The Disappearance of Harbison Hawthorn (Crataegus harbisonii Beadle)
Hawthorns have been, well, a thorn in the side of taxonomists for some time. In Eastern North America, this group is very diverse. The reproductive biology of hawthorns allows for rampant hybridization, as well as the perpetuation of distinctive individuals through a process called apomixis, in which very little (if any) genetic reassortment occurs. As a result, it has been challenging to thoroughly delineate species boundaries and establish effective species concepts in the field; this led to a situation in which hundreds of species have been described in North America alone. Many of these names have been reduced to synonyms, while others have not been seen since their description and constitute little more than footnotes in botanical history.
In some cases, hawthorns that appear to have been locally abundant in the past have become either extremely rare or have disappeared entirely. This is the case for the Harbison hawthorn (Crataegus harbisonii Beadle), which is a member of Section Coccineae, Series Triflorae, a small group of obscure Southeastern species. Harbison hawthorn appears to have been first collected in the Nashville area in 1877 before being described by Chauncey Beadle as a new species in 1899. When Beadle formally published the description for this species, he noted that there were numerous specimens at the type locality from which it was described. Another noted hawthorn expert, C.S. Sargent, noted that it was common in that area through the first half of the 20th century. However, the species failed to turn up in surveys after 1948.
The apparent rapid decline of this species led modern-day hawthorn experts Ron Lance and J.B. Phipps to mount surveys to find the missing hawthorn beginning in 1993, which led to the discovery of only two remaining individuals in the wild. The story of the initial rediscovery is recounted in Ron Lance’s incredible book on hawthorns in the Southeastern U.S. Shockingly, the team found one of the two remaining individuals almost immediately, and did not find another until the following year. By 1998, repeated searches yielded no additional trees, and it appeared that the species had been reduced to only two individuals in the wild… one of which died shortly after being discovered. Fortunately, more were to be found later. In 2019, ecologist Barry Hart discovered a second and much larger population in nearby Obion County, although “much larger” in this case means 30 plants instead of just two. While this is still a dangerously small number, it grants additional hope for the survival of the species.
Despite being so rare, the species flowers and fruits well quite well in cultivation, and the seeds exhibit a high germination rate. The seedlings themselves develop into vigorous, strong-growing individuals with relatively large dark green leathery leaves, large flowers, and fairly large fruits compared to other hawthorns. Talent and Dickinson (2005) investigated the chromosome count of various hawthorn and medlar species, finding that C. harbisonii was a tetraploid. The uniformity of seedlings in cultivation has led researchers to consider that this species reproduces apomictically; in other words, very little sexual reproduction and reassortment of genes occurs, resulting in a population of plants with very similar, if not identical, traits. This uniformity could be a contributing factor to the rapid decline of the species in its historical range; with limited genetic diversity, the species would struggle to cope with rapid changes to its environment such as those related to development, changes to the local wildfire regime, and the arrival of invasive species.
As a group that causes a lot of confusion for amateurs and specialists alike, and is also abundant in Central New York, hawthorns are of special interest to us at Limeledge. Some species such as C. harbisonii are extremely rare or have interesting ecological or even historical importance, which make them excellent subjects for educational programming. Limeledge Botanical Garden and Arboretum has one accession of Harbison hawthorn, from Woodlanders Nursery. Their source appears to be from fruiting specimens at the North Carolina Arboretum where Ron Lance was able to propagate the single remaining wild tree from the Davidson County site. Therefore, our tree appears to be a seedling derived directly from that original sole survivor.
At Limeledge, one of the most common hawthorns on the property keys out to Holmes hawthorn, (C. holmesiana Ashe). This species is also in Section Coccineae, but unlike Harbison hawthorn, it is related to a more northern group of species including the widespread scarlet hawthorn (C. coccinea L.). Indeed, it is sometimes considered merely a synonym for that species. Although Holmes hawthorn toils in almost complete obscurity, it occurs across a wide range and does not appear to be threatened. However, it seems to be nowhere common… with an exception being that it is locally abundant in some limestone areas in Central New York. Palmer (1925) notes that its type locality (where the specimens came from that allowed it to be described to science) is “central New York”, an interesting bit of botanical lore that is also an encouraging sign that it is not in danger of facing the same fate as the Harbison hawthorn.
Are you aware of any other tree species that were described from Central New York? Reach out to arboretum@limeledge.org!
