It is not native to Japan. Its ultimate origin is tropical America (Central/South America), but it spread widely in the Old World long before Columbus because its seeds were valued as a strong laxative (purgative). In China it was known as *kenniu* (牽牛), with the seeds called *kenniuzi* / *kengoshi* (牽牛子). Japanese envoys to Tang China (or possibly via other routes such as Baekje) brought the seeds primarily for medicinal use.
### Key historical points
- **Early use**: Cultivated mainly for the seeds (as a medicine), not the flowers. It was initially called *kengo* or *kengoshi*, not “asagao.” The name “asagao” (morning face/glory) became associated with it later (by the Heian period or around the 10th century in some records). Note that “asagao” in earlier literature such as the *Man’yōshū* often referred to other plants (e.g., bellflower or rose of Sharon).
- **Early evidence**: Blue, wild-type flowers appear in the national treasure *Heike Nōkyō* (1164) at Itsukushima Shrine. White and other simple color variants appeared over the following centuries, but variety remained limited for nearly a millennium.
- **Shift to ornamentals**: Appreciated for its flowers by the Heian period, but it became a major horticultural plant only in the Edo period (1603–1868). Major “asagao booms” occurred in the Bunka–Bunsei (c. 1804–1830) and Kaei–Ansei (c. 1848–1860) eras, when Japanese breeders developed hundreds of mutant “henka-asagao” (variant morning glories) with unusual flower shapes, colors, and leaf forms—something unique to Japan.
In short: introduced in the 8th century (Nara period) from China as a medicinal herb; turned into a celebrated ornamental (and genetic research plant) centuries later through Japanese cultivation.
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