Nomenclature and Classification
When Linnaeus took up Magnolia in his Species plantarum (1753), he created a genus of only one species: Magnolia virginiana. Under that species he described five varieties (glauca, fœtida, grisea, tripetala and acuminata). In the tenth edition of Systema naturae (1759), he merged grisea with glauca, and raised the four remaining varieties to species status.
By the end of the 18th century, botanists and plant hunters exploring Asia began to name and describe the Magnolia species from China and Japan. The first Asiatic species to be described by western botanists were Magnolia denudata and Magnolia liliiflora, and Magnolia coco and Magnolia figo. Soon after that, in 1794, Carl Peter Thunberg collected and described Magnolia obovata from Japan and at roughly the same time Magnolia kobus was also first collected.
With the number of species increasing, the genus was divided into the two subgenera Magnolia and Yulania. Magnolia contains the American evergreen species Magnolia grandiflora, which is of horticultural importance, especially in the United States, and Magnolia virginiana, the type species. Yulania contains several deciduous Asiatic species, such as Magnolia denudata and Magnolia kobus, which have become horticulturally important in their own right and as parents in hybrids. Classified in Yulania, is also the American deciduous Magnolia acuminata (Cucumber tree), which has recently attained greater status as the parent which is responsible for the yellow flower colour in many new hybrids.
Relations in the family Magnoliaceae have been puzzling taxonomists for a long time. Because the family is quite old and has survived many geological events (such as ice ages, mountain formation and continental drift), its distribution has become scattered. Some species or groups of species have been isolated for a long time, while others could stay in close contact. To create divisions in the family (or even within the genus Magnolia), solely based upon morphological characters, has proven to be a nearly impossible task.
By the end of the 20th century, DNA sequencing had become available as a method of large scale research on phylogenetic relationships. Several studies, including studies on many species in the family Magnoliaceae, were carried out to investigate relationships. What these studies all revealed was that genus Michelia and Magnolia subgenus Yulania were far more closely allied to each other than either one of them was to Magnolia subgenus Magnolia. These phylogenetic studies were supported by morphological data.
As nomenclature is supposed to reflect relationships, the situation with the species names in Michelia and Magnolia subgenus Yulania was undesirable. Taxonomically there are three choices; 1: to join Michelia and Yulania species in a common genus, not being Magnolia (for which the name Michelia has priority); 2: to raise subgenus Yulania to generic rank, leaving Michelia names and subgenus Magnolia names untouched; or 3: to join Michelia with genus Magnolia into genus Magnolia s.l. (a big genus). Magnolia subgenus Magnolia can not be renamed because it contains Magnolia virginiana, the type species of the genus and of the family. Not many Michelia species have so far become horticulturally or economically important, apart for their wood. Both subgenus Magnolia and subgenus Yulania include species of major horticultural importance, and a change of name would be very undesirable for many people, especially in the horticultural branch. In Europe, Magnolia even is more or less a synonym for Yulania, since most of the cultivated species on this continent have Magnolia (Yulania) denudata as one of their parents. Most taxonomists who acknowledge close relations between Yulania and Michelia therefore support the third option and join Michelia with Magnolia.
The same goes, mutatis mutandis, for the (former) genera Talauma and Dugandiodendron, which are then placed in subgenus Magnolia, and genus Manglietia, which could be joined with subgenus Magnolia or may even earn the status of an extra subgenus. Elmerrillia seems to be closely related to Michelia and Yulania, in which case it will most likely be treated in the same way as Michelia is now. The precise nomenclatural status of small or monospecific genera like Kmeria, Parakmeria, Pachylarnax, Manglietiastrum, Aromadendron, Woonyoungia, Alcimandra, Paramichelia and Tsoongiodendron remains uncertain. Taxonomists who merge Michelia into Magnolia tend to merge these small genera into Magnolia s.l. as well. Botanists do not yet agree on whether to recognize a big Magnolia genus or the different small genera. For example, Flora of China offers two choices: a large Magnolia which includes about 300 species, everything in the Magnoliaceae except Liriodendron (tulip tree), or 16 different genera, some of them recently split out or re-recognized, each of which contains up to 50 species. The western co-author favors the big Magnolia genus, whereas the Chinese co-authors recognize the different small genera.
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