Indigo, one of civilization's oldest dyes, has tinted the robes of Egyptian pharaohs and brightened the clothing of both Chinese peasant and American farmhand (think Levis jeans). Before cotton was "King", indigo was one of the U.S. Deep South's most important cash crops.
Synthetic indigo, formulated in the 1890s by German chemists, signaled the beginning of the end for Taiwan's indigo industry. By the 1920s, local textile mills had switched completely over to synthetic dye stocks.
Recognition: Naturalized hill indigo today grows in northern Taiwan along mountain streams well-shaded by forest canopy. Patches can be found throughout Keelung, eastern and northern Taipei County, and Yangmingshan National Park (and probably other parts of Taiwan too). As hill indigo is not indigenous to the island, significant tracts typically signal areas of previous commercial cultivation. Look for signs of terracing and pits where the dye would have been bleached from leaves.
The herbaceous plant grows to over one meter in height and produces delicate lavender-white flowers during winter (December/January). Its fleshy leaves are serrated and grow to about 11cm in length. Leaves emerge in opposing pairs from the main stem, with leaf pairs alternating at right angles to one another (in a repeating "cross" formation) up the stem.