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Horticultural Reviews, Volume 49


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species.

      Hydrangea section Cornidia is located almost exclusively in Mexico, Central America, and along the western coast of South America (McClintock 1957). The only exception within this section is H. integrifolia Sieb. which is found in Taiwan and the Philippines. This section contains at least 12 known species, including the relatively recently discovered H. albostellata (Samain et al. 2014) in Mexico. Species in this section are root‐climbing lianas that occur in the primary rainforest and are unique by being functionally dioecious and having evergreen leaves. Interestingly, many of the species which occur in the tropical regions of South America are confined to the high altitudes of the Andes Mountains where the climate is more temperate (McClintock 1957). Several of these species are at risk of extinction due to habitat loss (Samain et al. 2014) and further exploration is required to determine if more previously undescribed taxa exist.

      In Asia, Hydrangea are distributed from the Himalayan Mountains in the west to Japan in the east and south to the Indonesian islands. Some of the Asian taxa are confined to the islands on the eastern edge of the continent (i.e., H. sikokiana Maxim., H. hirta Sieb., and H. involucrata Sieb. are mostly found in Japan). However, most of the Asian hydrangeas are also distributed across the continental mainland (McClintock 1957).

      Several Hydrangea fossils have been discovered, including in Alaska (Hollick 1925), Idaho (Niklas and Brown 1981), and Oregon (Manchester 1994). Although the evidence is limited to sepal fossils for the Idaho and Alaska specimens, a more complete inflorescence represents the specimen from Oregon. Based on the available evidence it seems as though the specimens may represent extinct species and suggests that the prehistoric range of hydrangea in North America was much larger.

      Oakleaf hydrangea was first encountered by William Bartram during his 1773–1777 exploration mission throughout the southeastern United States. He published the first description of the species in his monograph describing his travels (Bartram 1791). The first specimen he described was located along the “brook called Sweet Water” (which is possibly now known as Sweetwater Creek, west of Macon, GA) in south‐central Georgia (Bartram 1791). The species was introduced to Europe in 1803 but details of the export remain elusive (Lawson‐Hall and Rothera 1995).

Schematic illustration of a map of historic </p>
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