Encyclopedia : Taxonomy

Plants and classification of genus Ipomoea

Academic names of the morning glory, Ipomoea nil and its related species

Copyright 1998-2012 Yoshiaki Yoneda
A meeting on the "Status and future of the study of the morning glory" was held at the suggestion of Professor Shigeru Iida of the National Institute for Basic Biology. The meeting took place in the Okazaki conference center in December 1999. At that meeting the present author gave a lecture on "the morning glory and its closely related species". This lecture's principal concern was the academic names of the morning glory and related species, and changes in those names. What the author wishes to confirm remains substantially undiscussed, but the author will mention the abstract.

Though one variety of Convolvulus hederaceus in the first edition (1753) of Linnaeus's Species Plantarum was assumed to correspond to Ipomoea nil, in the second edition (1763), the academic name of Convolvulus nil L. to Ipomoea nil was first recorded, as was that of Convolvulus purpureus L. to Ipomoea purpurea. Linnaeus mentioned Ipomoea nil's habitat was North America. As the Convolvulus of Linnaeus was recognized to have considerably heterogeneous species by later taxonomic studies, the genus Calystegia was newly proposed and some species included in Convolvulus were moved to Ipomoea or to the new Calystegia. Roth moved Convolvulus nil L. and Convolvulus purpureus L. into genus Ipomoea in 1797. Thus the name of the morning glory became Ipomoea nil (L.) Roth.

The morning glory, Ipomoea nil, was assumed to have been introduced to Japan from China, probably in the Nara era, judging by old descriptions found in herbal documents. Then when would the morning glory in Japan and China have been introduced to Europe? Could it have been already introduced there before the morning glory received its academic name in the 18th century? The European who observed Japanese plants precisely and drew their figures is Kaempfer, who stayed in Japan for two years from 1690. By his illustrations, representative plants of Japan were introduced to Europe. The fifth volume of Amoenitatum Exoticarum (Kaikoku-kikan), described after Kaempfer's return to Europe, includes Catalogus Plantarum Japonicarum (Nihon-shokubutu-si) (1712), in which he made simple mention of a lot of Japanese plants. Kaempfer described one of the items he observed as "Kingo, vulgo Asagawo", in the flower grass class. Although he had no illustrations of the plant, this item described the morning glory clearly, indicating that documentation of the morning glory had reached Europe by the beginning of the 18th century. It is said that Kaempfer investigated Japanese plants by referring to Kinmou-sui (1666), a catalog by Tekisai Nakamura. In the herb flower class of this book, we find the following explanation: "Kengo is a flower of Asagao. The name of its seed is Kengoshi. The name of its vine is Kuji-sou". Accompanying this description is an illustration of the morning glory climbing up and twisting around a fence. Kaempfer probably observed the morning glory by referring to this figure.

Linnaeus adopted a figure of the morning glory of Dillenius as a standard specimen of Convolvulus nil L. in the second edition of Species Plantarum (1763). We do not know the relation of Dillenius or Linnaues with Nihon-shokubutu-si written by Kaempfer.

Subsequently Thunberg, a pupil of Linnaeus, visited Japan in 1775~1776. In his Flora Japonica (1784), he described vulgo asagawo or the Japanese morning glory in detail, giving it the name of Ipomoea triloba. Willdenow (1799) enlarged Linnaeus's Species Plantarum, and cited the Ipomoea triloba of Thunberg under the heading of Convolvulus nil L. This seems to be the first reference to the Japanese morning glory with the academic name of Convolvulus nil L. in the literature. The Latin name chosen by Thunberg was changed to Ipomoea triloba L. by Keisuke Ito in his Taisei-shokubutu-meiso (1829).

Then A. Franchet and L. Savatier (1875), studying Japanese plants, called the Japanese morning glory Pharbitis triloba Miq. The same name, Pharbitis triloba, was assigned also by Yoshio Tanaka and Motoyosi Ono in Yuuyou-shokubutu-zusetu (1891). In the Meiji era, when Western learning entered Japan and botany was brought about, the academic name of the morning glory seems not to have been settled yet in Japan. As indicated above, the Japanese morning glory had several Latin names in Japan at first. Soon, however, Pharbitis nil (L.) Choisy was adopted in general.

In 1833, Choisy proposed the new genus Pharbitis, which has three carpels, and separated it from Ipomoea (four or two carpels). Under this system, the morning glory was designated Pharbitis nil (L.) Choisy. When this proposed use of Choisy entered into Japan, Tomitarou Makino first assigned the name Pharbitis nil Chois. to the Japanese morning glory in Zoutei Soumoku-zusetsu (1907-1913), as originally described by Yokusai Iinuma. The name Pharbitis nil Choisy was used in a lot of illustrated books edited by Michio Murakoshi. Since then, this academic name has been used broadly in Japan as well as in the floricultural world in general. Since his first edition (1925) of the Illustrated Flora of Japan, Makino used Pharbitis nil Chois. for the Japanese morning glory, except for Ipomoea nil Roth, which appeared in his 1940 edition.

However, the genus Pharbitis of Choisy was not supported internationally. After the Index Kewensis (1895), compiled by British taxonomists integrated all members of the Pharbitis genus into the Ipomoea genus, the international community stopped referring to the Pharbitis genus. There has been a history of intense international argument to establish a uniform plant nomenclature rule. A committee for such a rule has been meeting regularly, and its results have been summarized as the International Code of Botanical Nomenclature. In this Code, Pharbitis is now preserved as a conserved generic name. For example, in Nihon no yaseishokubutsu (Wild flowers of Japan) (1981), an illustrated book of Japanese flora, the morning glory is classified in the genus Ipomoea.

On the other hand, the common morning glory, bred horticulturally in Europe and America, has been called Ipomoea purpurea (L.) Roth for a long time. In addition, the dawn flower is also considered to belong to genus Ipomoea.

Considering that the characteristic of three carpellar pistils was not enough to justify proposing an independent genus, the author adopted Ipomoea nil (L.) Roth as the academic name of the morning glory here and Pharbitis nil Choisy as a synonym for it. After considering the history and gardening points of view in Japan, for this morning glory database the author decided to describe Pharbitis nil, Asagao, the morning glory, as Ipomoea nil (Pharbitis nil). The results of recent molecular phylogenetic studies of Eiji Nitasaka support the classification of the morning glory in a section of genus Ipomoea.

Academic names and synonyms of representative plants in section Pharbitis are as follows. Please refer to the image and detailed morphological explanation.

Asagao Ipomoea nil (L.) Roth, of ancient introduction to Japan.
Synonym Convolvulus nil L., Spec. Pl., ed. 2 (1762) p.219 (in part)
____Pharbitis nil Choisy in Mem. Soc. Phys. Geneve VI (1833) p.439;
____in DC. Prodr. 9 (1845) p.342

Amerikaasagao Ipomoea hederacea Jacq. Collect. 1 (1786) p.124 naturalized in Japan
Synonym Convolvulus hederaceus L. Sp. Pl. (1753) p.154
____Pharbitis hederacea Choisy in Mem. Soc. Phys. Geneve VI (1833) p.440;
____in DC. Prodr. 9 (1845) p.344

Marubaasagao Ipomoea purpurea (L.) Roth, Bot. Abh. (1787) p.27 Roth,
____bred in Europe and North America
Synonym Convolvulus purpureus L., Spec. Pl., ed.2 (1762) p.219
____Ipomoea hispida Zucc., Cent. Obs. (1806) n.36
____Pharbitis hispida (Zucc.) Choisy in Mem. Soc. Phys. Geneve IV (1833)p.438
____Pharbitis purpurea (L.) Voigt, Hort. Suburb. Calc. (1845) p.354

Noasagao Ipomoea indica (Burm.) Merrill, Interpr. Rumph. Herb. Amb. (1917) p.445,
____native to Japan
Synonym Convolvulus indica Burm., Index Univers.Herb.Amb. VII (1755) p.6
____Ipomoea congesta R.Br., Prodr. Fl. Nov. Holl. ed. 1 (1810) p.485
____Convolvulus acuminatus Vahl, Symb. Bot. III (1794) p.26
____Ipomoea acuminata (Vahl) Roem. & Schult., Syst. IV (1819) p.228
____Convolvulus congesta (R.Br.) Spreng., Syst. I (1825) p.601
____Pharbitis insularis Choisy in Mem. Soc. Phys. Geneve VI (1833) p.439
____Pharbitis acuminata (Vahl) Choisy in DC., Prodr. IX (1845) p.342
____Pharbitis congesta (R.Br.) Hara, Enum. Sperm. Jap.1 (1948) p.166

Images of the genus Ipomoea


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Edited by Yuuji Tsukii (Lab. Biology, Science Research Center, Hosei University)