Oxydendrum arboreum (L.) DC.
Ericaceae -- Heath family
Ronald P. Overton
Sourwood (Oxydendrum arboreum) grows in the upland forests of the southeastern United States. Also known as sorrel-tree or lily-of-the-valley-tree, its flowers are an important source of honey in some areas but it is of little value as a timber species. Sourwood sprouts often interfere with the establishment of more desirable species in second-growth and cutover areas. This mid-summer flowering tree is an attractive ornamental.
Sourwood is found from southwest Pennsylvania to southern Ohio, and southern Indiana, south to southeastern Louisiana and the coastal region of Mississippi, Alabama, and northwest Florida; west to western Kentucky and Tennessee, and to the Delta in Mississippi; and east to the Atlantic coast from southern Virginia to central North Carolina, and to the edge of the Coastal Plain in South Carolina and Georgia. The main range lies between latitude 30° and 40° N. and longitude 75° and 92° W. Sourwood reaches its largest size on the western slopes of the Great Smoky Mountains in Tennessee.
-The native range of sourwood.
Annual precipitation within the range of sourwood varies from 1020 mm (40 in) in the North to 2030 mm (80 in) in the central Appalachians. Warm season precipitation ranges from 530 mm (21 in) in the North to 910 mm. (36 in) on the gulf coast and in the Appalachians, and annual snowfall varies from none along the gulf coast to 152 cm (60 in) in the Appalachians. The length of the growing season fluctuates from 150 days in the mountains of southern Pennsylvania to 300 days in northern Florida. Temperature extremes vary from -29° C (-20° F) to 42° C (107° F) within the range of sourwood.
In the central Appalachians sourwood is most abundant on subxeric open slopes and ridges occupied by chestnut oak (Quercus prinus), white oak (Q. alba), scarlet oak (Q. coccinea), and Virginia pine (Pinus virginiana). It appears less frequently on more mesic sites such as coves and sheltered slopes (17). Throughout this area sourwood is found up to 1520 m (5,000 ft) but rarely to 1710 m (5,600 ft) (13).
Sourwood grows throughout the Piedmont uplands. It is also found along Piedmont streams on well-drained lowland areas not subject to ordinary flooding (10). Where it enters the Coastal Plain it is found on the gently rolling areas of the upper portion; toward the coast it is restricted to old dunes and well-drained slopes and ridges above streams and swamp borders.
Like most of the Ericaceae, sourwood generally does not grow on soils of limestone origin (8,11) but is most commonly found growing on soils in the orders Ultisols, Inceptisols, and Entisols.
Sourwood is an understory to midcanopy associate of the following forest cover types (Society of American Foresters) (6):
40 Post Oak-Blackjack Oak
44 Chestnut Oak
51 White Pine-Chestnut Oak
52 White Oak-Black Oak-Northern Red Oak
53 White Oak
75 Shortleaf Pine
76 Shortleaf Pine-Oak
78 Virginia Pine-Oak
79 Virginia Pine
81 Loblolly Pine
82 Loblolly Pine-Hardwood
110 Black Oak
Other associates, in addition to the cover type species, are sweetgum (Liquidambar styraciflua); yellow-poplar (Liriodendron tulipifera); scarlet and southern red oak (Q. falcata); red and sugar maple (Acer rubrum and A. saccharum); shagbark, bitternut, pignut, and mockernut hickory (Carya ovata, C. cordiformis, C. glabra, and C. tomentosa); white ash (Fraxinus americana); American beech (Fagus grandifolia); eastern hemlock (Tsuga canadensis); flowering dogwood (Cornus florida); sassafras (Sassafras albidum); American hornbeam (Carpinus caroliniana); eastern hophornbeam (Ostrya virginiana); and redbud (Cercis canadensis).
Flowering and Fruiting- Sourwood is among the latest of the flowering shrubs and trees to bloom, The white, bell-shaped perfect flowers appear from late June to August in copious masses on one-sided racemes clustered in an open particle. The flowers are insect pollinated and are an important honey source in some areas (14).
Seed Production and Dissemination- The fruit is a capsule 6 to 13 min (0.25 to 0.5 in) in length. It ripens in September and October, and the tiny seeds are dispersed gradually throughout the winter by the dehiscing capsule. The number of seeds in clean lots range from 4 080 000 to 12 125 000 seeds per kilogram (1,850,000 to 5,500,000/lb) (14).
Seedling Development- Seedbed requirements are not known for natural regeneration. In the Piedmont, however, sourwood seedlings and saplings are found in all stages of succession from young pine stands to the oak-hickory climax (10). This indicates that seed germination and establishment may occur on litter and under partially shaded conditions.
Techniques have been described for sourwood seed collection, storage, and germination (2,5,14). Acid sandy peat is recommended as a seedbed for sourwood. Germination is epigeal.
Vegetative Reproduction- Sourwood sprouts prolifically and persistently from the stump and often must be treated with herbicides to release more desirable species in second growth and in cutover areas (7,9,12,15). Sourwood is difficult to propagate from cuttings. A single report found softwood cuttings (short side shoots), made with a heel and taken in late July with a 90 ppm IBA soak, rooted 80 percent when placed in a sand:peat (equal volumes) mix under mist (5). No reports were found of propagation by grafting.
Growth and Yield- The maximum size for sourwood is 24 in (80 ft) in height and 61 cm (24 in) in diameter. It is typically much smaller, reaching 6 to 15 in (20 to 50 ft) in height and 20 to 30 cm (8 to 1 in) in diameter (11).
Sourwood usually remains in the forest understory from seedling to maturity. It occasionally enters the overstory in Piedmont lowland pine stands, but on upland sites it attains the upper canopy only if some disturbance removes the overtopping vegetation (10)
Sourwood develops a slender trunk and small crown in dense stands. In more open situations it forms a short, often leaning trunk dividing into several stout, ascending limbs. Growth is slow in established stands, but the initial growth of sprout in cutover areas is rapid enough to hinder establishment of more desirable species (7,12). Per-acre volume estimates are not available for this specie because it usually grows in mixture with other species rather than in pure stands.
Rooting Habit- No information is currently available on the rooting habit of sourwood.
Reaction to Competition- Sourwood is classed as tolerant of shade and can grow and reproduce in the understory of climax (oak-hickory) forest (3,10,11). Its response to release is not definitely known but is thought to be poor.
Damaging Agents- Several insects attack sour wood but normally do no serious harm (1). The dog. wood-twig borer, Oberea tripunctata, and the twig girdler, Oncideres cingulata, attack the twigs; the fall webworm, Hyphantria cunea (7), and the hickory horned devil (the larva of the regal moth), Citheronia regalis, attack the foliage.
There are no known reports of serious diseases that affect sourwood.
Sourwood is occasionally used as an ornamental because of its brilliant fall color and midsummer flowers (7). It is of little value as a timber species the wood is heavy and is used locally for handles and fuel and in mixture with other species for pulp (8). Sourwood is important as a source of honey in some areas and sourwood honey is marketed locally.
No studies on the genetic characteristics of sourwood have been reported.