Bald cypress knees (Taxodium distichum ‘Pendens’ 806-52*A).
Bald cypress knees (Taxodium distichum ‘Pendens’ 806-52*A). Photo by Kyle Port Kyle Port

If the needles are dropping off of your cut Christmas tree–most likely a fir (Abies) or pine (Pinus)–you know it’s time for it to go to the compost pile. Likewise, if a fir, pine, or other evergreen conifer (spruce [Picea], juniper [Juniperus], yew [Taxus], arborvitae [Thuja], etc.) growing in your yard dropped all of its foliage it would be a sure sign that something was drastically wrong with the plant. Conifers are supposed to keep their leaves all year, right?

Well, not necessarily. While it’s true that the majority of conifers are evergreen (they retain foliage for a full year or more), the word “conifer” is not synonymous with “evergreen.” There is a small group of conifers that grow and drop a new set of leaves every year, just like maples, birches, or other deciduous trees. There are five genera of these deciduous conifers, four of which grow in the Arboretum.

The larches (Larix) are the largest group of deciduous conifers with 11 species widely distributed in northern regions of North America and Eurasia. Tamarack, aka eastern or American larch (L. laricina), is one of three North American species; it has a wide range in northern tier states from Maine to Minnesota as well as much of Canada and Alaska. Taxodium is another North American genera of deciduous conifers, the most common species being bald cypress (T. distichum), noted for its iconic buttressed trunk and knees [PDF].

Dawn redwood, Metasequoia glyptostroboides, in the fall.
Dawn redwood, Metasequoia glyptostroboides, in the fall.

The other three deciduous conifer genera are all native to China (and Vietnam in one case), and, curiously, all are monotypic, meaning there is only one species within each genus. Golden larch (Pseudolarix amabilis) is a particularly handsome tree, its common name coming from the vibrant golden yellow its needles turn in autumn before dropping. The grove of golden larch (accessions 3656, 16779, 10764, and 187-94*A) along Bussey Brook at the southwest end of the Conifer Collection is a must-see at the Arboretum. And then there’s  dawn redwood (Metasequoia glyptostroboides), a signature tree at the Arboretum (it’s featured on our logo and there’s a magnificent specimen 524-48*AA across from the Visitor Center). Read the whole story of the Arboretum’s involvement in the discovery and distribution of dawn redwood here [PDF].

The remaining deciduous conifer is not hardy at the Arboretum. Water pine, or Chinese swamp cypress (Glyptostrobus pensilis), is native to limited areas in southeast China and Vietnam; it is hardy only to USDA Zone 8 (average annual minimum temperature 10 to 20 degrees F [-6.7 t0-12.2 degrees C]).

For a thorough overview of the gymnosperms–the plant group that includes conifers, ginkgos, and the fascinating Welwitschia, among others–see this Arnoldia article [PDF].

From “free” to “friend”…

Established in 1911 as the Bulletin of Popular Information, Arnoldia has long been a definitive forum for conversations about temperate woody plants and their landscapes. In 2022, we rolled out a new vision for the magazine as a vigorous forum for tales of plant exploration, behind-the-scenes glimpses of botanical research, and deep dives into the history of gardens, landscapes, and science. The new Arnoldia includes poetry, visual art, and literary essays, following the human imagination wherever it entangles with trees.

It takes resources to gather and nurture these new voices, and we depend on the support of our member-subscribers to make it possible. But membership means more: by becoming a member of the Arnold Arboretum, you help to keep our collection vibrant and our research and educational mission active. Through the pages of Arnoldia, you can take part in the life of this free-to-all landscape whether you live next door or an ocean away.

For more tree-entangled art, science, and writing, subscribe to Arnoldia by becoming a member of the Arnold Arboretum.