Distylium 2.0
Distylium Little Boxer
Michael A. Dirr

Distylium 2.0

Features - Mike’s Plant World

See how this crop went from anonymity to celebrity with breeding breakthroughs.

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Swing Low features dark blue-green leaves and is one of the lowest growing selections.

In the “Manual of Woody Landscape Plants” 1998 edition, Distylium racemosum was afforded a paragraph. I knew little and the text reflected that fact. The 2009 edition broadened the presentation of D. racemosum and added D. myricoides. I observed the species and several cultivars (‘Guppy’- small leaves; ‘Akebono’- cream new leaves, maturing green; and Mr. Ishii’s Variegated – splotched white and green) at the JC Raulston Arboretum (Raleigh, North Carolina), The Biltmore Estate (Asheville, North Carolina), the Sir Harold Hillier Gardens and Arboretum (Hampshire, England), and the Coastal Georgia Botanical Gardens (Savannah, Georgia). None offered commercial potential except for the dedicated collector.

I am unable to articulate what possessed me to adopt Distylium as a plant orphan. I added a D. racemosum in 1996 to the woody trials at the UGA Horticulture Farm but it never impressed. Still there and less impressive. What was the impetus to start this journey that opened the floodgates to new, unique, landscape adaptable, broadleaf evergreen cultivars for Zones 7 to 9? The story unfolds below.

The evolution

Distylium traveled from obscurity to landscape prominence since the first patented cultivar introductions from the University of Georgia and Plant Introductions Inc., with Blue Cascade (‘PIIDIST-II’ PP24,409) and Emerald Heights (‘PIIDIST-I’ PP24,410) in McCorkle Nursery’s Gardener’s Confidence brand. McCorkle passed on ‘Vintage Jade’ (PP23,128, issued October 23, 2012), the first patented Distylium, which landed in First Editions. Coppertone (‘PIIDIST-III’ PP25,304), Linebacker (‘PIIDIST-IV’ PP25,984), Cinnamon Girl (PIIDIST-V’ PP27,631), and Swing Low (‘PIIDIST-VI’ PP29,779) were bred by Plant Introductions Inc., and introduced by Bailey Nurseries via First Editions.

Jewel Box (‘BLDY01’ PP32,816), Cast in Bronze (‘BLDY02’ PP32,758), and Magic Globe (‘BLDY03’ PPAF) are 2021-22 patents from Buddy Lee and introduced through the Southern Living Plant Collection. Robert Head patented Bluescape in 2019 (‘RLH-DM1ER’ PP30,514), a Distylium myricoides selection, marketed in the Garden Debut brand. Spring Frost (‘sPg-3-007’ PP25,833) was patented in 2015 by the Southern Plant Group.

My son, Matt, has five selections from his work at UGA under trial at McCorkle and Greenleaf Nurseries and three were submitted for patent protection. His Little Boxer (‘DISmd-26-18’ PPAF) possesses small, lustrous dark green leaves and mounded-spreading compact habit akin to Ilex crenata ‘Convexa’. Little Boxer will be introduced through Van Belle Nursery’s Bloomin’ Easy brand in a cooperative arrangement with Greenleaf Nursery.

The Distylium cultivar cupboard is much richer than in 2012 when ‘Vintage Jade’ was patented/released. Breeding continues at the new PII, Premier Introductions Inc., and I suspect other operations. In 2020, PII selected a beautiful variegated leaf seedling with pink, rose, and white emerging foliage, transitioning to bronze-purple, then dark green. Foliage is species size and the habit restrained, 2-3 feet by 3-4 feet. From numerous seedlings of Emerald Heights, this was the only selection of merit. In 2021, Blue Cascade, Emerald Heights, Cinnamon Girl, and Tall-3 (upright form) yielded all manner of variation with more variegated seedlings than I experienced through the years. Several upright pyramidal and columnar types are being evaluated, one emulating ‘Sky Pencil’ holly in outline.

A fair question to ask is how did the UGA Distylium journey start? Piroche Plants (now Seklon and Sons Nursery) in Pitt Meadows, British Columbia, was started by Pierre Piroche in 1987, who imported plants from China. The offerings were rich, and I purchased for trial those that might prove useful for the Georgia nursery industry. Distylium purchases included D. racemosum, D. myricoides and D. myricoides ‘Emerald Elf’ (‘Lucky Charm’). My technician, Vickie Waters, and I noticed one seedling that appeared to be a hybrid (later determined to be so). This and each of the above were planted at the Horticulture Farm circa 2002/03 for testing. It’s safe to state that none of these four as they existed would excite the industry or gardeners. In fact, they grew so large and unkempt that the two D. myricoides and suspected hybrid were cut to the ground several times.

Vickie collected/cleaned/sowed seed from the suspected hybrid on 9-27-2005 and the initial 21 seedlings (germinated 12-19-2005) were planted in 2006/07 at the Horticulture Farm. From these, Blue Cascade, Emerald heights, and ‘Vintage Jade’ were selected. The variation in the seedlings indicated hybrid origin and Donglin Zhang (UGA) showed via molecular markers they were hybrids. All introductions from UGA and PII are hybrids and any bred from these carry the D. myricoides and D. racemosum genes. D. myricoides was severely injured during the 2014-15 winter (5°F) while D. racemosum was not affected. The hybrids showed gradations of damage, from 100% brown leaves to no damage (Emerald Heights). My hardiness zone range estimate for the hybrids is 7-9, with Cinnamon Girl as the hardiest selection.

In the Dirr garden many of PII’s throw-away seedlings were liberally planted in sun and shade locations. None have faltered and, in fact, several grew so large that I chain-sawed them to bare gray stems. All regenerated and continue to be pruned for size control. Although full sun is preferable, moderate shade allows for a quality plant. I have several plants in oak shade and they are presentable. Our garden is 13 years old with Distylium present from the beginning. No insects, diseases, or environmental stresses have occurred. Tender spring new shoots are susceptible to late winter/spring frosts. For residential and commercial landscapes, they are as close to foolproof as a biological entity can be. I remember J. Guy of Carolina Nurseries walking the Horticulture Farm planting and saying, ‘Who would buy a plant with the common name of Isu tree?’ He was partially correct, for no one uses the common name, as Distylium dominates the conversation.

Jewel Box (left) and Cast in Bronze at Griffith Nursery.

Production

Seed and cutting propagation have presented no major hurdles. The small two-valved capsules need to be collected in early fall when turning brown but before dehiscing. Collect capsules and place in paper bags to dry and seeds are expelled in a few days. Fresh seed germinates without pretreatment; however, two to three months of cold-moist stratification is recommended for old/dry seed. Often, root radicals emerge from seeds in the stratification medium. Firm cuttings can be rooted year-round using 1,500 to 4,000 ppm KIBA. Cinnamon Girl is one of the more difficult to root cultivars and requires the higher concentration.

In production, the root systems are always at the bottom of the container, where water is concentrated. I have yet to plant one in a permanently wet location but believe it would survive.

Cultivars

The newer cultivars (less Blue Cascade, Emerald Heights and ‘Vintage Jade’) are presented below based on my breeding and growing experiences. There will be more introductions as the nursery and landscape industries created demand for a genus that was mired in obscurity.

Vintage Jade forms a spreading mound in the landscape. These are 7 years old.

PII bred and Bailey introduced cultivars

Cinnamon Girl - Personal favorite with plum-purple new growth, maturing dark blue-green. Small leaves and compact, spreading-arching growth habit create refined, graceful appearance. No foliar cold damage at 5°F during 2014-15 winter in Athens. My observations indicate it is the most cold-hardy of the PII/Bailey introductions. Grows 2-3 feet high, 3-4 feet wide. I used large masses of Cinnamon Girl fronted by Loropetalum ‘Crimson Fire’ in entrance plantings in our subdivision. Five years later, the Loropetalum is taller than the Distylium, which is 2½ feet high.

Coppertone - Unique copper-orange-tinged emerging foliage, transitioning to blue-green. Habit is stiffer than Cinnamon Girl and a bit irregular with age. The lone plant in our garden was injured during the 2014-15 winter. Reaches 3-4 feet high and 4-5 feet wide. Best in Zone 7b.

Linebacker - In 2008-09, PII was breeding for smaller sizes and many seedlings grew excessively tall and were composted. Several with pretty hued new growth were field-planted as an afterthought. Bailey decided to run with Linebacker because of potential for screening and hedging and the red new growth; mature leaves lustrous dark green. The original 6-foot high, 3- to 4-foot-wide plant was shaped like a whiskey barrel. I noticed a tendency to become more shrub-like in container production. In our garden, the plants never resembled the original and were removed. Listed in promo material as 8-10 feet high, 6-8 feet wide.

Swing Low - The last of the Bailey introductions from PII breeding work. PII field-planted a row of the best low growing selections in 2013, all derived from Blue Cascade. This selection with dark blue-green leaves was one of the lowest growing, and plants in containers exhibit a similar habit. It was marketed as 2-3 feet by 4-6 feet, but I have yet to observe a plant of that size.

Comparing habits of Vintage Jade (front) and Emerald Heights at UGA.

PDSI/Southern Living Plant Collection

Buddy Lee and I often discuss breeding at the IPPS-SR meetings. Buddy is always open and insightful about his activities. He was working on Distylium either before me or at the same time. Based on the patent descriptions for Jewel Box, the process started with open-pollinated seedlings in 2009 and selection in 2012. The Cast in Bronze timeframe was 2007 seedlings and 2012 selection. The following three selections are listed as hybrids. I have grown the first two in our garden. Yet to access Magic Globe. I believe Jewel Box has much to offer.

Cast in Bronze - Habit is more wild and woolly than Jewel Box with spreading, fine-textured shoots, initially bronze-maroon, maturing shiny dark green. I observed blocks of same-age Jewel Box and Cast in Bronze side by side, with Cast in Bronze twice as large. Listed at 3-4 feet by 3-4 feet and Zone 7a-9b.

Jewel Box - Compact shrub with distichously arranged leaves forming a V-shaped trough, the shoots densely borne and radiating from the center of the plant at 30 to 45° angles. The “look/texture” is decidedly different from the PII/Bailey cultivars. Foliage is described as blue-green, but plants in our garden are rich green at maturity. Grows 2-3 feet high and 3-4 feet wide. Zone 7a-9b.

Magic Globe - Is new to me and I have yet to add it to the garden. Photos show a rounded dark green foliage shrub, the leaves smaller than the species. Grows 3 feet high and wide. Zone 7a-9b.

Emerald Heights survived a 5°F winter at the UGA Horticulture Farm.

Greenleaf Nursery/Garden Debut/Bloomin’ Easy

Bluescape - Was surprised to witness a true D. myricoides cultivar on the market because the species is less hardy than D. racemosum. The Piroche D. myricoides were irregular in habit with wild, splaying shoots. The common name blue Isu tree refers to the dark blue green foliage. The leaves are elliptical in shape compared to the ovate foliage of D. racemosum. This cultivar reaches 1-2 feet high and 3-4 feet wide. I have only observed it in containers and intuitively know it will grow taller than the listed height. Additionally, the foliage was a shiny dark green rather than the blue-green of typical D. myricoides.Distylium myricoides grew 6 feet in height in the UGA trials and over 10 feet high on the Georgia Southern University Armstrong Campus, Savannah.

Little Boxer - I am biased about this selection since my son bred it. The small, exceedingly glossy dark green leaves, elliptic-oblong in shape and thickly set along the stems, produce a boxwood look-alike; hence, the trade name. The habit is rounded-mounded, the stems thin and pliable, creating a fine-textured outline. I estimate 1½-3 feet in height and 3 feet in width. I was showing Dr. Tim Smalley of UGA the plant. Tim was a former student of mine and taught the woody plant courses after I retired. The first word from his lips was, “wow!” Enough said.

Spring Frost - The new growth is cream-yellow, maturing shiny dark green. Plants at Griffith Nursery developed soft yellow foliage. The stems of the emerging shoots are red and rather pretty. Forms a spreading shrub, 2-3 feet high and 3-4 feet wide. Perhaps less cold hardy than others, although listed as Zone 7-9.

The original 4 Distyliums Dirr planted at the Hort Farm circa 2002.

Does the industry need another Distylium introduction? I believe there is an opportunity to breed red and yellow foliage selections. At PII, seedlings with degrees of bronze and red in the new growth are common but eventually become green. Those with mixed mottles of cream, pink, rose, and green persist as the leaves mature. A screening and hedging selection would make a great addition to the current lineup. PII thought Linebacker would be that candidate but is not the perfect solution.

A genus that had no status in nursery and gardening circles has become a commodity plant. Who knew this would happen when the journey started? And may it continue.

For more than 40 years, horticulturist, breeder, and author Michael A. Dirr has impacted the green industry through research, teaching, books, and plant introductions. michirr@aol.com