Hibiscus cannabinus L., native to Africa and India, has been cultivated as a fiber crop for many centuries. Recently, we found it has been naturalized to central, southern and eastern low altitudes in Taiwan. This alien species is very similar to H. sabdariffa L. but is distinguished from the latter by the corolla yellow with crimson center, and the lobe of calyx long caudate and white tomentose, each lobe with a gland at the base and epicalyx spiny. A taxonomic treatment, distributions, habitats, color photographs, line drawings, and voucher specimen were provided to aid identification.