Flowering dogwoods (Cornus florida L.) are relatively small deciduous trees that are popular as landscape ornamentals and native to the eastern United States and Canada. Cornus florida is classified in the red-fruited, big-bracted dogwood clade, which also includes C. nuttallii Audubon ex Torr. and A. Gray) (Pacific dogwood) and C. kousa F. Buerger ex Hance (Kousa dogwood; Asian dogwood) (Call et al. 2016; Eyde 1988; Mantooth et al. 2017). Flowering dogwood cultivars have showy bracts in spring, brilliant red foliage in fall, distinct red berries into winter, and graceful year-round architecture that has earned them a reputation for four-season appeal (Cappiello and Shadow 2005). Cornus florida has achieved the status of state flower or tree in North Carolina, Virginia, and Missouri (Missouri Botanical Garden 2023; NC State Extension 2023). In 2019, cultivars of flowering dogwood ranked third in value for deciduous flowering trees in the U.S. and generated more than $31 million in wholesale and retail sales from 1.2 million trees. Tennessee leads the United States in the number of dogwood plants sold, selling almost twice the number of trees as Oregon, the state ranked second in the country (US Department of Agriculture National Agriculture Statistics Service 2020).
Although flowering dogwoods are well known for their year-round appeal, they are best recognized for their spring display of inflorescences where the large white to pink to red “floral” bracts subtend a collection of 20 to 30 small, less conspicuous flowers. The bracts are commonly referred to as petals but are modified leaves (Cappiello and Shadow 2005). The ornamental interest of C. florida also extends to the developing leaves, which vary in color by cultivar. Some leaves are various shades of green, whereas others have either red-pigmented, some degree of red pigment, or variegated leaves. The pink and red colors in the vegetative tissues of dogwoods are a result of anthocyanin biosynthesis (Wadl et al. 2011).
Cornus florida is native to eastern North America and ranges from Massachusetts to Florida and northwest into Ontario, Canada, and south to Texas (Little 1979). In addition to being a significant ornamental species, this understory tree also plays a large ecological role, especially with calcium in the soils of forest habitats. Cornus florida leaves and fruits are high in calcium, making the leaves especially important for the calcium cycle in forests (Thomas 1969) and landscapes. Flowering dogwood fruits are small, single-seeded (occasionally dual-seeded) drupes that develop in clusters of up to 12 on the inflorescence disc and range in color from orange to red. In addition to a high concentration of calcium, the fruits also contain abundant fats and proteins, which makes them an important source of nutrients for wildlife (Halls 1977). Various mammals and birds feed on the berries of C. florida and use the trees as habitat (Eyde 1988; Stiles 1980). Pollination is affected by a variety of insects, but the main groups are andrenid and halictid bees as well as cerambycid beetles (Rhoades et al. 2011).
Cornus florida blooms in late March/early April in the southern United States with its leaves emerging either shortly before or after or concurrently with flowering depending on the location and cultivar. Flowering is affected by physical location of the tree and is considerably delayed in the northern United States and Canada compared with the southern United States. The bracts vary from round to narrowly ovate to cordate and cover the true flowers throughout the winter. The timing of flowering depends on air temperature (De La Pascua et al. 2020; Reader 1975), making the early emerging bracts of C. florida susceptible to frost damage and subsequent infection by Elsinoe cornii Jenkins and Bitanc. (spot anthracnose). This malady causes the bract tissues to produce red-purple lesions, which cause only cosmetic damage and presents no future consequences for the tree.
Pests and diseases have plagued C. florida in the past few decades. The main pest of C. florida is the common dogwood borer (Syanthedon scitula) but can largely be mitigated with cultural techniques (Fulcher et al. 2012). The emergence of dogwood anthracnose (caused by Discula destructiva Redlin) in the mid-1970s devastated natural populations of C. florida, especially in the cooler climates and mountains of the eastern United States (Hadziabdic et al. 2010; Pais et al. 2020; Redlin 1991). However, dogwood anthracnose has not been a major concern for nursery production in recent years (Fulcher et al. 2012) because of prophylactic chemical control measures, lack of conducive environments (cool, wet, and shady) for disease development in the nurseries, and the introduction of the only anthracnose resistant cultivar, ‘Appalachian Spring’ (Windham et al. 1998). Furthermore, many locations with a favorable environment for disease development now lack dogwoods. The primary disease problem with C. florida for the nursery industry as well as homeowners and the landscape industry is the annual epidemic of powdery mildew caused by Erysiphe pulchra (Cooke and Peck) U. Braun and S. Takam (Klein et al. 1998; Li et al. 2009; Windham et al. 2005). This disease emerged in the United States in approximately 1994 and, although not fatal to trees, caused the destruction (unsalable) of tens of millions of dogwoods in production at the time. The presence of powdery mildew has caused the management costs of dogwoods to skyrocket from only $120/ha/year to $1975/ha/year (Li et al. 2009). The Appalachian Series of C. florida including ‘Appalachian Joy’ (PP 18,238 P2) (Trigiano et al. 2016), ‘Jean’s Appalachian Snow’ (13,099 P2), ‘Karen’s Appalachian Blush’ (13,165 P2) and ‘Kay’s Appalachian Mist’ (13,098 P2) (Windham et al. 2003) and ‘Erica’s Appalachian Sunrise’ (unpublished, 2020; PP32468) are resistant to powdery mildew and have somewhat mitigated the higher cost of production.
Origin and Description of ‘Rebecca’s Appalachian Angel’
All flowering dogwoods released by the University of Tennessee are members of the ‘Appalachian’ series. ‘Rebecca’s Appalachian Angel’ was found in Apr 2018 as a solitary tree growing on a steep bank along a bike/walking path in Alcoa, TN, USA. It had three main shoots, probably because of mowing activity, that were each ∼10 to 12 feet (3 to 4 m) in height and with smooth, dark gray bark (N187B). Subsequent measurements are reported as the mean of 20 samples, and colors were compared with the panels in the Royal Horticultural Society (2001) Color Chart. The tree was very noticeable because many of the leaves were very large and measured up to 8 inches (20 cm) in length and 5 inches (13 cm) wide (Fig. 1A and B). Most leaves had a very pronounced yellowish midvein (154B), whereas the remainder of the immature leaf was green-yellow (1B) eventually becoming dark green (140A) when mature and fully expanded. Some spot anthracnose and other spots of unknown causes were present on the leaves throughout the growing season (Fig. 2A). Dogwood anthracnose and powdery mildew were not observed in any of the four growing seasons (years), which could be a consequence of no other dogwoods growing nearby or lack of inoculum. Closed flower buds were yellow-green (144C) to green (N144B) (Fig. 2A) and when open revealed a mean of 26 flowers per inflorescence. The pedicle had a mean length of 1.3 inches (3.4 cm). Anthers were yellow-orange (3B). A mean of four deep red (60A) mature fruits (drupes) per inflorescence were formed by late summer and fall.
Leaves of Cornus florida ‘Rebecca’s Appalachian Angel’. (A) Large and smaller leaves on the same tree. (B) Large detached leaves. Black line = ∼8 inches or 20 cm.
Citation: HortScience 58, 8; 10.21273/HORTSCI17234-23
Flower buds and inflorescences of Cornus florida ‘Rebecca’s Appalachian Angel’. (A) Flower buds. Black arrows indicate possible diseased tissue. (B) Cluster of inflorescences and not fully expanded leaves. (C) Various sizes of fully expanded inflorescences. (D) Large inflorescence composed of cordate-shaped, nonoverlapping bracts. Gray line = ∼3 inches or 8 cm.
Citation: HortScience 58, 8; 10.21273/HORTSCI17234-23
Along with its unusually large leaves for a flowering dogwood cultivar, some inflorescences of ‘Rebecca’s Appalachian Angel’ have very large bracts (Fig. 2B–D). With these, the superior cordate-shaped bracts averaged ∼2.5 inches (6.5 cm) long and 2.2 inches (6.5 cm) across the apex, whereas the inferior cordate-shaped bracts averaged 2.2 inches (5.7 cm) in length and 1.8 inches (4.4 cm) wide. The longest dimension of the inflorescence including the floral disk (Fig. 2C) was ∼5.8 inches (14.7 cm), whereas the shortest was ∼2.5 inches (6.3 cm) in length and 2.3 inches (6.0 cm) wide. The apex of the pure white (no color number) bracts were notched (elongated semicircle or ‘teardrop’) (Fig. 2D) and some tissue around the notch had some faded red-purple (61 C) color on the upper surface but was more pronounced and richer on the bottom surface of the bracts. Color intensity varied with the year. Bracts were very thin and floppy and moved in the slightest breeze, which reminded the authors of angel wings, hence the name of the cultivar.
Hundreds of axillary buds from the original tree in Aloca, TN, were harvested in 2019, 2020, 2021, and 2022, and graphed onto native C. florida rootstocks in September at Hidden Hollow Nursery, Belvidere, TN, USA, and Walnut Hill Farms, Belvidere, TN, USA. Graphed trees grew well with a strong central leader and produced leaves characteristic of ‘Rebecca’s Appalachian Angel’. Thirty-one dormant 36- to 48-inch bareroot trees were potted at the University of Tennessee in early March 2023, maintained in a greenhouse, and later transferred to a bowhouse. All trees produced large leaves that are characteristic of this cultivar. A few flower buds were present on the trees, and some had the large bracts described earlier, which is also typical of ‘Rebecca’s Appalachian Angel’. The nursery producers did not observe powdery mildew on the clones, and it was not detected at the University of Tennessee. However, no claim powdery mildew resistance for ‘Rebecca’s Appalachian Angel’ is made because this will require more extensive trials and observations.
Genetic Characterization of ‘Rebecca’s Appalachian Angel’
Genomic DNA from two independent leaf samples of ‘Rebecca’s Appalachian Angel’, ‘Appalachian Spring’, ‘Jean’s Appalachian Snow’, and ‘Karen’s Appalachian Blush’ and one sample of each ‘Kay’s Appalachian Mist’, ‘Erica’s Appalachian Sunrise’, and ‘Cherokee Brave’ were isolated. The DNA from each sample was amplified using polymerase chain reaction using the primers listed in Table 1 and products identified in Table 2 according to the methods listed in Wadl et al. (2008) and Wang et al. (2009). Duplicate samples of some cultivars were included to assess reproducibility of the amplification process and provided consistent and faithful results (Table 2). Using the information in Table 2, a “decision tree” scheme was developed to identify some of the cultivars in the evaluation and specifically ‘Rebecca’s Appalachian Angel’ (Fig. 3). Additionally, ‘Rebecca’s Appalachian Angel’ also could be identified among this group of arbitrarily selected cultivars with unique products amplified by the primer CF 585.
Simple sequence repeat locus codes, Genbank accession numbers, primer sequences, repeat motifs, and expected bps of products.
Characterization of Cornus florida cultivars using simple sequence repeats (SSRs).
Diagrammatic scheme using simple sequence repeats (SSRs) for identification of Cornus florida cultivars. In the larger boxes, A = ‘Appalachian’ and C = ‘Cherokee’. Numbers are SSR base pair products. Letters and numbers in the smaller boxes represent SSR primer codes (Table 1). ‘Rebecca’s Appalachian Angel’ is distinguished from the other cultivars in the study using the following three SSR primers: CF48, CF585, and CF597.
Citation: HortScience 58, 8; 10.21273/HORTSCI17234-23
‘Rebecca’s Appalachian Angel’ cannot be patented because it was discovered growing wild in an uncultivated area. However, all C. florida cultivars released by the University of Tennessee have “Appalachian” as part of the designated cultivar name and are typically prefaced with a person’s name. The novelty of ‘Rebecca’s Appalachian Angel’ is its large, white bracts and leaves. For more information contact R.N. Trigiano (rtrigian@utk.edu).
References Cited
Call A, Sun Y-X, Pearman PB, Thomas DT, Trigiano RN, Carbone I, Xiang QY. 2016. Genetic structure and post-glacial expansion of Cornus florida L. (Cornaceae): Integrative evidence from phylogeography, population demographic history, and species distribution modeling. J Syst Evol. 54(2):136–151. https://doi.org/10.1111/jse.12171.
Cappiello P, Shadow D. 2005. Dogwoods: The genus Cornus. Timber Press, Portland, OR, USA.
De La Pascua DR, Smith‐Winterscheidt C, Dowell JA, Goolsby EW, Mason CM. 2020. Evolutionary trade‐offs in the chemical defense of floral and fruit tissues across genus Cornus. Am J Bot. 107(9):1260–1273. https://doi.org/10.1002/ajb2.1540.
Eyde RH. 1988. Comprehending Cornus: Puzzles and progress in the systematics of the dogwoods. Bot Rev. 54:233–351. https://doi.org/10.1007/BF02868985.
Fulcher A, Hale F, Windham A. 2012. Dogwood—Cornus spp. IPM for Select Deciduous Trees in Southeastern US Nursery Production. Southern Nursery IPM Working Group.
Hadziabdic D, Fitzpatrick BM, Wang X, Wadl PA, Rinehart TA, Ownley BH, Windham MT, Trigiano RN. 2010. Analysis of genetic diversity in flowering dogwood natural stands using microsatellites: The effects of dogwood anthracnose. Genetica. 138(9–10):1047–1057. https://doi.org/10.1007/s10709-010-9490-8.
Halls LK. 1977. Southern fruit-producing woody plants used by wildlife. Department of Agriculture, Forest Service, Southern Forest Experiment Station.
Klein LA, Windham MT, Trigiano RN. 1998. Natural occurrence of Microsphaera pulchra and Phyllactinia guttata on two Cornus species. Plant Dis. 82(4):383–385. https://doi.org/10.1094/PDIS.1998.82.4.383.
Li Y, Mmbaga MT, Windham AS, Windham MT, Trigiano RN. 2009. Powdery mildew of dogwoods: Current status and future prospects. Plant Dis. 93(11):1084–1092. https://doi.org/10.1094/PDIS-93-11-1084.
Little EL. 1979. Checklist of United States trees: Native and naturalized. Washington, DC, USA.
Mantooth K, Hadziabdic D, Boggess S, Windham M, Miller S, Cai G, Spatafora J, Zhang N, Staton M, Ownley B, Trigiano R. 2017. Confirmation of independent introductions of an exotic plant pathogen of Cornus species, Discula destructiva, on the east and west coasts of North America. PLoS One. 12(7):e0180345. https://doi.org/10.1371/journal.pone.0180345.
Missouri Botanical Garden. 2023. Cornus florida. https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c280. [accessed 22 Apr 2023].
NC State Extension. 2023. Cornus florida. N. C. Ext. Gardner Plant Toolbox. https://plants.ces.ncsu.edu/plants/cornus-florida/. [accessed 22 Apr 2023].
Pais AL, Whetten RW, Xiang Q (Jenny). 2020. Population structure, landscape genomics, and genetic signatures of adaptation to exotic disease pressure in Cornus florida L.—Insights from GWAS and GBS data. J Syst Evol. 58(5):546–570. https://doi.org/10.1111/jse.12592.
Reader RJ. 1975. Effect of air temperature on the flowering date of dogwood (Cornus florida). Can J Bot. 53(15):1523–1534. https://doi.org/10.1139/b75-183.
Redlin SC. 1991. Discula destructiva sp. nov., cause of dogwood anthracnose. Mycologia. 85(5):633–642. https://doi.org/10.1080/00275514.1991.12026062.
Rhoades PR, Klingeman WE, Trigiano RN, Skinner JA. 2011. Evaluating pollination biology of Cornus florida L. and C. kousa (Buerger ex. Miq.) Hance (Cornaceae: Cornales). J Kans Entomol Soc. 84(4):285–297. https://doi.org/10.2317/JKES110418.1.
Stiles EW. 1980. Patterns of fruit presentation and seed dispersal in bird-disseminated woody plants in the eastern deciduous forest. Am Nat. 116(5):670–688. https://doi.org/10.1086/283657.
The Royal Horticulture Society. 2001. The Royal Horticulture Society Colour Chart. London, UK.
Thomas WA. 1969. Accumulation and cycling of calcium by dogwood trees. Ecol Monogr. 39(2):101–120. https://doi.org/10.2307/1950739.
Trigiano RN, Windham AS, Windham M, Wadl PA. 2016. ‘Appalachian Joy’ is a supernumerary, white-bracted cultivar of flowering dogwood (Cornus florida) resistant to powdery mildew (Erysiphe pulchra). HortScience. 51(5):592–594. https://doi.org/10.21273/HORTSCI.51.5.592.
US Department of Agriculture National Agriculture Statistics Service. 2020. Census of Horticulture Specialties. Washington, DC, USA
Wadl PA, Saxton AM, Wang X, Pantalone VR, Rinehart TA, Trigiano RN. 2011. Quantitative trait loci associated with red foliage in Cornus florida L. Mol Breed. 27(3):409–416. https://doi.org/10.1007/s11032-011-9551-4.
Wadl PA, Wang X, Trigiano AN, Skinner JA, Windham MT, Trigiano RN, Rinehart TA, Reed SM, Pantalone VR. 2008. Molecular identification keys for cultivars and lines of Cornus florida and C. kousa based on simple sequence repeat loci. J Am Soc Hortic Sci. 133(6):783–793. https://doi.org/10.21273/JASHS.133.6.783.
Wang X, Wadl PA, Rinehart TA, Scheffler BE, Windham MT, Spiers JM, Johnson DH, Trigiano RN. 2009. A linkage map for flowering dogwood (Cornus florida L.) based on microsatellite markers. Euphytica. 165(1):165–175. https://doi.org/10.1007/s10681-008-9802-6.
Windham MT, Graham ET, Witte WT, Knighten JL, Trigiano RN. 1998. Cornus florida ‘Appalachian Spring’: A white flowering dogwood resistant to dogwood anthracnose. HortScience. 33(7):1265–1267. https://doi.org/10.21273/HORTSCI.33.7.1265.
Windham MT, Trigiano RN, Windham AS. 2005. Susceptibility of Cornus species to two genera of powdery mildew. J Environ Hortic. 23(4):190–192. https://doi.org/10.24266/0738-2898-23.4.190.
Windham MT, Witte WT, Trigiano RN. 2003. Three white-bracted cultivars of Cornus florida resistant to powdery mildew. HortScience. 38(6):1253–1255. https://doi.org/10.21273/HORTSCI.49.9.1230.
