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Cornus alternifolla L.f. Alternate-leaf dogwood

Also known as: Pagoda dogwood, blue dogwood.

Flower clusters at blooming stage; note their upeard orientation

Habitat

Alternate-leaf dogwood grows in the understorey of open mixed woodland, along streams, in margins of forest areas, and in hedges, on fertile, reasonably well-drained soils, often on lower slopes. It tolerates some shade, but requires good light conditions to grow well.

Small irregular-shaped tree, 5m tall

Form

Alternate-leaf dogwood is a large, straggly shrub or small irregular tree that can reach heights of up to 8 m and stem diameters of up to 15 cm. The crown is irregular and often made up of attractive, horizontal tiers of branches that carry many short, upwardly growing shoots on which foliage tends to be clustered, but oriented outwards with upper leaf surfaces mostly flat. The pattern of shoot extension is unique for this region, in that the longer shoots arise in a neoformed manner as branches from the shorter segments. Dead branches may occur throughout the crown.

Expanding leaves below developing flower clusters at the bud stage

Morphology

The leaves are deciduous, simple, dark green above and whitish below, and are borne alternately along the more vigorous shoots, and closer together and sometimes oppositely in pairs, or whorled, near the ends of shoots, especially shorter ones. Each leaf is 4–12 cm long, ovate and widest near the middle, tapered to a long-pointed tip, and to a rounded to wedge-shaped base supported by a petiole about half as long as the blade. The secondary veins curve outwards and forward to follow the smooth, wavy, leaf margin towards the leaf tip.

Twigs with long aylleptic segments

The twigs are shiny, greenish red, to purplish red or dark reddish brown, and angled distinctly where the neoformed longer segments diverge from the short segments.

Twigs with long aylleptic segments

The buds, most of which are terminal buds, are small, pointed, with two or three purplish scales, the outer one appearing loose.

The cream to white flowers are borne in multibranched, rounded, but flat-topped, clusters at the tips of new leafy shoots. Because only some of the flowers in each cluster go on to form fruits, and the other ones drop off, the clusters of fruit are less dense, and the jointed reddish stems that support them show up more. The fruits are berry-like drupes, 8–10 mm across, and dark blue or bluish-black when ripe in late summer.

The bark, when young, is thin, dark olive green to reddish or purplish brown with thin, pale brown, mostly vertical fissures. With increasing age, the fissures deepen and broaden and become separate greyish-brown, flattish ridges.

Ripe fruits in a pinkish-red-stemmed cluster

Notes

The wood of alternate-leaf dogwood is diffuse porous, heavy, and hard. It resists abrasion, and has no commercial value, but may find local use in wooden bearings and slides.

The other dogwood shrub species can be distinguished from the alternate-leaf dogwood by means of the opposite arrangement of their leaves and lateral buds, and opposite branching. The leaves of glossy blackthorn (Rhamnus frangula L.), a vigorously naturalizing and spreading European species, are somewhat similar to those of alternate-leaf dogwood. However, that species is readily identified by its greenish- white flowers and its fruits that change from green to black as they ripen, and are borne on short side stalks along many of its leafy branches.

Bark of a old stem, 4 cm in diameter

Bark of a young stem, 2 cm in diameter