Cornus L.
Current research on Cornus and related genera is summarised on the following webpage: http://www4.ncsu.edu/~qyxiang/.
Cornus, as here circumscribed, is a genus of ca. 45-65 species, mostly native to the northern hemisphere. Two species are native in Belgium as well: Cornus mas L. and C. sanguinea (subsp. sanguinea).
The generic delimitation of Cornus is critical. Some authors have subdivided the genus in several genera, viz Swida Opiz, Thelycrania (Dum.) Fourr., … However, recent molecular phylogenetic studies show that Cornus s.l. is monophyletic and better accepted as a whole (Xiang & al. 2006).
Cornus is popular in cultivation. Wann (1997) enumerates 27 species that are cultivated as ornamentals in Europe. Further useful information is provided by Schulz (2011).
1. Inflorescence appearing before the leaves. Petals yellow, with an involucre of petal-like bracts. Fruit red, 12-15 mm long. Twigs usually green in winter (native) === Cornus mas
1. Inflorescence appearing after the leaves. Petals whitish, involucre of petal-like bracts absent. Fruit purplish-black or whitish, 4-8 mm long. Twigs usually red in winter === 2
2. Fruit purplish-black. Petals 4-7 mm long. Largest leaves usually with 3-4(-5) lateral veins, lower side not conspicuously paler than upper side === 1. Cornus sanguinea
2. Fruit whitish (sometimes slightly tinged blue). Petals 3-4 mm long. Largest leaves usually with (5-) 6-7 lateral veins, lower side conspicuously paler than upper side === 2. C. sericea
Literature
Cappiello P. & Shadow D. (2005) Dogwoods. Timber Press, Portland: 224 p.
De Jong P.C. & Ilsink L.K.J. (1995) Cornus (Kornoelje). Dendroflora 32: 27-36.
Diekmann F.-H. & Spethmann W. (1997) Monographie der Gattung Cornus. Wissenschaftliche Gehölzmonographien 3. Hausmann Verlag: 112 p.
Eyde R.H. (1988) Comprehending Cornus: puzzles and progress in the systematics of the dogwoods. Bot. Rev. 54(3): 233-351.
Gayraud A. (2013) A monograph of the genus Cornus. Pistoia, Giorgio Tesi Editrice: 222 p.
Goetghebeur P. (1999) Morfologie en systematiek van het genus Cornus L. Belg. Dendrol. Belge 1998: 51-79.
Houtman R.T. & Hoffman M.H.A. (2008) Winterkornoeljes - sortimentsonderzoek en keuringsrapport. Dendroflora 45: 47-75.
Murrell Z.E. (1993) Phylogenetic relationships in Cornus (Cornaceae). Syst. Bot. 18: 469-495.
Roloff A. & Bärtels A. (2006) Flora der Gehölze (2e Auflage). Ulmer, Stuttgart: 844 p.
Schulz B. (2011) Die Gattung Cornus (Cornaceae), Hartriegel und Kornelkirsche, Teile 1 und 2. Teil 1: Übersicht über die Gattung. Teil 2: Die Wechselständigen Hartriegel Cornus alternifolia L.f. 1782 und Cornus controversa Hemsley 1909. Mitt. Deutsch. Dendrol. Gesel. 96: 67-83.
Schulz B. (2012) Die Gattung Cornus (Cornaceae), Hartriegel und Kornelkirsche, Teil 3: Die Kleinfrüchtigen Hartriegel (Untergattung Kraniopsis). Mitt. Deutsch. Dendrol. Gesel. 97: 91-132.
Wann J.D. (1997) Cornus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 362-366.
Xiang Q.-Y., Thomas D.T., Zhang W., Manchester S.R. & Murrell Z. (2006) Species level phylogeny of the Dogwood genus Cornus (Cornaceae) based on molecular and morphological evidence– implication in taxonomy and Tertiary intercontinental migration. Taxon 55: 9-30.