| Materials toward a monograph of the genus Verbena. XVIII H N Moldenke (1964) Phytologia 10: 89-161 | |
| Materials toward a monograph of the genus Verbena. XXIX H N Moldenke (1965) Phytologia 11: 435-507 | |
| Additional notes on the genus Verbena. XXIV H N Moldenke (1977) Phytologia 36: 117-158 |