Witches’ Brooms – my Epigenetic Epiphany and the Gingko Hermaphrodite

High up in a white pine last summer, on our farm in Salvisa, Kentucky, I spotted something odd. I called my neighbor Otis Knox and asked him if he’d ever seen a Witches’ Broom. He came down to investigate.

Bill Barnes with the wonderful and capable interns of the Morris Arboretum and their completed grafts of Pinus strobus ‘Otis Knox’

I pointed toward the 30” diameter growth. Otis said he had seen Witches’ Broom before, but hadn’t known that’s what they were called. He had not seen this one.

Witches’ Broom is caused by a peculiar, and not fully understood, epigenetic gene expression that goes haywire in trees and occasionally in shrubs. A switch on a gene, ordinarily turned off, is turned on. Or vice versa. The DNA is the same as that of the parent, but an abnormal growth occurs on a portion of the plant due either to a fungus, bacteria, virus, stress hormones or possibly mitochondrial mischief.

Witches’ Broom in white pine

Holly Cooper, my sister-in-law, was the first to notice the white pine Witches’ Broom. I’d walked past it hundreds of times and not noticed a thing.

Holly is not named Holly for nothing. She’s a great gardener and photographer. Her grandfather, Theodore Klein, was a legendary plant collector and Kentucky nurseryman. Mr. Klein had a fondness for hollies, hence Holly’s name. Yew Dell, his home, nursery and garden, in Crestwood, Kentucky, has a beautiful holly allée. Yew Dell Botanical Gardens, since Mr. Klein’s death in 1998, has become a popular public garden.

Otis Knox had brought young white pine, Pinus strobus, seedlings from the mountains of Wolfe County, Kentucky, and planted a sweeping curve of them along our gravel drive in 1976, at what was then his new Salvisa home. The property has changed hands several times since, but Otis didn’t move far away. He lives on a farm across the Salt River from his old home place.

Otis Knox and his white pines

My arborist friend Robert Rollins gathered scion wood from the Witches’ Broom in late January with a long pole pruner. These pieces were sent the next day to two growers to be grafted onto white pine seedling understock.

Robert Rollins holding Witches’ Broom

“Witches’ Broom,” according to Sidney Waxman, in the 1983 Proceedings of the International Plant Propagators Society, “… are dense shrub-like growths that occur as a result of the mutation of buds. They are found mainly on conifers and generally retain their dwarf and dense character when propagated vegetatively.” Witches’ Brooms have been grafted onto seedling understock since 1874, according to Waxman. Over 20,000 seedlings of pines (including white pine), Norway spruce, Larix laricina and Canadian hemlock were grown at the University of Connecticut between 1964 and 1983.

I named the clone in honor of my Salvisa neighbor, but don’t expect to see ‘Otis Knox’ in a glittery rollout, with a brand-marketing program, anytime soon. The beach-ball-sized white pine mutant needs a few more years in Santa’s workshop before it, or its progeny, are unwrapped.

Bill Barnes, and interns from the Morris Arboretum, have grafted a few of these pines. So has Karl Klein, the uncle of Holly Cooper and the son of Theodore Klein of Yew Dell.

Karl Klein with finished graft of ‘Otis Knox’

According to Bill Barnes, a Pennsylvania nurseryman, the grafted Witches’ Broom may not amount to much. The modified plants don’t always behave as they did when they clung to mama. The real action, he says, may come in the next generation. And though white pine Witches’ Broom are a dime a dozen, it will be interesting to watch what happens from the progeny of ‘Otis Knox’.

I could see, from the cut pieces of scion wood, that the remaining Witches’ Broom, hanging in the pine, will be flowering this spring.  Let me do the math…. That certainly means that pinecones could be produced in two years. Seedlings could be underway in three years.  It might take a few more years to see what becomes of the offspring of the Witches’ Broom. They might all die immediately, or they could produce perfectly normal trees. Or there’s the slim chance a few might resemble, well, who knows what?

There’s nothing wrong with normal, of course, but it’s the peculiar outliers that get gardeners’ tongues wagging.

Gingko at Cave Hill Cemetery

There’s a fascinating Witches’ Broom in a huge and spectacular Gingko at Cave Hill Cemetery in Louisville, 63 miles from Salvisa. The male tree was barren and produced no seeds. The tree, planted in the mid 19^th century, suddenly produced a peculiar, stubby growth, high in its branches, late in the 20^th century.

And guess what: The Witches’ Broom was a seed-producing female.

The once male Gingko is now a gender-bending, street-legal hermaphrodite.