Taxodium Update by David Creech
Taxodium at SFA Gardens – A 2022 Update
SFA Gardens remains a valued resource at Stephen F. Austin State University (SFA). This 128-acre garden in the Pineywoods of East Texas got its start in 1985 and includes a wide range of rarely encountered woody and herbaceous species. This is a collector’s garden, and one of our most intense collections is Taxodium.
The precise nomenclature for Taxodium remains a matter of some debate. Still considered by many as three species (T. distichum, T. ascendens, and T. mucronatum), we believe there’s enough consensus in recent literature to list Taxodium distichum as a single species with three botanical varieties (Arnold et.al. 2007 and Adams et.al. 2012).
Taxodium distichum (L.) Rich.var. distichum (Baldcypress - BC)
Taxodium distichum var. imbricarium (Nutt.) Croom (Pondcypress - PC)
Taxodium distichum var. mexicanum (Carriere Gordon) (Montezuma cypress - MC)
Our history with Taxodium includes connecting with the Taxodium Breeding and Improvement Program at the Nanjing Botanical Garden in the late 1990s (Creech et.al. 2011). I have been making the trek to China once or twice a year since 1997. Of course, that is until Covid descended on our life in March of 2020. In the last twenty plus years I have become close friends with the leader of that program, Professor Yin Yunlong, and his hard-working staff. They have visited SFA many times and we’ve enjoyed graduate students and exchange scientists from his program, as well as Nanjing Forestry University. I consider them the world’s primary research team on this fascinating and ancient genus. In China, Yin Yunlong has observed that MC hybrids show super-parent advantage in height, trunk diameter, biomass increase and no knees. That last trait is very important. One of the great negatives associated with bald cypress is the development of knees (pneumatophores). BC typically produces knees. MC and the hybrids with MC do not. With great potential in timber, energy, carbon sinks, and water conservation forests, MC hybrids are widely used for urban and rural greening, shelterbelts for farmland, and forests for coastal areas in southeastern China. The scale of Taxodium use in China needs to be seen to be appreciated but it is in the millions of trees planted and that continues to this day. The “greening” of China is real and our native bald cypress is part of that mix.
Chinese scientists believe that controlled Taxodium hybridization can combine the best characteristics of superior parents and allow for selection of superior clones. My friend Yin Yunlong once said, “everyone agrees that superior parents produce superior children.” Selection criteria in the Nanjing Botanical Garden for controlled cross and open pollinated seed crops includes growth rate, salinity and alkalinity tolerance, flooding tolerance, needle blight resistance, form/shape, fall color and ease of cutting propagation. In this paper, the term “hybrids” refers to the progeny of crosses between botanical varieties of Taxodium distichum. In several studies in China and here at SFA, the hybrids demonstrated improvements in growth rate, salt and alkalinity tolerance, form and vigor. We have provided trees for some very high pH test sites in central Texas and have a large collection of hybrids planted in our plots at Moody Gardens on Galveston Island in a high salt environment. They get an A for salt and alkalinity tolerance.
The breeding program in China can be summarized as controlled cross and open pollinated seedlings grown out in large fields at close spacing (about 6” to 1’ apart in rows 4’ apart is typical).
After the first year, they are then cut off near the ground. That last step results in upright shoots and the strongest leader is favored. They usually grow 4-5 feet in the second year and selections are made then. The selections are propagated by cuttings, rooted, planted out and then allowed to grow to provide a foundation for cutting generation. Four to six-inch cuttings in June with an overnight hormone dip is a typical strategy in China. Young seedlings provide wood that typically root quite well. Cutting wood from old trees root poorly or not at all. One strategy is to cut the trees back severely all the way to the trunk which generates plenty of vigorous growth. Thick, robust green cuttings root better than thin twiggy wood. From my experience, the key to success depends more on the actual age of the clone and the nature of the cutting wood than hormones. Because they are cutting grown, the resultant plants typically exhibit plagiotropic growth (growing more or less divergent from the vertical, also referred to as topophysis. That is they tend to be “branch-like” and don’t form a leader unless pruned and trained. Upright growing shoots, however, begat upright growing trees.
Out of a about a dozen advanced selections from China, one BC X MC clone has emerged that is superior simply because it is quite free of needle blight, Cercosporidium sequoia. It was tested as T406 and with Nanjing Botanical Garden’s permission, we named it ‘LaNana” after the creek that traverses this university (Creech 2017). In our region of Texas and all the way across the Gulf South, Montezuma cypress can be affected by needle blight (McDonald et.al. 2008). ‘LaNana’ has proven to be highly resistant in our cooperator plots while other selections can be quite dramatically impacted, some years worse than others. For instance, we have another clone (T502, named ‘Banita’) which is almost evergreen in most winters, keeping old needles until the new growth emerges in March, the degree of needle drop depending on the severity of hard freezes. The term for foliage retention long into the winter is marcescent. ‘Banita’ is very fast growing and features light green foliage but lacks resistance to needle blight in some of our test locations in the humid Gulf South. However, in central Texas and parts west, it appears free of the malady.
One final question has been answered. After winter storm Uri in mid-February 2021, we can report that all of our Taxodium collection came through without any damage. With an all-time record low of -3oF in Nacogdoches, we now have a benchmark for hardiness. Since none of the hybrids have ever experienced such a low temperature, this was a great test and we now have the promise of a more northern range limit. The December 1983 and 1989 freezes and the February 2021 freeze provided hard evidence that even straight MC is surprisingly hardy.
If you are interested in trialing the hybrid bald cypress, we suggest you make a trip to the Pineywoods of Texas. We’ll give you a fine windshield tour of the collection and if we have them on hand in small sizes, we do love to share. Let’s keep planting.
LITERATURE CITED
Robert Adams, Mike Arnold, Andrew King, Geoffrey Denny, David Creech. 2012. Taxodium (Cupressaceae): One, Two or Three Species? Evidence from DNA Sequences and Terpenoids. Phytologia 94 (2): 159 – 168. http://www.phytologia.org/uploads/2/3/4/2/23422706/94(2)159-168adamsetal_taxoduim_dna.pdf
Arnold, M. and G. Denny. 2007. Taxonomy and Nomenclature of Baldcypress, Pondcypress, and Montezuma Cypress: One, Two, or Three Species? HortTechnology 17 (1): 125-127.
David Creech, Lijing Zhou, Yin Yunlong, and Teobaldo Eguiluz-Piedra. 2011. Can Taxodium be Improved? Arnoldia 69/2: 11-20. http://arnoldia.arboretum.harvard.edu/pdf/articles/2011-69-2-can-taxodium-be-improved.pdf
David Creech. 2017. Taxodium X ‘LaNana’ – Born in America and Mexico, Improved in China. https://dcreechsite.com/2017/01/03/taxodium-x-lanana-born-in-america-and-mexico-improved-in-china/
Garry Vernon McDonald, Geoffrey C. Denny, Michael A. Arnold, Donita L. Bryan, and Larry Barnes. 2008. Comparative Canopy Damage among Provenances of Baldcypress Associated with the Presence of Cercosporidium sequoiae (Ellis and Everth.) W.A. Baker and Partridge. HortScience Volume 43 (6): 1703–1705. https://journals.ashs.org/hortsci/view/journals/hortsci/43/6/article-p1703.xml