Back in 2010 as I was poring over the freshly-published New Trees tome, I came across the bizarre profile of an unfamiliar tree. In this groundbreaking work, which is now available entirely online at treesandshrubs.com, I was introduced to an absolute wealth of taxa that were new to me. For some reason, I have always been drawn to species that fly under the radar; whether it is due to rarity or a lack of horticultural merit, something about little-known and seemingly ignored taxa appeals to me. Perhaps it’s the challenge of integrating them into a landscape or educational exhibit to successfully display them and create a conversation, despite the overall lack of excitement they tend to generate. In this category, I place some very interesting ecological stories such as the hemiparasitic Buckleya and Pyrularia species, as well as Dalbergia hupeana, a true rosewood without much to recommend it aside from being a cold-hardy outlier in a generally tropical genus.
My initial impression of Dipentodon and its single species, Dipentodon sinicus, led me to group it with these other little-known species of questionable horticultural merit. Sounding more like a name for a large extinct reptile, the name Dipentodon sounds fairly unusual for a plant name. The name means “twice five teeth” in reference to an unusual morphology in which the flowers appear to have a ten-lobed perianth. Scientific names relating to teeth are much more common in the animal kingdom, and as a child that loved dinosaurs, it was not uncommon to see names that end in -don within that group.
The search for Dipentodon began as a quest to obtain a plant that was almost unknown in horticulture and seemingly unobtainable. In addition, it held that special appeal to me that only a botanical curiosity with few other traits to recommend it can inspire. Something about woody plants that are far outside of my realm of experiences inspire a sense of curiosity and urge for discovery that is difficult to describe. And indeed, Dipentodon was far outside of those experiences. Belonging to a small clade of families that are obscure even to many botanists, Dipentodon contains a single species with few relatives… and none that are commonly cultivated. Its family, Dipentodontaceae, is also thought to include a second genus that can be found throughout Central America, Perrotetia; however, the placement of the latter has been problematic and, as the Angiosperm Phylogeny Group notes, it has been frequently misidentified.
I started my attempts by noting the locations they mention of cultivated specimens; this was a short list, with only the San Francisco Botanical Garden and Tregrehan Garden in Cornwall, U.K. noted as growing the species. I started with the former; if they were willing to share, it would be much easier to exchange plant material with an institution in the United States. Importation of plant material from outside of the country requires permitting, which is a potentially long and odious task. Unfortunately, SFBG no longer had Dipentodon in their collection, but recommended that I reach out to Tom Hudson at Tregrehan. As it happens, Tom was able to assist and offered to share seed; unfortunately it was a bit too late in the season and the Dipentodon capsules had already burst and flung their seeds throughout the garden. This was an interesting tidbit that I have not seen mentioned in the literature! Witch-hazels (Hamamelis) includingour native species, have a similar dispersal mechanism.
Fortunately, I remembered to contact Tom the following year. I also had the good fortune of an easy permitting process; since Dipentodon is so little known and has no close relatives that are known to harbor any ecological or pathogenic risks, the approval process through APHIS to import some seeds from Cornwall was simple and straightforward. Limeledge will be one of only a scant few institutions assessing this species in all of North America and making the species accessible to the public. Since Dipentodon is so poorly known and almost completely untested, I have no idea how it will perform in CNY, or if it will even survive. However, in science, even a series of failures will provide us with data! Performance in Washington state at Far Reaches indicates that the species can have spectacular red fall color and has had no issues with cold hardiness. If it is as adaptable as early assessments seem to indicate and demonstrates little risk of becoming a pest, Dipentodon sinicus could be a landscape tree of the future.