Oxydendrum arboreum, Sourwood, Sorrel tree, titi tree

Oxydendrum arboreum, commonly called sourwood or sorrel tree, is a deciduous understory tree belonging to Ericaceae (Heath family). The plant is native to 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. It is perhaps most commonly found on rocky wooded slopes in the Appalachian Mountains, often growing in combination with other heath family members (e.g., azaleas and rhododendrons) that share the same acidic soil preferences. Some of the popular common names of the plant are Sourwood, Lily-of-the-valley tree, Sorrel tree, common sourwood, titi, titi tree, arrowwood, elk tree, sorrel gum, sour gum and tree Andromeda.

Genus name Oxydendrum comes from the Greek words oxys meaning acid and dendron meaning a tree. The foliage is bitter. Specific epithet arboretum comes from the Latin word arboreus (of a tree). The sour tree name comes from the acidic and bitter-tasting foliage, which is caused by oxalic acid in the leaf tissues. Sourwood is often used as an ornamental for its vivid autumn color. Leaf color ranges from vivid red through salmon, pink, and yellow. Sourwood flowers are attractive to bees, and Sourwood honey is much prized. Sourwood grows best in well-draining acidic soils. Best flowering and fall color occur on plants growing in full sun. Sourwood is often available from nurseries. It can also be grown from seed planted in the autumn, or from cuttings of semi-hardened twigs taken in early summer.

Sourwood Facts

Plant Description

Sourwood is a deciduous, small to medium-sized tree that normally grows about 10–20 m (33–66 ft.) tall with a trunk up to 50 cm (20 in) diameter with a straight, slender trunk and narrow oblong crown. Occasionally on extremely productive sites, this species can reach heights in excess of 30 meters and 60 cm diameter. The plant is found growing in woodlands on free-draining or gravelly acidic soils, on cliff faces, along streams and around the margins of swamps and pine heaths, dry rocky woods, in pine or mixed pine, and hardwood stands, in hardwood forests, and well-drained woodlands of bluffs. The plant prefers moist, organically rich, well-drained soils. It also does best in acidic, clay, loam sand.

Roots

Sourwood roots are developed from a taproot sensing aerated soil depth and throwing out lateral roots behind its tip. This juvenile taproot is soon compartmentalized away from the tree and a mature fibrous root system is sustained. Sourwood has a shallow, high oxygen demanding root system which is not effective with too much interference from other species. Sourwood does not have any significant allopathic impact of its own. Sourwood will sprout effectively from its stump and root crown area.

Bark

Sourwood periderm is unusual among other hardwood tree species. The periderm is shiny grey to reddish-grey-brown on the surface with a reddish-orange inner layer. The periderm is deeply creased with long furrows and short horizontal dividing fissures which yield a rectangular blocky texture (like persimmon). The mature periderm is usually 0.66 to 1.0 inches in thickness.

Twigs

Sourwood twigs are stiff but slender, with a crooked or zigzag growth pattern. First-year twigs are reddish to bronze-colored, while older twigs range from reddish-green to reddish-orange to yellowish-brown in color. Twigs are smooth with conspicuous orange or red-tinted, oblong-shaped, lenticels.

Leaf scars are shield or triangular-shaped and raised above the twig surface, with no associated stipular scars. Each leaf scar has a single C or V-shaped bundle scar. The pith is solid, white-colored, round in cross-section, and has no cross walls. Sourwood is notorious for being extremely difficult to propagate from twig cuttings.

Buds

Sourwood has no true terminal buds. Lateral bud becomes the new shoot leader for each growth flush and each new season. Lateral bud dominance gives twigs a crooked or zig-zag appearance. Lateral buds are sparsely and minutely hairy on bud scale margins and across the inner surface. Lateral buds are small, round or globular shaped, 0.08 to 0.13 inches in diameter, and unstalked. They appear to be partially embedded in the periderm. Buds have 3-6 dark red, rounded scales terminating in a minute point at the bud top.

Leaves

Sourwood leaves are arranged along the twig in an alternate or spiral form. Leaves are simple, thin, deciduous, and oblong-elliptical to oblong-lanceolate in shape. The leaf tip has a long point and the leaf base is wedge-shaped. Leaf margin can be a combination of several forms. The most common margin is finely toothed or finely toothed except near the base. The least common leaf margin is a smooth, untoothed edge. Leaves are sour or bitter to taste. Leaves are 4.5 – 7.5 inches long on average and 1.2 – 3.0 inches wide on average.

The upper leaf surface is shiny, smooth, with a bright yellowish-green to a darker green color, if in full sun, and a yellowish-orange tinted green color under shaded conditions. The leaf underside has a bright yellow mid-rib which has stiff minute hairs (trichomes). These trichomes can occasionally also appear on the upper leaf surface over the midrib. The lower leaf surface is paler green than the upper leaf surface. Leaves are connected to the twig with a 0.66 to 1.0-inch long petiole covered with a few stiff small trichomes. Leaves begin senescence early and generate a bright crimson or purplish-burgundy color in early fall while most other trees are still fully green.

Flowers

Sourwood trees are co-sexual (both male and female parts within each flower) with very noticeable and unique flowering structures. Individual sourwood flowers are small, regular, symmetrically shaped, fragrant, and showy. Individual flowers are bell or urn-shaped with white to creamy-white colored petals. The flowers are waxy, slightly minutely hairy, and small about 0.25 to 0.33 inches long. A number of people compare individual sourwood flowers with the bulb perennial herbaceous flower called “lily of the valley” in form. Petals form five short lobes. Petals are held at their base by sepals which all together form five lobes and stay attached as the fruits ripen. Each flower contains ten stamens.

Flowers are generated after the leaves have already expanded. Numerous small flowers are held on one side of long sweeping or drooping sprays, each spray (raceme) being 5.5 – 10 inches long. The end of the upper branches can produce 3-8 terminal racemes of flowers around the entire crown. Lower branches may generate fewer racemes. Light-colored, flower racemes and their sweeping, elongated growth form, provide a lacy or soft textured appearance to the tree. Flowers are insect-pollinated, primarily by bees, using rich nectar and fragrant smell for attraction. Each flower produces small amounts of pollen. Flowering occurs near the mid-growing season, roughly late May to mid-July across the range. Flowers dangle downward until about ten days after fertilization when the individual flower stems begin to curl upward. The individual flower stems have fine minute trichomes. Flowering normally takes place between June to August.

Fruit

Fertile flowers are followed by small, hard, dry, oval to egg-shaped, yellowish to greenish-grey colored, pointed capsules which can split along five lines on the sides. The capsule is covered with minute hairs and the fruit stands erect on a curved, short, fruit stalk which earlier in the growing season had dangled downward to enable flower fertilization. The capsule is about 0.35 inches long. The capsule ripens by the first of October and remains attached to the tree long after splitting in late fall to release many tiny seeds. Seeds are continually released into winter. Fruit collection should be in late fall. Do not collect any fruit which hangs down. Rub the fruits together to split the capsule and release the seeds.

Seeds

Each capsule holds many minutes, oblong-shaped, pale brown to orange-yellow colored, wingless, 0.125 inch long seeds. Each seed is surrounded by a loose, thin, papery seed coat that looks like two small wings or points. Seeds freshly out of the capsule in late fall have no dormancy requirement and no pretreatment is needed for germination except for having at least four hours of light on the seedbed. Seed production occurs every year with large variability in seed numbers. Expect 2-5 million seeds per pound.

Traditional uses and benefits of Sourwood

• Leaves are cardiac, diuretic, refrigerant and tonic.
• Tea made from the leaves has been used in the treatment of asthma, diarrhea?, and indigestion and to check excessive menstrual bleeding.
• It is a diuretic and is a folk remedy for treating fevers, kidney and bladder ailments.
• Bark has been chewed in the treatment of mouth ulcers.
• Sourwood has been used for millennia for different human ailments.
• Native Americans used leaf infusions for treating menstrual and menopause problems, diarrhea?, lung and breathing problems, and as a sedative for nerves.
• Sap, gum, or inner bark was applied for skin irritation and chewed for mouth sores.
• European Americans used sourwood as a tonic, decoction, pills made from solid tree tissues, and as tincture.
• Sourwood products were used to treat urinary problems (increase urine flow/diuretic), enlarged prostate, bowel troubles, diarrhea?, dysentery, stomach ache, and fever?.
• Sourwood gum was chewed to alleviate thirst and treat mouth sores, and the green bark was rubbed on itchy skin.
• Sourwood whiskey tinctures used in tonics were targeted primarily at men’s urinary tract problems, leg swelling?, and heart problems.
• Leaves can be chewed (but should not be swallowed) to help alleviate a dry-feeling mouth.
• Sourwood tea can also cure fevers, nausea?, and stop excessive menstrual bleeding.
• You can also chew the bark of this tree to treat mouth ulcers and canker sores.
• Herbal tea can be used to alleviate symptoms of asthma, dysentery, diarrhea?, as well as kidney and bladder ailments.
• Sourwood infusions can be used to stop diarrhea?.
• They also made it into a tonic for indigestion, nervousness, asthma and spitting blood.

Culinary Uses

• The youngest new leaves have been used to act as a sorrel green (sour / acidic taste) in salads.
• Young sourwood leaves can be a wonderful addition to salads and stews.
• You can also boil sourwood leaves to make a delicious herbal tea.
• Herbal tea has a zesty flavor that will taste amazing when paired with honey.
• Juice from these flowers is usually used to make sourwood jelly.

Other Facts

• Wood is occasionally used for paneling, tool handles, bearings etc.
• Sourwood is occasionally used as an ornamental because of the brilliant fall color of its leaves and midsummer flowers.
• Flowers of sourwood are also an important source of honey.

References