Ailanthus Altissima - Taxonomy

Taxonomy

The first scientific descriptions of the tree of heaven were made shortly after it was introduced to Europe by the French Jesuit Pierre Nicholas d'Incarville. D'Incarville had sent seeds from Peking via Siberia to his botanist friend Bernard de Jussieu in the 1740s. The seeds sent by d'Incarville were thought to be from the economically important and similar looking Chinese varnish tree (Toxicodendron vernicifluum), which he had observed in the lower Yangtze region, rather than the tree of heaven. D'Incarville attached a note indicating this, which caused much taxonomic confusion over the next few decades. In 1751, Jussieu planted a few seeds in France and sent others on to Philip Miller, the superintendent at the Chelsea Physic Garden, and to Philip C. Webb, the owner of an exotic plant garden in Busbridge, England.

Confusion in naming began when the tree was described by all three men with three different names. In Paris, Linnaeus gave the plant the name Rhus succedanea, while it was known commonly as grand vernis du Japon. In London the specimens were named by Miller as Toxicodendron altissima and in Busbridge it was dubbed in the old classification system as Rhus Sinese foliis alatis. There are extant records from the 1750s of disputes over the proper name between Philip Miller and John Ellis, curator of Webb's garden in Busbridge. Rather than the issue being resolved, more names soon appeared for the plant: Jakob Friedrich Ehrhart observed a specimen in Utrecht in 1782 and named it Rhus cacodendron.

Light was shed on the taxonomic status of ailanthus in 1788 when René Louiche Desfontaines observed the samaras of the Paris specimens, which were still labelled Rhus succedanea, and came to the conclusion that the plant was not a sumac. He published an article with an illustrated description and gave it the name Ailanthus glandulosa, placing it in the same genus as the tropical species then known as A. integrifolia (white siris, now A. triphysa). The name is derived from the Ambonese word ailanto, meaning "heaven-tree" or "tree reaching for the sky". The specific glandulosa, referring to the glands on the leaves, persisted until as late as 1957, but it was ultimately made invalid as a later homonym at the species level. The current species name comes from Walter T. Swingle who was employed by the United States Department of Plant Industry. He decided to transfer Miller's older specific name into the genus of Desfontaines, resulting in the accepted name Ailanthus altissima. Altissima is Latin for "tallest", and refers to the sizes the tree can reach. The plant is sometimes incorrectly cited with the specific epithet in the masculine (glandulosus or altissimus), which is incorrect since botanical, like Classical Latin, treats most tree names as feminine.

There are three varieties of A. altissima:

• A. altissima var. altissima, which is the type variety and is native to mainland China.
• A. altissima var. tanakai, which is endemic to northern Taiwan highlands. It differs from the type in having yellowish bark, odd-pinnate leaves that are also shorter on average at 45 to 60 cm (18 to 24 in) long with only 13–25 scythe-like leaflets. It is listed as endangered in the IUCN Red List of threatened species due to loss of habitat for building and industrial plantations.
• A. altissima var. sutchuenensis, which differs in having red branchlets.