The tree that got sick, and the one they went to find
Between the late 1980s and the mid-1990s, two fungus diseases wrecked the dogwoods that Tennessee nurseries grew. Researchers went looking for a tree the diseases had not ruined — and found one growing in Maryland.
This whole note is about one kind of dogwood: the flowering dogwood, Cornus florida, the one that grows wild in eastern North America. (USDA’s sales line does not split by species — it counts the dogwoods a nursery sells as flowering trees — so the quiz says “dogwood trees”; the sources here are about this species.) Start with the thing almost everyone gets wrong, Biscuit included. The wide white “petals” on its branches are not petals, and the whole showy thing is not one flower. North Carolina State University’s Extension Gardener Plant Toolbox says it in a single sentence: “The showy dogwood ‘flower’ is actually a cluster of small, true flowers surrounded by four petal-like bracts.” A bract is a leaf that has changed its job: instead of catching sunlight it advertises, the way a petal does. The University of Tennessee’s UT Gardens describes the same four white parts as “not petals at all. They are actually scales that become showy bracts.” And the toolbox adds a detail you can check yourself in spring: “Showy bracts emerge before the leaves.” So if you want the real flowers, look at the little greenish knot in the middle of all that white. The knot is the bouquet. The white is the poster.
Basis: North Carolina State University Extension Gardener Plant Toolbox, “Cornus florida (Flowering Dogwood),” Description and Quick ID Hints; University of Tennessee, UT Gardens, “March 2017 Plant of the Month: Flowering Dogwood.” Quotations unchanged.
Now the trouble. The University of Tennessee Research Foundation tells it plainly: “In the late 1980s to mid-1990s, two fungal diseases wreaked havoc on dogwood trees in Tennessee. Dogwood anthracnose and powdery mildew were infecting and decimating the number of dogwoods raised and sold by nurseries. The resulting costs to control these diseases were crippling the nursery industry in Tennessee and forcing smaller nurseries out of business.” A fungus is neither an animal nor a plant, and some kinds live on other living things and take what they need from them. What the growers needed was not a stronger spray. It was a tree the diseases did not ruin — and it was researchers at the University of Tennessee Institute of Agriculture, not the nurseries, who went to find one. The foundation says: “They started looking for specimens with previously demonstrated resilience to one or both diseases. They located one such species in Maryland, brought a specimen back to Tennessee, and cloned it.” Cloned, here, means grown from pieces of that one tree, so that every new tree is a copy of the one they found still standing. The copy got a name — Appalachian Spring — and the foundation says it “is still the single cultivar scientifically proven to be highly tolerant to dogwood anthracnose and resistant to powdery mildew.” Read that carefully: tolerant is not the same as immune. The Maryland tree gave one cultivar, not a whole family — the foundation says the same researchers “also developed five other flowering dogwood cultivars, each with different characteristics, that were resistant to powdery mildew,” and UT Gardens calls the group “The Appalachian series of dogwood introduced by researchers with the University of Tennessee Institute of Agriculture.” One healthy tree found in Maryland; one cultivar from it; and a series of other work beside it.
Basis: University of Tennessee Research Foundation, “UTRF Startup Develops Disease-Resistant Dogwoods for the Nursery Industry” (March 23, 2018); University of Tennessee, UT Gardens, “March 2017 Plant of the Month: Flowering Dogwood.” Quotations unchanged.
A flowering dogwood is not a forest giant and never tried to be. The toolbox calls it “a woody, deciduous, showy, understory tree” that is “native from southeastern Canada through eastern North America to eastern Mexico,” and says it is “usually growing under larger forest trees and at woodland edges.” Understory means the layer beneath the big trees — the room under the roof. It grows “15 to 25 feet tall,” about as high as a two-storey house. Deciduous means it drops its leaves each autumn. Its red fruits, the toolbox notes, “are a food source for songbirds and other wildlife from fall through winter.” None of which explains the strange thing about this tree: a small, modest, shade-loving plant that four different states decided to make a symbol of themselves.
Basis: North Carolina State University Extension Gardener Plant Toolbox, “Cornus florida (Flowering Dogwood),” Description. Quotations unchanged.
The two university pages this note leans on do not fully agree about that tree, and it is worth saying so out loud. The research foundation calls Appalachian Spring “highly tolerant to dogwood anthracnose and resistant to powdery mildew.” The North Carolina plant toolbox, in its list of dogwood varieties, describes the same one as “white flowers, resistant to dogwood anthracnose, susceptible to powdery mildew.” One is a university extension’s plant database, written for gardeners; the other is the university research foundation’s own account of the work. Both are trying to be useful. They still say different things about the mildew — and neither of them says immune about anything. When two good sources disagree, the honest move is not to pick the more exciting one. It is to show you both and say which part is still open.
Basis: University of Tennessee Research Foundation, “UTRF Startup Develops Disease-Resistant Dogwoods for the Nursery Industry” (March 23, 2018); North Carolina State University Extension Gardener Plant Toolbox, “Cornus florida (Flowering Dogwood),” Cultivars / Varieties. Quotations unchanged.
Dogwood wood is famously hard. The plant toolbox lists what people made from it: the wood is “hard, heavy, close grained and strong” and was “often used for textile shuttles and spools as well as handles for tools.” A shuttle is the piece that shoots back and forth across a loom, thousands of times a day, carrying the thread — a job that chews through soft wood. The same page says the plant “was used for medicinal purposes by Native Americans, as well as for carvings, looms, and disinfectant.” So the tree people now buy for two weeks of spring was, for a long time, a tree people wanted for the part you cannot see.
Who says so: North Carolina State University Extension Gardener Plant Toolbox (opens in a new tab)
Stories travel with this tree, and the people who know it best say so out loud. UT Gardens, writing about the flowering dogwood, notes “much history and folklore behind Cornus florida from the Native Americans’ belief of ‘little dogwood people’ who served as protectors and guardians, to legend of its use in the crucifixion.” The page calls those things history and folklore, and then draws a line: “However, there are some things we know to be fact.” The facts it goes on to give are that the dogwood is native to Tennessee, and that the four white parts are not petals. That is a good habit to copy — tell the story, then say which part you can check.
Who says so: UT Gardens, University of Tennessee Institute of Agriculture (opens in a new tab)
So why do Tennessee growers take in more dogwood money than growers anywhere else? (Money is what USDA can rank here; the column that counts the trees themselves hides too much to rank.) None of the sources used here says, so what follows is possibilities, not findings. One is that the help arrived where the trouble was: the research foundation says the disease-resistant cultivars came out of a Tennessee university, and that “for each new cultivar that is released by CAT, Tennessee nurseries receive a three-year exclusive right to produce and sell that cultivar,” which the foundation describes as “a competitive advantage in the market.” But the same page says those cultivars are licensed to growers in North Carolina, Oregon and Japan as well, and it never says the head start explains any state’s ranking. A second possibility runs the other way round: the diseases may have hurt Tennessee so badly precisely because so many dogwoods were already being grown there — which would make the growing the cause and the rescue the consequence. A column of dollars cannot tell you which story is right, or whether it is a third one nobody here has thought of.
※ A hypothesis is an idea that isn't proven yet.
Note: a “theory”, “folklore” or “outlook” is not settled fact. Always check who is saying it.
📊 Sources for the rankings mentioned in this note (links to the original data and retrieval dates) are on each quiz page below.