Cornus x elwinortonii Mattera, T. Molnar, & Struwe, 2015

Mattera, Robert, Molnar, Thomas & Struwe, Lena, 2015, Cornus x elwinortonii and Cornus x rutgersensis (Cornaceae), new names for two artificially produced hybrids of big-bracted dogwoods, PhytoKeys 55, pp. 93-111 : 96-97

Cornus x elwinortonii Mattera, T. Molnar, & Struwe hybr. nov. Orton’s dogwood Figs 1, 2

Diagnosis.

Cornus x elwinortonii is similar to both Cornus kousa and Cornus nuttallii but differs in its intermediate flower number per inflorescence and in its intermediate tree height. Cornus x elwinortonii has 55-80 flowers per head, whereas Cornus kousa has 20-60, and Cornus nuttallii has 70-100. Cornus x elwinortonii is also intermediate in plant height, with a maximum of 10 m height ( Cornus kousa reaches 6 m height, while Cornus nuttallii is 12-23 m tall as a mature tree).

Type.

USA. New Jersey: New Brunswick, Middlesex County, Ryders Lane, Horticultural Farm 1, original tree (ramet) of ‘KN4-43’ Starlight®, cultivated plant in open field adjacent to Rutgers Equine research farm, surrounded by hazelnut ( Corylus spp.) trees planted in rows, GPS location (WGS84) 40.4676N, -74.4281E, 18 m, 17 May 2014, R. Mattera 33 (holotype: NY, isotypes: CHR, JEPS, MO, US, to be distributed).

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, fine, 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 inflorescence buds not covered by the two outer opposing pairs of vegetative bracts, minimally covered by two inner opposing pairs of floral bracts (0-40% coverage; floral bracts more developed than in Cornus kousa during overwintering). Inflorescence capitate, globose, with 55-80 sessile flowers 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 flowering. 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; filaments 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.

Parent source material.

The parents of the F1 hybrid ( ‘KN4-43’ Starlight®) are Cornus kousa 'Simpson No. 1' (female), an unpatented cultivar received from Tennessee Valley Nursery (Winchester, TN, USA) and planted at Rutgers Gardens (New Brunswick, NJ) on 16 April 1970, and Cornus nuttallii ‘Goldspot’ (male), received from Alfred Teufel Nursery (Portland, OR, USA) and planted in 1972.

Ecology and phenology.

In New Jersey, Cornus x elwinortonii flowers during May and June, and the fruit matures from September to October. Various beetles and bees visit the flowers at anthesis, with an abundance of goldenrod soldier beetles ( Chauliognathus pensylvanicus ) frequently observed by the authors. The mostly sterile fruit with little pulp generally senesces and falls from the trees by October. The few fruits with a developing seed are swollen and have more pulp. We suspect they are eaten by insects and birds.

Etymology.

The 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 first to successfully develop and release a hybrid between Cornus kousa and Cornus nuttallii . The common name, Orton’s dogwood, is proposed for this hybrid.

Distribution.

Cornus x elwinortonii is known only from cultivation, although at times it produces viable seeds. The natural range of the staminate parent, Cornus 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). The other parent, Cornus kousa , is native to mesic forests of Japan, Korea and China (Flint 1997, Xiang and Boufford 2005). Cornus nuttallii cannot withstand sustained periods of frost, thus limiting its natural and cultivated range. In contrast, Cornus 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). The hybrid Cornus x elwinortonii can survive sustained frosts and has a similar climate range as Cornus kousa . However, for some cultivars of Cornus x elwinortonii the floral buds are less cold hardy than in the parent Cornus kousa . In colder climates, includ ing in New Brunswick, NJ, where the hybrid originated, flower buds can be damaged by cold winter temperatures, leading to a reduced floral bract display in the spring (E. Orton personal communication).

Horticulture.

Plants of Cornus x elwinortonii are grown as landscape ornamentals and can be cultivated wherever Cornus kousa , Cornus nuttallii , and Cornus florida may be grown. This hybrid is cultivated for its all-year round appeal: floral bracts, attractive foliage, autumn color and appealing bark ( Eberts 2007) Cornus x elwinortonii is typically propagated asexually through budding and grafting on seedling rootstocks of Cornus kousa or Cornus florida . Patented and trademarked cultivars that belong to this hybrid include ‘KN4-43’ Starlight® (F1), 'KN 30-8' Venus® (first backcross to Cornus kousa ), and ‘KN144-2’ Rosy Teacups® (third serial backcross to Cornus kousa ; Table 1 ). We know of no other commercially available cultivars of Cornus x elwinortonii .

Disease response.

While dogwood anthracnose caused by the fungus Discula destructiva Redlin is known to infect and kill Cornus nuttallii , it has not been reported to be a significant problem on either Cornus kousa or Cornus x elwinortonii ( Daughtrey and Hibben 1994; Fulcher et al. 2012; Hagan et al. 1998).

Additional material provided.

Additional collections from the same individual as the holotype specimen, but on different dates (R. Mattera 27, R. Mattera 29, R. Mattera 31, and R. Mattera 35) will all be deposited at CHR, NY, and MO).