Cornus × elwinortonii and Cornus × rutgersensis (Cornaceae), new names for two artificially produced hybrids of big-bracted dogwoods

Abstract Big-bracted dogwoods (Cornus sp.) are well-known plants in North America and eastern Asia where they occur as wild, generally spring-flowering understory trees. They are also popular ornamental landscape plants, and many economically important cultivars are propagated and sold across North America, Europe, and Asia. Starting in the late 1960s, Elwin Orton of Rutgers University in New Jersey (USA) utilized three geographically disjunct species of dogwoods, Cornus florida (eastern North America), Cornus nuttallii (western North America), and Cornus kousa (East Asia), in an extensive interspecific hybridization program. He was successful in developing the first-ever interspecific F1 hybrids of these species, several of which have become staple items in the ornamental nursery trade due to their enhanced ornamental qualities and resistance to diseases. The original F1 plants are still alive at Rutgers University. While they have been available for decades in horticultural commerce, the interspecific hybrid crosses were never formally described and their scientific hybrid names were never published. For the Cornus kousa × Cornus florida hybrids, the name Cornus ‘rutgersensis’ has been used on occasion in the horticultural trade, but without proper citation and description. Here, it is formally named Cornus × rutgersensis Mattera, T. Molnar, & Struwe, hybr. nov. For the Cornus kousa × Cornus nuttallii hybrids, no previous name has been used, and it is hereby named Cornus × elwinortonii Mattera, T. Molnar, & Struwe, hybr. nov. The need for providing scientific names for commonly used horticultural hybrids is discussed. Holotype material for both hybrid names was collected from the original F1 hybrids for full documentation, typification, and description. The comparative intermediate development of leaves, inflorescence structures, and fruit types of the hybrids and their parents is discussed and illustrated. Etymology, phenology, and cultivation aspects of these hybrids and their cultivars including backcrosses to Cornus kousa are also presented.


Introduction
Th e circumboreal genus Cornus L. (Cornaceae, Cornales; APG III 2009) contains about 60 species divided into ten subgenera (Fan and Xiang 2001). Species in this genus express a wide variety of morphologies, from low herbaceous ground covers, such as the boreal-temperate species C. suecica L., to multi-stemmed shrubs, such as C. sericea L. It also includes small to large trees, such as C. kousa Buerger ex Miq. and C. nuttallii Audubon ex Torr. & A.Gray, the latter of which can grow up to 24 m tall. Some taxonomists have divided the genus up into six genera, but molecular studies have shown that Cornus in the current circumscription is monophyletic (Xiang et al. 2006).
Several species of Cornus have large, showy petaloid bracts located under tight head-like, multi-fl owered infl orescences. Th ese species form the monophyletic bigbracted (BB) clade sensu Xiang et al. 2006, and are mostly spring-fl owering trees of North American and East Asian forests. Th e members of this clade are classifi ed into three diff erent subgenera: Cynoxylon, Discocrania, and Syncarpea (Xiang et al. 2006). Th e most commonly known big-bracted species in North America are C. fl orida L. and C. nuttallii of subgenus Cynoxylon and C. kousa of subgenus Syncarpea. Seed and clonally propagated big-bracted dogwoods are popular ornamental landscape trees in subtropical to temperate regions around the world. Th eir most conspicuous characteristics are their large, white or red petaloid fl oral bracts, showy red fruits, and brightly colored fall foliage (Li et al. 2009). Cornus kousa can be easily distinguished from the other two species by its round, fl eshy multiple fused fruits formed from a whole fl ower head (as opposed to single, separate drupes from each fl ower arranged in clusters). It can also be identifi ed by its acute or acuminate fl oral bracts, whereas the others have bracts that are rounded or retuse (Harrison 2009).
Typical horticultural uses of the big-bracted dogwoods include container, specimen, or shade plantings in suburban landscapes, display gardens, and parks Watson 1993a, b, Mohlenrock 2006). In the eastern and southeastern USA, Cornus fl orida is a common component of native deciduous forests, gardens, and home landscapes. It is among the fi rst trees to bloom with conspicuous fl owers in the spring in North America, with a range of cultivars available that express dwarf to vigorous growth habits and white, pink or red fl oral bracts. Cornus kousa is also a common component of ornamental landscapes in the eastern USA. It blooms about a month later than C. fl orida (after the leaves have developed), has a more vase-shaped growth habit, and most have white fl oral bracts, although a few forms with light pink bracts exist (Cappiello andShadow 2005, Dirr 2009, Rhoades et al. 2011). Th e use of C. nuttallii in landscaping is much more limited than the former two species, due to limited winter hardiness in the eastern USA and it is cultivated mostly in the Pacifi c Northwest (USA), where it is native. Dogwood sales in the USA account for over 11% of the total deciduous fl owering tree market, amounting to nearly 31 million USD in 2009 (Fulcher et al. 2012, NASS 2007. Th e Rutgers University dogwood breeding program began in 1965 under the direction of horticultural plant breeder Dr. Elwin Orton. Th e early goals of the program were to develop novel cultivars of Cornus fl orida and C. kousa with improved aesthetic qualities, including pink and red fl oral bracts, unique growth habits, and superior disease resistance. Several years after the program started, attention was turned toward developing interspecifi c hybrids between these two species as well as between C. kousa and C. nuttallii, to help reach these goals (Elwin Orton personal communication). Because of diff erences in fl owering times between the species, which can span more than a month, Orton used two approaches to make the hybrid crosses. First, he collected, dried, and stored pollen from earlier fl owering plants to apply to the stigmas of those that bloomed later in the fi eld and greenhouse. Second, he manipulated bloom times through the careful use of cold chambers and warm greenhouses to artifi cially break dormancy and match fl owering times of container-grown plants to those in the fi eld (E. Orton personal communication). Orton was ultimately successful in his interspecifi c hybridization attempts and is credited as being one of the fi rst to create C. fl orida × C. kousa and C. kousa × C. nuttallii F 1 hybrids (Dirr 2009). To date, eleven interspecifi c cultivars, comprising eight from C. fl orida × C. kousa crosses and three from C. kousa × C. nuttallii hybrids, have been named, released, and patented through the Rutgers University dogwood breeding program (Table 1). Th e two classes of interspecifi c hybrids display intermediate morphological and phenological characteristics between the parental species (Cappiello and Shadow 2005, Dirr 2009, E. Orton personal communication, Orton 1990a, 1990b, 1990c, 1990d, 1990e, 1991, Orton and Gant 1993a, 2006a, 2006b, 2011. Many also show increased vigor (rates of growth) compared to their parent species, as well as improved stress tolerance.
According to the International Code of Nomenclature for algae, fungi, and plants (abbreviated hereafter as ICN), a hybrid between two plant species can be given two types of scientifi c names to classify them within the taxonomic system of plant biodiversity (McNeill et al. 2012: Art. H1). Either the hybrid is listed with the name of the two parents separated by a multiplication (×) sign, such as in the oak hybrid Quercus alba × Quercus bicolor, or they may be given a unique name with the species epithet preceded by a multiplication (×) sign, such as Quercus × jackiana for the same hybrid (Haines 2011). For hybrids in horticulture and commerce, the second option is preferred since it provides a simpler name that is easier for horticulturalists and the public to learn, catalogue, use on labels, and remember. It also provides a scientifi c name that fi ts into existing databases already in use for commercial plants. For the two fl owering dogwood hybrids discussed here, no formal scientifi c names have been proposed, although 'Cornus × rutgersiensis' and 'Cornus × rutgersensis' (sometimes without the multiplication sign, ×) have been used in popular and horticultural literature for many years to indicate Cornus fl orida × Cornus kousa hybrids (e.g., Gayraud 2013, Cubey et al. 2014Shearer andRanney 2013, Wikipedia 2014). Th ose names are currently invalid since, according to the ICN, all proposed scientifi c names, including hybrid names, require that they be formally published and described and be represented by a type specimen. A type specimen is the specimen to which the name is permanently attached and which is publicly available for consultation (McNeill et al. 2012).
Th e name Cornus × rutgersensis is proposed for the hybrid C. kousa × C. fl orida. A new name is also proposed, Cornus × elwinortonii, honoring our colleague Dr. Elwin Orton, for the hybrid he created between C. kousa and C. nuttallii. Full morphological descriptions, typifi cation, illustrations, horticultural information with cultivar names, disease response, and a discussion on the formation of intermediate morphological traits with regard to leaf size, infl orescence structure, and fruits are provided for each of these new names. In doing this, we provide both formal names and summarize information of general botanical interest of these popular garden plants for botanists and horticulturalists. Description. Tree with upright or rounded habit,10 m in height at maturity. Bark rough, as sandpaper, with exfoliation at the base of the trunk; lenticels abundant, 1.25-1.75 × 0.40-0.65 mm. Leaves opposite, simple, elliptic, ovate to obovate, 10.3-15.3 × 5.9-9.1 cm; base attenuate to oblique; margin entire to slightly wavy, cuneate/crenate; apex apiculate; venation with 5 (or 6) pairs of secondary veins; midrib and abaxial surfaces with conspicuous indumentum of short, fi ne, downy, whitish beige trichomes with occasional dark tufts of longer brown trichomes in the axils of midvein and secondary veins, indumentum less dense on adaxial surfaces. Overwintering infl orescence buds not covered by the two outer opposing pairs of vegetative bracts, minimally covered by two inner opposing pairs of fl oral bracts (0-40% coverage; fl oral bracts more developed than in C. kousa during overwintering). Infl orescence capitate, globose, with 55-80 sessile fl owers per head, subtended by 4 (rarely 5 or 6) simple entire, decussate pairs of bracts. Bracts petaloid at anthesis, ovate to lanceolate, sometimes wider than long, overlapping or not when fully developed, 5-8 cm long, 3.5-7.0 cm wide, usually white, or occasionally pink; base tapering to point of attachment; apex acuminate to cuspidate. Peduncle 1.5-8.0 cm long at time of fl owering. Flowers actinomorphic, bisexual, 4-merous. Calyx lobes ovate; apex obtuse. Corolla lobes obovate, apex slightly acute. Stamens 4, exserted from corolla mouth, inserted in corolla lobe sinuses; fi laments 1.5-2.5 mm long, 0.2-0.5 mm wide; anthers ovoid, bae sagittate, longitudinally dehiscent, 1.0-1.1 × ca. 0.25 mm; pollen less prevalent on hybrids compared to parent species, white or yellow-brown. Gynoecium epigynous, with nectar disc; ovary syncarpous; style 1, 1.5-2.5 mm long, exserted from corolla; stigma indistinct, ca. 0.4 mm long. Fruit either many drupes tightly compressed together, or a multiple fruit formed from 1-seeded drupelets forming a mounded raspberry-like fruit, often parthenocarpic. Ecology and phenology. In New Jersey, Cornus × elwinortonii fl owers during May and June, and the fruit matures from September to October. Various beetles and bees visit the fl owers at anthesis, with an abundance of goldenrod soldier beetles (Chauliognathus pensylvanicus) frequently observed by the authors. Th e mostly sterile fruit with little pulp generally senesces and falls from the trees by October. Th e few fruits with a developing seed are swollen and have more pulp. We suspect they are eaten by insects and birds. Etymology. Th e epithet, elwinortonii, honors the prominent dogwood breeder Dr. Elwin Orton (b. 1930), Professor Emeritus in the Department of Plant Biology and Pathology at Rutgers University. He was the fi rst to successfully develop and release a hybrid between Cornus kousa and C. nuttallii. Th e common name, Orton's dogwood, is proposed for this hybrid.
Distribution. Cornus × elwinortonii is known only from cultivation, although at times it produces viable seeds. Th e natural range of the staminate parent, C. nuttallii, is in western North America from the lowlands of British Columbia (Canada) to southern California (USA), with a small isolated population in northern Idaho (USA, Keir et al. 2011, Klinka et al. 2000. Th e other parent, C. kousa, is native to mesic forests of Japan, Korea andChina (Flint 1997, Xiang andBouff ord 2005). Cornus nuttallii cannot withstand sustained periods of frost, thus limiting its natural and cultivated range. In contrast, C. kousa can be cultivated throughout much of the USA; Europe, and Asia in U.S. Department of Agriculture cold hardiness zones 6a-9a (Daly et al. 2012, Flint 1997. Th e hybrid C.× elwinortonii can survive sustained frosts and has a similar climate range as C. kousa. However, for some cultivars of C. × elwinortonii the fl oral buds are less cold hardy than in the parent C. kousa. In colder climates, includ-ing in New Brunswick, NJ, where the hybrid originated, fl ower buds can be damaged by cold winter temperatures, leading to a reduced fl oral bract display in the spring (E. Orton personal communication).
Horticulture. Plants of Cornus × elwinortonii are grown as landscape ornamentals and can be cultivated wherever C. kousa, C. nuttallii, and C. fl orida may be grown. Th is hybrid is cultivated for its all-year round appeal: fl oral bracts, attractive foliage, autumn color and appealing bark (Eberts 2007) Cornus × elwinortonii is typically propagated asexually through budding and grafting on seedling rootstocks of C. kousa or C. fl orida. Patented and trademarked cultivars that belong to this hybrid include 'KN4-43' Starlight® (F 1 ), 'KN 30-8' Venus® (fi rst backcross to C. kousa), and 'KN144-2' Rosy Teacups® (third serial backcross to C. kousa; Table 1). We know of no other commercially available cultivars of Cornus × elwinortonii.
Disease response. While dogwood anthracnose caused by the fungus Discula destructiva Redlin is known to infect and kill C. nuttallii, it has not been reported to be a signifi cant problem on either C. kousa or C. × elwinortonii (Daughtrey and Hibben 1994;Fulcher et al. 2012;Hagan et al. 1998).
Parent source materials. Th e parents of the described type F 1 hybrid ('Rutgan' Stellar Pink®) are Cornus kousa K2 (female) grown at Rutgers Gardens from a seedling received from Ben C. Blackburn, Willowwood Arboretum (Gladstone, NJ) in May of 1949, and C. fl orida 'Sweetwater Red' (male), received from Boyd Nursery (McMinnville, TN) and planted at Rutgers Gardens.
Ecology and phenology. Cornus × rutgersensis fl owers in New Jersey (USA) in May; the fruits mature from September to October. Adrenid and halictid bees and cerambycid beetles pollinate the fl owers of C. kousa while only adrenid and halictid bees pollinate C. fl orida (Rhoades et al. 2011). It is believed that the same insects visit the fl owers of the hybrid. All cultivars released to the public, except 'KF111-1' Hype-rion® (fi rst backcross to C. kousa), are sterile. Sterile specimens produce very little pulp in the fruit and no fully formed seeds. It is unlikely that these aborted fruits serve as a signifi cant food source for insects or birds. Hyperion® produces fruits that are more similar to C. kousa and likely serve as a food source for wild animals, although there are no studies to substantiate this assumption.
Etymology. Th e epithet rutgersensis is based on Rutgers University, Th e State University of New Jersey, the academic home of Dr. Elwin Orton's dogwood breeding program, which is now continued by co-author Th omas Molnar. Rutgers University was founded in 1766 in New Brunswick, NJ, and was named in 1825 after Colonel Henry Rutgers, a US Revolutionary War veteran (Rutgers University 2014). We suggest the common name Rutgers' dogwood for this hybrid.
Distribution. Cornus × rutgersensis is known only from cultivation. One of the parent species, C. fl orida, an understory tree in mesic forests (Fulcher et al. 2012, Hillier Nurseries 2002, Porter 1903, Schwartz 1994, Wennerberg 2006, ranges from southern Maine to Florida, and as far west as Texas in the USA (Mohlenrock 2006, Schwartz 1994, Wennerberg 2006. Cornus kousa occurs in mesic forests in Japan, Korea, andChina (Flint 1997, Xiang andBouff ord 2005). No formal studies have been done to determine climate range for C. × rutgersensis; however, it is generally believed that its range is similar and intermediate between the two parent species C. fl orida and C. kousa.
Disease response. Cornus × rutgersensis shows resistance to dogwood anthracnose and resistance or high levels of tolerance to powdery mildew (Erysiphe pulchra and Phyllactinia guttata; Li et al. 2009, Ranney et al. 1995, Trigiano et al. 2005. Additional material examined. Additional collections from the same individual from which the holotype was collected, but at other dates: R. Mattera 26, R. Mattera 28, R. Mattera 30, R. Mattera 32, will all be deposited at CHR, NY, and MO).

Morphological intermediacy in hybrids.
Interspecifi c hybrids are commonly intermediate in their morphology between their parents (e.g., Tovar-Sanchez and Oyama 2004). However, in hybrids between the big-bracted dogwoods, there is the added complication of the parental species having either a multiple, berry-like fruit or singleseeded drupes, and remarkably diff erent infl orescence buds, bract morphology and phenological development. Despite such large diff erences, the hybrids clearly express intermediate phenotypes and provide good examples of 'halfway' morphologies created through hybridization. Intermediate traits include leaf size, infl orescence structure, and fruit type, which are three important ornamental characteristics of big-bracted dogwoods. Th e shape of the bract shape is also intermediate in these hybrids, leading to increased variation in bract shape. Also, the intermediate fl owering times allow for a lengthening of the display of the ornamental bracts across the big-bracted clade. Both hybrids discussed in this paper also display novel characteristics not seen in previous dogwood cultivars. For example, 'KN30-4' Venus® displays larger fl oral bracts than in other hybrid cultivars or in the species of Cornus known to us.
Generally, C. × rutgersensis and its parents display similar tree shape and form, but the hybrid displays increased vigor and growth (Fig. 4). In C. × elwinortonii, tree shape and growth habit appear similar to the parents, C. kousa and C. nuttallii, but the hybrid is signifi cantly more vigorous than C. kousa and shows increased growth in younger trees. Cornus × elwinortonii can be signifi cantly larger in stature (to 8 m; Fig. 2) than most trees of C. kousa (to 6 m; Gilman and Watson 1993b), but hybrid tends to be signifi cantly shorter than C. nuttallii (to 12 m, occasionally to 22.9 m; Gucker 2005).
Th e leaves of C. × rutgersensis are intermediate between the two parents, being longer and wider than C. kousa and shorter and narrower than C. fl orida. A similar phenomenon was recorded in the Quercus crassifolia Bonpl. × Q. crassipes Bonpl. hybrid complex (Fagaceae; Tovar-Sanchez and Oyama 2004) and in crosses between the herbs Brassica oleracea L. and Sinapis alba L. (Brassicaceae;Hansen and Earle 1996). Th e leaves of C. nuttallii and C. kousa are narrower (5-7 cm) than their off spring, C. × elwinortonii (5-8 cm), and the leaves of the hybrid can also have a crinkled appearance, which is not characteristic of either parent. Such novel hybrid characteristics are not unusual and have also been reported in the Quercus crassifolia × Q. crassipes complex (Tovar-Sanchez and Oyama 2004) and in Carica papaya L. × Vasconcellea caulifl ora (Jacq.) A.DC. (reported as C. caulifl ora Jacq.; Caricaceae; Magdalita et al. 1996).
Infl orescence bud morphology and development shows dramatic diff erences between the parents of C. × rutgersensis and is also correlated with large diff erences in fl oral bract display (and anthesis). Th e fl oral bracts of Cornus fl orida are displayed before vegetative bud-break in early spring, whereas in C. kousa the fl oral bracts are displayed after the foliage is fully developed. In C. fl orida, the infl orescence bud consists of two pairs of fl oral bracts (inner and outer) tightly clinging to a well-developed infl orescence head. Underdeveloped vegetative bracts are present but do not cover the infl orescence. Cornus kousa has two pairs of fl oral bracts that tightly cling to the underdeveloped infl orescence. In addition, they are tightly covered by two pairs of vegetative bracts. Th e hybrid displays an intermediate fl ower bud in which fl oral bracts cling to the infl orescence and vegetative bracts cling loosely to the fl ower head ( Fig. 3c and 5 (Oleaceae;Gerard et al. 2006). Notably, in C. × rutgersensis, the fl oral bracts tend to only weakly cover the infl orescence during overwintering, resulting in 10-45% of the fl owers being naked (exposed).
Diff erences in the infl orescence buds also exist for C. × elwinortonii and its parents, C. nuttallii and C. kousa. Th e underdeveloped infl orescence head in C. kousa is tightly covered by two pairs of fl oral and vegetative bracts. Cornus nuttallii has a completely exposed infl orescence head, where the small fl oral and vegetative bracts do not cover the developing fl ower buds. Cornus nuttallii, native to the Pacifi c Northwest (USA), is exposed to milder winter temperatures than C. kousa from eastern Asia. Cornus × elwinortonii displays an intermediate bud ranging from completely exposed to completely covered. In Cornus × rutgersensis, there is strong variation in the degree of coverage by the bracts, with 10-45% naked to nearly completely covered fl oral buds.
Distinct diff erences between infl orescence architectures can also be observed between parents and their hybrids. In Cornus kousa, all fl owers in the infl orescence are fused, creating a densely merged ball of fl owers, while in C. fl orida the fl owers are not fused, creating a more open structure. Th e fl owers in their hybrid, C. × rutgersensis, are densely packed and at fi rst appear to be fused together; however, they are separate even if closely positioned ( Fig. 3 and Fig. 4A). Th e number of fl owers in each infl orescence varies greatly within big-bracted dogwoods, from a few dozen to over one hundred. Th e hybrids also show intermediacy in the number of fl owers: C. × rutgersensis (30-50 fl owers/head) from parents C. fl orida (20-30) and C. kousa (20-50), and C. × elwinortonii (55-80) from parents C. kousa (20-60) and C. nuttallii (70-100).
In C. fl orida, the individual fl owers develop into single-seeded drupes, while in C. kousa the fused fl owers develop into single-seeded druplets that are fused into a multiple, berry-like fruit (Fig. 5). Th e nearly always sterile hybrid C. × rutgersensis may produce parthenocarpic fruit displaying intermediate characteristics (Fig. 5). Fruits containing seeds swell and develop into individual drupes or drupelets. Th is is the only example we know of where a hybrid has been created between parents with single and multiple fruit types. Th e hybrid between Jatropha curcas L. and J. integerrima Jacq., formed from the crossing of plants with large drupaceous fruits (J. curcas) and small deeply lobed capsules, displayed an intermediate fruit shape between two diff erent fruit types as well (Rupert et al. 1970;Sujatha and Prabakaran 2002).
Success of hybrids. Ornamental plants play an important role in society, providing aesthetic value, shade, wildlife habitat and food, and soil stabilization. As popular ornamental trees in temperate and sub-tropical regions worldwide, improved cultivars of big-bracted dogwoods are desired. Demand for novel, vigorous, and disease-resistant plant material is high; however, limited genetic variability can exist for some traits. For example, there are only a few cultivars of C. fl orida that express resistance to powdery mildew (Windham et al. 2003, Windham andWitte 1998) and the fl oral bracts of C. kousa and C. nuttallii lack the dark red of the most successful C. fl orida cultivars (Cappiello andShadow 2005, Dirr 2009). Orton's use of interspecifi c hybridization to develop the novel plants described here (Cornus × rutgersensis and Cornus × elwinortonii) resulted in the successful development of cultivars with enhanced aesthetic qualities and improved disease resistance.
Upon its introduction to the US from Asia, dogwood anthracnose devastated natural stands of C. fl orida, a plant species highly susceptible to this fungal disease. For example, mortality rates as high as 86% occurred in a ten year period in Connecticut (Holzmueller et al. 2006). Cornus nuttallii is also highly susceptible to dogwood anthracnose. Th e Asian dogwood C. kousa occurs sympatrically with the causal agent of dogwood anthracnose Discula destructiva in Asia, and most cultivars of C. kousa have a high level of tolerance or resistance to this disease (Hibben 1990, Ranney et al. 1995. Because of results from fi eld evaluations and the C. kousa parentage, all of Orton's hybrids were believed to be highly resistant to this disease at the time of their commercial release. Th e Stellar® Series and Jersey Star® releases came at a time when disease incidence was high in the United States. However, Ranney et al. (1995) showed that not all of the Rutgers hybrids maintained resistance over the years, although some still displayed tolerance.
Powdery mildew, believed to be introduced from Asia, is less devastating to natural stands of C. fl orida. Instead, this disease has strongly impacted the nursery industry, raising production costs and reducing aesthetic appeal. Cultivars of C. fl orida display little resistance to this fungal disease. Of more than 100 available cultivars of C. fl orida (Santamour and McArdle 1985), only fi ve ('Jean's Appalachian Snow', 'Karen's Appalachian Blush', 'Kay's Appalachian Mist', 'Appalachian Joy' and 'Cherokee Brave') display high levels of tolerance or resistance to powdery mildew (Li et al. 2009, Ranney et al. 1995. Again, cultivars of C. kousa generally show high levels of tolerance (Li et al. 2009, Ranney et al. 1995. Due to Orton's selection of parents, several cultivars of C. × rutgersensis (e.g., Stellar Pink®, Aurora®, Stardust®, Celestial®, and Constellation®) are resistant to powdery mildew (Li et al. 2009).
Scientifi c naming of horticultural plants. Crucial to communication in all parts of our lives is the naming of objects and phenomena. We need words to tell other people what we are talking about, and the words need to have uniform and clear meanings. For botany, our scientifi c names form such a uniform language that is universal and used in fi elds including biodiversity inventories, phytochemistry, horticulture, crop plants, and other scientifi c and/or economic endeavors. Many scientifi c plant names are listed in the International Plant Names Index (http://www.ipni.org) and in other resources such as fl oras, dictionaries, Th e Plant List (http://www.theplantlist.org/), RHS Plant Finder (http://www.rhs.org.uk/plants/), Encyclopedia for Life (http://eol.org), Wikipedia (http://wikipedia.com). Unfortunately, many misspelled, outdated, unpublished, illegitimate, and invalid names are still in use worldwide in popular literature, websites, and non-taxonomic publications, especially for commonly cultivated and medicinal plants (Bennett and Balick 2014 for examples, see Struwe 2014).
It can be argued that we do not need formal scientifi c names for all artifi cially created hybrid plants, since cultivar and trademark names exist and names of cultivated plants follow Th e International Code of Nomenclature for Cultivated Plants (ICNCP, Brickell et al. 2009). However, names of hybrids following the International Code for algae, fungi, and plants may be useful when cataloging species diversity, natural or human-made, and linking hybrids with their parental species. Cornus × rutgersensis is a name already in use on a global scale, but was never proposed formally according to the rules of the ICN. Validating this name is the simplest way to provide an acceptable and useful name to the horticultural community. Since the second hybrid, C. × elwinortonii, is also a commonly grown and well-known hybrid in gardens, to propose it formally is also useful. Even if self-propagating seedlings from these hybrids are not known, we do know that viable seeds are sometimes produced; making it is possible that spontaneous progeny will arise in the future

Summary
Th e hybrids Cornus × rutgersensis (C. fl orida × C. kousa) and Cornus × elwinortonii (C. kousa × C. nuttallii) were developed at Rutgers University by Dr. Elwin Orton, and are good examples of controlled hybrid crosses showcasing intermediate morphological and phenological characteristics for leaf size, infl orescence bud structure, fl owering time, and fruit structure. Th e horticultural success of big-bracted dogwood hybrids in the nursery and landscape industry can largely be attributed to their inherent disease resistance and enhanced aesthetic qualities that represent novel intermediate phenotypes between their parent species.