A linguistic time capsule from 733 CE
In the year 733 CE, a comprehensive report on the Izumo Province was completed and presented to the Japanese imperial court. This document, the Izumo no Kuni Fudoki, is a detailed gazetteer describing the region's geography, myths, and natural resources. It is the most complete of the five Fudoki that survive today from the Nara period (710–794 CE). Within its pages is a list of the area's useful plants, a catalogue that inadvertently preserved an important moment in the evolution of the Japanese language.
The Fudoki lists approximately 127 distinct plant species, each recorded using man'yōgana—Chinese characters used for their phonetic values. This script predates the development of Japan's native syllabic scripts, hiragana and katakana. The plant names provide historical linguists with a snapshot of Old Japanese, the oldest attested form of the language, at a time of phonological change. The way these names were written down captured a sound system that was in the process of simplifying, showing how the language was spoken nearly 1,300 years ago.
The sound of ancient plants
The linguistic feature frozen in the Fudoki's plant list is a phonological system known as Jōdai Tokushu Kanazukai, or "Special Kana Usage of the Ancient Period." In Old Japanese, certain syllables that sound identical today were pronounced differently and written with distinct sets of man'yōgana characters. Linguists distinguish these pairs as Type A (kō) and Type B (otsu). For example, syllables with the vowels 'i', 'e', and 'o' each had two distinct forms.
The Izumo Fudoki is valuable because it was written as this eight-vowel system was collapsing into the five-vowel system of later Japanese. The plant names show this transition in action. Some names are written using characters that reflect the older, distinct vowel sounds, while others show evidence of the merger. For instance, the distinction between the two types of "mo" sounds (/mo₁/ and /mo₂/) is present only in the oldest texts like the Kojiki (712 CE) and had already merged by the time most of the Man'yōshū poetry anthology was compiled around 759 CE. The Fudoki, compiled in 733 CE, sits directly in this transitional period.
This catalogue of flora, intended as a practical survey of resources for the imperial government, became an unintentional record of a language in flux. The names of reeds, trees, and flowers, written down by a provincial official, now provide some of the clearest evidence for how the sounds of an ancient language were changing.