Nutt. ex var. 8522 Area, WY Bear River Wildlife 2.001 2n = 32 Tetraploid, var. var. A. Gray var. A. Gray var. var. A. Gray 8527 North of Sparks, NV 1.228 2n = 32 Tetraploid, Mummenhoff et al. L. 8534 NV Ely, 0.892 Diploid, 2n = 16 Mulligan (1957), 2n = 24; (E.L. Greene) 8518 Hamilton, CO 1.603 2n = 32 Tetraploid, S. Wats. var. var. Wats. S. Lepidium Rollins 8525 ID North rim of Snake River, 1.506 2n = 32 Tetraploid, S.L. Welsh & Goodrich Welsh S.L. 10465 WY Wamsutter, 1.75 2n = 32 Tetraploid, 1. ABLE T (Wooton) Rollins(Wooton) 8909a White Sands National 1.357 2n = 32 Tetraploid, Torrey & GrayTorrey S. Wats. 8522 Area, WY Bear River Wildlife 3.117 2n = 64 Hexaploid, Species number Location 2C Inferred ploidy level literature reports Previous L. alyssoides L. huberi L. alyssoides L. barnebyanum L. davisii L. dictyotum L. crenatum L. fremontii L. integrifolium L. integrifolium L. latifolium L. montanum 2014] GENOMIC SIZE, PLOIDY LEVELS OF LEPIDIUM 373 Rollins and Rüdenberg (1971), n = 16; Rollins and Rüdenberg (1977), n = 16; Rollins (1993), 2n 32 Huntington Creek, NV 8510a8511a8511b18511c Columbia, NM NM Lordsburg, NM Lordsburg, NM Lordsburg, 0.699 1.319 1.316 Diploid, 2n = 16 1.354 2n = 32 Tetraploid, 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8521c8521c8532 UT Vernal, 8531 UT Vernal, 8516c3 Bridges along 8516c3 Twin NV Whirlwind Valley, CO Powderhorn, CO Powderhorn, 1.565 1.219 1.516 1.479 2n = 32 Tetraploid, 1.419 2n = 32 Tetraploid, 2n = 32 Tetraploid, 1.347 2n = 32 Tetraploid, Rollins (1993), n = 16 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8524a38524b8524c1 Hollbrook Ranch, NV Hollbrook Ranch, NV Hollbrook Ranch, NV 1.533 1.516 1.537 2n = 32 Tetraploid, 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8517a8517b8517c Gypsum, CO Gypsum, CO Gypsum, CO 1.555 1.439 2n = 32 Tetraploid, 1.444 2n = 32 Tetraploid, 2n = 32 Tetraploid, 8523a8523c2 NV Hollbrook Spring, NV Hollbrook Spring, 0.869 0.929 Diploid, 2n = 16 Diploid, 2n = 16 716087160871608 CO Mesa City, CO Mesa City, CO Mesa City, 1.271 1.895 2n = 32 Tetraploid, 2.123 2n = 32 Tetraploid, 2n = 32 Tetraploid, 24136 AZ Fredonia, 3.165 2n = 64 Hexaploid, Voucher Voucher Rollins) (Rydb.) (Rydb.) 8537 UT Vernal, 1.486 2n = 32 Tetraploid, Schaack et al. (1984), n = 16; wyomingense montanum tenellum coloradense jonesii cinereum (C.L. Hitchc.) 10500 WY Lone Tree, 1.606 2n = 32 Tetraploid, var. var. var. var. var. var. var. var. var. Wooten 8511 dry NM Lordsburg, 0.631 Diploid, 2n = 16 (Rollins) Al-Shehbaz 10524 Mountain, NV Table 1.658 2n = 32 Tetraploid, S. Wats.S. 8533 NV Jake’s Valley, 1.4 2n = 32 Tetraploid, Welsh & GoodrichWelsh 24080 Mountains, UT San Francisco 0.908 Diploid, 2n = 16 1. Continued. Stroganowia tiehmii ABLE (L.O. Williams) C.L. Hitchc. Williams) (L.O. 71608C.L. Hitchc. var. CO Mesa City, 2.044 2n = 32 Tetraploid, (syn. C.L. Hitchc. Rollins 8517b Gypsum, CO 1.439 2n = 32 Tetraploid, T L. ostleri L. montanum L. nanum L. thurberii L. tiehmii L. montanum L. montanum L. montanum L. montanum Species number Location 2C Inferred ploidy level literature reports Previous L. montanum 374 WESTERN NORTH AMERICAN NATURALIST [Volume 74 2C jonesii stipulata L. ostleri tenellum L. davisii L. huberi L. tiehmii cinereum L. nanum alyssoides montanum L. thurberii var. canescens L. latifolium L. crenatum L. dictyotum coloradense var. eastwoodiae var. var. wyomingense heterophyllum L. integrifolium var. var. var. var. L. barnebyanum var. var. var. var. L. fremontii L. montanum L. montanum L. montanum L. alyssoides L. montanum L. montanum L. montanum L. alyssoides L. montanum L. integrifolium

Fig. 1. Distribution of DNA content (2C) ranges across all Lepidium species surveyed. variation of DNA content (2C value) of the Though the amount of DNA may vary be- species surveyed shows the overwhelming tween species and within infraspecific taxa, occurrence of tetraploids throughout the group there are typically no differences in ploidy of 14 species and 11 varieties sampled. level between a species and its varieties, ex- Occurrences of various ploidy levels were cept for L. montanum var. cinereum, which scattered across the Intermountain West. Based was found to have both tetraploid and hexa- on the 58 samples surveyed, there are no obvi- ploid counts. ous patterns of ploidy levels associated with landscape type, geographic range, or species DISCUSSION complex (Fig. 2). Though there are differences in microhabitat preferences among most of the With the high abundance and widespread taxa, ploidy levels were not associated with occurrence of polyploids, especially tetraploids, any particular landscape or habitat feature at in the Lepidium surveyed from the Inter- the collection sites of the plant material. It mountain West, ploidy level does not provide appears that ploidy levels, excepting tetra- much insight for explaining morphological ploids, vary randomly and are not influenced differences or geographic patterns. However, by landscape, habitat, or geographic isolation. there are a few noteworthy observations. 2014] GENOMIC SIZE, PLOIDY LEVELS OF LEPIDIUM 375

Fig. 2. Distribution of Lepidium with various ploidy levels in the Intermountain West.

Ploidy levels in Lepidium as a whole show that is from a collection of var. stellae, which has it is not unusual for a single taxon to have been submerged into the concept of var. more than one ploidy level. Examples of species cinereum (Al-Shehbaz and Gaskin 2010). How- with more than one ploidy level are L. lati- ever, it is important to note that the results folium (diploid and hexaploid), L. integrifolium of this survey may not support a significant (tetraploid, hexaploid, and octoploid), L. mon- inference about the lack of correlation between tanum var. canescens (diploid and tetraploid), ploidy level and taxonomic, geographic, or L. montanum var. jonesii (diploid [Warwick habitat group because the number of non- and Al-Shehbaz 2006] and tetraploid), and L. tetraploid species was so small. thurberi (diploid and tetraploid). Of the 7 Historically, the use of chromosome num- varieties surveyed in the L. montanum com- bers for classification purposes in vascular plex, only var. cinereum and var. canescens had plant taxonomy has long been limited to sup- more than one ploidy level. Variety cinereum porting or defining the concept of a species. is reported as both tetraploid and hexaploid, The shape and number of chromosomes are and var. canescens as both diploid and tetra- not weighed differently than any other mor- ploid. The hexaploid reported for var. cinereum phological feature for taxonomic purposes 376 WESTERN NORTH AMERICAN NATURALIST [Volume 74

(Stacy 1980). This is probably a result of the these FC observations and indications of input frequent variation in chromosome or ploidy of different parental DNA stock based on vari- levels. The lack of use of ploidy level to sup- able sizes of DNA content cannot be conclu- port species concepts is no doubt linked to the sively resolved. Likewise, with no association fact that over 70% of angiosperm plants have of geographic ploidy levels with geographic ploidy level increases in their evolutionary ranges or habitats and with variability of DNA histories (Meyers and Levin 2006). Because content between Lepidium taxa, mere ploidy multiple ploidy levels are common in most levels may not be useful for taxonomic pur- angiosperm groups, it would appear that little poses. However, ploidy levels do indicate the distinction among taxa could be obtained from need for the construction of gene trees to ade- the variability. quately treat these diverse native species of Stebbins (1971) proposed that a young poly- Lepidium in the Intermountain West. ploid complex would contain many diploids and a few tetraploids. As the complex ages, ACKNOWLEDGMENTS more species would become polyploids and higher ploidy levels would develop. As time The quality and content of information progresses, the ancestor diploids would ulti- reported here would not have been possible mately die out, resulting in greater difficulty without the guidance, comments, and reviews in describing the evolutionary ancestry. Almost provided by Diana Wolf and Gary Laursen of all species in this survey were of higher ploidy the University of Alaska and Ihsan Al-Shehbaz levels, with 90% being tetraploids. In addi- of the Missouri Botanical Garden. Funding tion, the 11 native North American species of for this effort was made possible by the U.S. Lepidium with reported chromosome counts Army Corps of Engineers Engineering and were 90% dominated by tetraploids (Warwick Research Development Center/Cold Regions and Al-Shehbaz 2006). Using Stebbins’s widely Research and Engineering Laboratory (ERDC/ accepted concept (Meyers and Levin 2006), CRREL), Hanover, New Hampshire. the Intermountain West Lepidium complex can be described as an evolutionarily young to moderate-aged species group with a reticulate LITERATURE CITED evolutionary past. The indication of a reticu- AL-SHEHBAZ, I.A. 1986. New wool-alien Cruciferae (Bras- late evolutionary past has been demonstrated sicaceae) in eastern North America: Lepidium and in Lepidium by incongruences in gene trees Sisymbrium. Rhodora 88:347–356. (Bowman et al. 1999, Mummenhoff et al. 2001, ______. 1988. The genera of Arabideae (Cruciferae; Bras- 2004). Bowman et al. (1999) and Mummenhoff sicaceae) in the southeastern United States. Journal of the Arnold Arboretum 69:85–166. et al. (2001, 2004) suggest that most polyploids ______. 2012. A generic and tribal synopsis of the Brassi- in Lepidium are allopolyploid. On the basis caceae (Cruciferae). Taxon 61:931–954. of previous cpDNA and ITS sequence data, AL-SHEHBAZ, I.A., AND J. GASKIN. 2010. Lepidium L. in allopolyploidization has been strongly favored Brassicaceae. Pages 226–594 in Flora of North America Editorial Committee, editors, Flora of North to explain gene tree patterns (Mummenhoff et America. Volume 7, Magnoliophyta: Salicaceae to al. 2001, 2004). The influence of a reticulate Brassicaceae: north of Mexico. Oxford University evolutionary past in the Intermountain West Press, New York, NY. region in this genus, coupled with both high BENNETT, M.D., P. BHANDOL, AND I.J. LEITCH. 2000. occurrence of polyploidy across all species and Nuclear DNA amounts in angiosperms and their modern uses—807 new estimates. Annals of Botany highly mobile seeds that are easily transported (Oxford) 86:859–909. by avian species to allow for mixing of popu - BENNETT, M.D., AND I.J. LEITCH. 2005. Nuclear DNA lations and species (Al-Shehbaz 1986), pro- amounts in angiosperms—progress, problems and vides for a diverse array of polyploid geno- prospects. Annals of Botany 95:45–90. ______. 2012. Plant DNA C-values Database. Release 6.0, types (Soltis and Soltis 1999). This evolutionary December 2012. Available from: http://www.kew background may be setting the challenging .org/cvalues/. stage for adequately classifying these native BOWMAN, J.L., H. BRÜGGEMANN, J.-Y. LEE, AND K. MUM- intermountain species. MENHOFF. 1999. Evolutionary changes in floral In future research on Intermountain West structure within Lepidium L. (Brassicaceae). Inter- national Journal of Plant Sciences 160:917–929. Lepidium, DNA sequences will be analyzed CALFLORA. 2008. Information on California plants for and gene trees developed. Without gene trees, education, research and conservation. The Calflora 2014] GENOMIC SIZE, PLOIDY LEVELS OF LEPIDIUM 377

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