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The not-so-familiar black walnut

Black walnuts are familiar yet very unusual and valuable trees, and quite rare growing wild around here. At Jordan Lake State Recreation Area’s Seaforth access there are several exceptionally large trees of various kinds, including a black walnut. It’s spreading boughs are shaggy with resurrection ferns, verdant green after rain, contrasting with the yellowish-green of the walnut leaves, and appear dead at other times. The walnut is partially hollow and has dead branches, so it seems precarious and I wonder if the raised water table and/or heavy summer foot traffic is harming it. There are several much younger walnuts nearby. Near UNC’s Friday Center there is a black walnut about 2′ across, with a plaque saying it sprouted circa 1880. Large walnuts line paths at Durham’s West Point on the Eno. There are a few walnuts in the Northeast Creek basin. A tall tree more than a foot across grows at the base of a moist northwest facing slope near tributary Burdens Creek. It is a mystery how it got there. A few miles away there are spindly but nut-producing walnuts growing wild by a road in Chatham County connected only to Durham and Wake.

Their large nuts, classified botanically as drupes, fall around October, later than acorns and hickory nuts. An unusual feature is their smooth, relatively soft, fragrant, yellowish-green changing to black, staining husks, resembling a lemon more than a nut such as a pecan. Last fall there were unusually few walnuts under the Burdens Creek tree, whether because of the drought or because production varies yearly. On the other hand smallish nuts covered the ground under the Chapel Hill tree last October, and squirrels were gathered when I visited.

Black walnuts have dark, regularly furrowed bark and are tall and narrow in forests but short and very broad without competition. Giants can grow to 150′ tall and 6′ across, but walnut wood is valuable, so valuable that trickery and poaching occurs, and many were cut. They have large pinnately compound leaves up to 2′ long and 6” wide, with 9 to 23 long-pointed and serrated leaflets in pairs, smaller at the ends of the leaf, and usually there isn’t a leaflet at the tip. The leaflets have very short stems (petiolules) and the compound leaves alternate along the twigs. There is some hairiness on the underside of the leaflets and the leaf stem, called a rachis. Broken leaves and husks have a distinctive smell, lemony to me. Their leaves turn yellow early, contrasting with the dark trunks.

Several trees have similar leaves. White walnuts or butternuts, native in the Smokies, and introduced here, have oblong nuts, fewer leaflets (but usually with a terminal leaflet), and while both walnuts have chambered pith inside their twigs, it is darker brown in butternuts. Both species have grayish buds and the leaves fall to reveal three-lobed leaf scars, but there is a hairy spot only in butternuts and their buds are elongated. Hickories, such as bitternuts and pecans, are in the walnut family, but typically have fewer leaflets per leaf, a terminal leaflet, buds covered in scales, pith without chambers, and their nuts are usually dehiscent, opening along sutures. Locusts and Ailanthus also have pinnate compound leaves but are often small trees with multiple trunks growing in open areas. Ailanthus have very large leaves and leaf scars, a distinctive smell, and are most common in built-up areas while black locusts are thorny and produce fragrant white pealike flowers in late April.

Black walnuts seem to like well-drained soil and usually grow far from waterways. They grow fast, but are long-lived and don’t like shade, and they have a way to preserve their sunlight.

Black walnuts produce wind-pollinated catkins before leafing, each tree having both sexes. The dangling male catkins are 3 – 5” long. The female flowers are in clusters of 2-5 near the twig tips. The male and female flowers open at different times, but self-pollination is possible. A sapling can produce nuts after only five years, but few until age 10 – 15. The huge nuts are covered in a smooth husk, surrounding a seed with very thick, irregular wooden walls. ‘Everyone’ eats the nuts, yet I often find many left under wild trees and it takes a lot of effort to get inside. Apparently walnuts need a long cold period to sprout, and squirrels can steal planted nuts.

Black walnuts are known botanically as Juglans nigra, the generic name being an abbreviation for Latin Jovis glans, the acorn or nut of Jupiter (it was said people once lived on acorns while the gods ate walnuts). The word walnut originally referred to Persian walnuts, and is supposed to be a combination of the Anglo-Saxon for Welsh or Celtic, signifying foreign, and nut, wealh hnutu, as opposed to hazelnuts. Walnuts are honored in many place names, such as Cary’s Walnut Creek.

An unusual feature of black walnuts is their allelopathy. The walnut near Burdens Creek grows in a mature deciduous forest, but is in a sunnier glade. Around now toothworts and other early wildflowers bloom around it, joined by pink redbuds, an understory tree in the pea family, and in summer other peas cover the ground. Legumes often carpet the ground under walnuts in summer. Black walnuts produce hydrojuglone, which oxidizes into juglone and washes into the soil, to poison competitors, though ash, legumes, etc. seem immune. Some soil bacteria seem to be able to live on juglone.

Despite poisoning other plants, walnuts are edible to many animals. Squirrels, white footed-mice, and chipmunks disperse the nuts. In winter rabbits and deer nibble saplings. On the other hand walnut is harmful to horses and fish. Many insects feed on walnuts, including a curculio weevil, woodboring beetles, the walnut lace bug, stinkbugs, and aphids. Walnut fruitflies are supposed to develop in the husks, but I haven’t seen any. Many lepidopterans consume walnut, including one small butterfly, the banded hairstreak. Moths include gigantic hickory horned devils (caterpillars of the royal or regal walnut moth), related imperial moths, luna moths, walnut caterpillars and other Datanas, monkey slugs, walnut sphinx moths, curved-tooth geometers (a relatively large dark brown moth common at lights around April or May), American dagger moths and relatives, salt marsh caterpillars, fall webworms, walnut shoot moths, and several more.

Walnuts have a lot of versatility for humanity. Nuts are gathered from the ground and the nutmeat can be eaten raw, ground into flour, or boiled for oil used for cooking, fuel, and as polish (butternuts are more famous for oil). The trees can be taped like sugar maples. The husks produce a dye used to color cloth and even hair, and as ink. Walnut is supposed to repeal bedbugs and other insects, and I have wondered if the husks could be used to treat wood. Pulverized nuts are used in abrasives, filters, tires, composted, etc. The beautiful smooth wood was also used in furniture, paneling, veneer, cabinets, carriages, sewing machines, appliances, musical instruments, and for both cradles and caskets. During wars it went for gunstocks and airplane propellers. Walnut resists decay, so it was used for rail fences and railroad ties.

The leaves and husks have been known to cause dermatitis, but there are many herbal uses. The bark was used for toothaches; husks were used for ringworm, external inflammation, and to cause sleep; leaves were used for insect repellant and reportedly for sunscreen; and various parts were used to treat gastrointestinal problems. Juglone could be useful as a sedative and cancer inhibitor.

Thousand canker disease is an emerging threat for walnuts, though still far from here. Unlike other new catastrophic forest maladies like emerald ash borer and laurel wilt, thousand canker disease is native to North America, but was apparently unknown in the East until it reached Knoxville around 2010, so black walnuts still lack resistance. Thousand canker disease is caused by a recently discovered fungus spread by the walnut twig beetle, native in the Southwest and Mexico. In fall 2012 the disease was found in Haywood County, bordering Tennessee, but it is not known to have spread elsewhere in North Carolina since. The disease is present in several Western states, but only four Eastern states. Butternuts are susceptible and also face a canker noticed in 1967, probably from Asia. So walnut is another wood to be careful about moving over distances.

Beautiful hibiscus

This is based on an article I wrote for the July issue of the Parkwood Inside/Out. There were some website issues, so I haven’t posted in a few months. Hibiscus are probably still blooming; they were still in bloom in the Coker Arboretum last week, but it is getting late in the season for them, so now is the time to go to your local pond.

Parkwood Lake Hibiscus

Hibiscus or mallows are the showiest natives growing along the margins of Parkwood Lake and local beaver ponds in midsummer. The most common species is a small bush with soft, dark green leaves and huge white 5-petalled flowers with dark red or purplish centers, each flower lasting one day. I think this is Hibiscus moscheutos, or H. palustris, but they seem to be considered the same species now. The other Hibiscus is a rare species with bright red flowers, probably H. coccineus, native to Georgia, Florida, and Alabama, but apparently introduced in North Carolina relatively recently, since it doesn’t appear in the comprehensive Manual of the Vascular Flora of the Carolinas written in the 60’s. There were some small Hibiscus at the Clermont end of the Lake before it was deepened last year, and I thought they were killed, despite the ribbons I tied on them, but there are still a few small Hibiscus there. They aren’t flowering, possibly because they get too much shade, or they were cut back, or maybe they sprouted recently. Elsewhere in Parkwood there are rose-of-Sharon (H. syriacus), a tree-sized Old World Hibiscus. Hibiscus are in the mallow family (Malvaceae) with marsh mallows (Althea officinalis, a European plant found in North Carolina whose roots were used to make the first marshmallows), okra, hollyhocks, and cotton.

I’m not completely sure what the white Hibiscus are. Both H. moscheutos and H. palustris have been called swamp rose mallows, and the former has also been called wild cotton (but don’t look for a cotton boll), breast root, and crimson-eyed rose-mallow. Both can have pink flowers, but H. moscheutos is usually white and I only see white flowers around here. The name would make more sense if the rose in rose-mallow just means rose-like. The Greek word for mallow is hibiscus and moscheutos refers to the smell of musk roses, another relative. These plants are perennials, but their tough stalks seem to regrow from the base each year. I usually see hibiscus growing around 2 to 4 feet tall, but they can reach 8 feet. They have oval to three pointed, red maple-like leaves alternating along the stalks. The leaves don’t look particularly fuzzy, but they still have a soft texture. The large flower buds are surrounded by an array of needlelike, but soft green bracts and larger sepals that extend after flowering to protect the developing fruit. The petals have a soft, pleated appearance and the male and female parts are united to form a structure like a radio tower jutting from the center, like other Hibiscuses. The flower gives way to a dry capsule that opens in the fall or winter, releasing many seeds. Hibiscus don’t produce fibers, but the fruit resembles an unopened cotton boll. These mallows like to grow in marshes and beside ponds in full sun, but yards with moist soil and those around Parkwood Lake should be able to grow them.

H. coccineus is called rose, scarlet, or brilliant mallow, and scarlet mallow comes closest to describing the color. Supposedly it is also called Texas star, but it shouldn’t grow there naturally. This species can grow up to 10 feet tall and has palmate, or hand-like, leaves with three to five points. There must be some red Hibiscus in yards around the Lake, and they self-seeded into the marshy ground along Clermont, or someone planted them there, because I’ve never seen them naturalized elsewhere. These plants seem more lofty and airy than the white Hibiscus and very tall examples can be seen waving over the flowerbeds along the central brick path at UNC’s Coker Arboretum.

Hibiscus are supposed to attract butterflies and ruby-throated hummingbirds, but I mainly see bees visit them. I also don’t see many insects eating the leaves, but Japanese beetles and the spiny caterpillars of Io moths, one of the smaller giant silk moths, can eat Hibiscus, and common checkered-skippers, painted ladies, and gray hairstreak butterfly caterpillars, eat plants in the mallow family and this might include Hibiscus. Cooks can use Hibiscus leaves as a thickener like okra and as cooked greens. Hibiscus, especially H. moscheutos, leaves and roots are mucilaginous and were used herbally to soothe and soften tissue and H. moscheutos was used against breast cancer.

If you look for Hibiscus at the Lake, you will probably notice the color of the water. At the start of July the Lake was opaque yellow with silt eroded from the Meadows at Southpoint construction site at the corner of 54 and Barbee Road, the headwaters of the stream feeding the Lake. Durham Stormwater Services investigated and said there weren’t any big problems with the erosion controls and the contractor was very cooperative. This is how the Lake fills with muck, but soil also bleeds from yards with every rain and much of Parkwood drains into the Lake, so when people pile leaves and logs in the streams, this is also usually where they are heading. I’m not sure how much of a problem the recent runoff is for aquatic life, but excessive siltiness is harmful for some organisms. Further downstream a beaver pond bordered by Hibiscus, roses, dogbane, spotted jewelweed, and beds of brilliant green knotweed is still the color of tea, naturally dyed by decaying vegetation. Northeast Creek turned brown with the recent storms, hopefully not only because of the massive grading at sites just north of RTP. The poor water quality tolerant carp are jumping in the Creek, and they are the subject of my article in the latest issue of Chatham County Line (

The elms are flowering

This is an article I wrote for the February issue of the Parkwood Inside/Out. We are planning trash cleanups on March 28th and a hike, and will be participating in the costume parade downtown on March 21st and other events for Durham Creek Week 2015. Check this website for announcements and all events will also be posted at:

Creek Week Events

Parkwood’s elms are blooming

Red maples dotting the still bare landscape with blots of crimson are one of the first signs that spring is here, but elms are among the first trees to flower. These prominent trees might be less appreciated because an elm in flower is stormy grey or lime green. Winged elms are the most common species, especially in central Parkwood, but there are slippery elms along the streams and probably American elms, and there are scattered Eurasian ornamentals. The most prominent and beautiful elm I know of in the area is the classically fountain-shaped tree on Highway 54, across from . Because its limbs are all high above the ground, it is hard to identify the species.

Elms, especially American elms, are beloved for the fountain or vaselike shape of mature trees, and there is a graceful symmetry to elms generally. Their leaves and branches alternate, creating an airy lattice effect. The straight veins in their oval leaves, double toothed like a pruning saw, are straight and parallel, but elms also have a very unsymmetric feature – the leaf bases are lopsided, especially in American and slippery elms. Elms have thin, elegant branches, strengthened by very tough wood, and the bark of some species can be twisted into rope. They produce wind pollinated bisexual flowers in early spring, developing into small seeds with a circular flange that drift with the wind several weeks later. The elms generally like moist soil, but winged elms seem to grow in drier soil as well.

The massive, spreading elm in front of Carrboro’s Town Hall could be an American elm (it is big enough for a plaque, yet nothing identifies the species), and I think there are labelled American elms in the Coker Arboretum at UNC. American or white elms are around, but are less common after the arrival of Dutch Elm Disease, a fungus that came to the US around 1930, and is spread by introduced and native beetles that bore in elms. Many elms have been killed, especially American elms, but this seems to be a little less catastrophic than the introduction of chestnut blight and emerald ash borer beetles, and the disease can be managed. American elms are large trees with furrowed bark, brownish leaf buds, and their leaves and stems aren’t very hairy, or less so than slippery elms. Their seeds have some hairiness, while the seeds of slippery elms lack hairs. Both American and slippery elms have large, sandpaperlike leaves, but American elms have greenish flowers, unlike slippery elms. Because their wood is so strong and resistant to splitting, and grips screws tightly, American elms have been used to make things like sports equipment, boats, flooring, crates, and kitchen cutting blocks. Many were planted for landscaping in the northeast, though they grow throughout the eastern USA. In A Natural History of Trees, botanist and nature writer Donald Culross Peattie wrote “If you want to be recalled for something that you do, you will be well advised to do it under an [American] Elm – a great Elm, for such a tree outlives the generations of men; the burning issues of today are the ashes of tomorrow, but a noble Elm is a verity that does not change with time. And although Elms too are mortal, great ones are remembered as long after they are gone as are great men.”

Slippery elms are similar to American elms, but smaller and less vaselike. They have been called red elms, having hairy, reddish leaf buds and reddish flowers, as well as hairy twigs. Their inner bark is slippery and becomes mucouslike when chewed. This inner bark was used to make tea and flour and was used for a variety of internal and external problems and still has an FDA approved medical use. American elm bark was used medicinally by Native American groups.

Winged elms are named for the cork flanges that line their twigs to varying degrees. Sweetgums usually aren’t as winged as elms and their leaves are very different. Winged elms leaves are smaller, smoother, and more symmetrical than those of other elms, and large trees have light brown bark. I think these are the first elms to flower, with brownish flowers that turn into silvery, hairy seeds. As with most trees, winged elms grow a lot when they first leaf out in spring, delicately etched leaves surging forth from the twig tips at a fast clip. The tiny, silky looking new leaves hang as if limp, but are actually strangely stiff. Snow, ice, and maybe hurricanes smashed many of the spindly young loblollies behind the Fire Station around 2002, leaving winged elms, ash, and a few surviving pines as the dominant tall trees, to be replaced themselves by oaks, hickories, and beech in coming decades.

Many animals chew on elm branches, leaves, and seeds, including opossums, rabbits, and bobwhites. The caterpillars that fed on elms are like a who’s who of moths and butterflies, including many of the moths you might see at your porchlights this spring. Double-toothed prominent moth caterpillars feed only on elms. They bite into a leaf and then rest there, so their jagged backs appear like the missing leaf edge. It is surprising that this camouflage works, since elm leaves are emerald green, but the caterpillars are pale seafoam blue and green.