A Global Rarity
Acer pentaphyllum, or the five-leaf maple, is a large shrub or small tree endemic to southwestern Sichuan Province in China, where it has an extremely limited distribution consisting of four populations along the steep gorges of the Yalong River. The Red List of Acer: revised and extended, published in 2020, reports Acer pentaphyllum as Critically Endangered, noting that it may be restricted to as few as 500 trees in the wild. Significant human and non-human threats exist to its wild populations.
First collected by Joseph Rock in 1929, and later described and named in 1931 by Professor Diels of the German State Botanic Garden at Berlin-Dahlem, plants of Acer pentaphyllum were notoriously rare in cultivation through the 1900s. Only three established specimens at San Francisco Botanical Garden (then Strybing Arboretum) were known, with all other plants in horticulture thought to be descended from them. However, a precious gift of wild collected seed was received in 1992 by William McNamara of Sonoma Botanical Garden (then Quarryhill Botanical Garden), sent to him by Dr. Yin Kaipu of the Chengdu Institute of Biology, and resulting in new wild provenance specimens in cultivation. Further collections were made by various partners and collaborators in 2001, 2005, and 2010, resulting in the establishment of a few hundred specimens of known wild provenance in ex situ collections.
Vulnerability Of Ex Situ Collections
While numerous wild origin specimens now exist ex situ, there are still significant threats to these cultivated plants and given the perilous state of the wild populations, these collections are of critical importance. Of principle concern is that the vast majority of the living specimens are held between just two institutions – Sonoma Botanical Garden and UBC Botanical Garden. Having such a repository of a Critically Endangered species concentrated on two sites puts ex situ security in a similar situation as the remaining wild plants – human or natural disaster could quickly destroy a significant portion of known living specimens. Indeed, those at Sonoma have been seriously threatened by recent fires that have impacted the garden. Increased threats from natural disasters linked to climate change put the safety of these ex situ holdings in uncertain territory considering long-term safeguarding.
A Strategy for Success
Recognizing the vulnerability of the ex situ collections, a new project has been developed in by the University of British Columbia Botanical Garden as a partnership between the Global Conservation Consortium for Acer and The Plant Collections Network Acer Multisite Group of The American Public Gardens Association. The goal of the project is to establish a collaborative network actively involved in the conservation of Acer pentaphyllum to ensure a healthy, secure, and accessible metacollection of Acer pentaphyllum ex situ, and eventually support actions for in situ conservation work.
In 2021 work commenced at UBC Botanical Garden where a 5-year strategy was developed to guide the project, and the first phase of vegetative propagation tests were initiated. Rootstocks are currently being grown to support grafting of ex situ collections, and garden origin seedlings of Acer pentaphyllum have been produced to support the refinement of propagation protocols without impacting vulnerable wild collected specimens. The garden origin seedlings will also be useful in horticultural trails to better understand how to cultivate and care for Acer pentaphyllum in garden settings.
Once propagation protocols are established a prioritized approach to backing up wild collected accession will commence, allowing each specimens to be duplicated in their garden of origin as well as distributed across a network of gardens. Through this process, we can safeguard important ex situ collections of Acer pentaphyllum, providing some level of security for this threatened plant against stochastic events in an increasingly unpredictable future.
By Ben Stormes.
BGCI (2021). PlantSearch online database. Botanic Gardens Conservation International. Available at www.bgci.org. Accessed on 15/02/2021.
Crowley, D., Barstow, M., Rivers, M. and Harvey-Brown, Y. (2020). The Red List of Acer, Revised and Extended. Botanic Gardens Conservation International.
McNamara, W.A. (2002). Making a last stand: Acer pentaphyllum. Paciﬁc Horticulture:
Plant Collections Network (2021). Acer Multisite Group Inventory (unpublished). The American Public Gardens Association.
Royal Botanical Gardens, Kew (2021). Plants of The World Online. http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:56774-1. Accessed on 22/08/2021