| Materials toward a monograph of the genus Verbena. VIII H N Moldenke (1963) Phytologia 8: 460-496 | |
| Materials toward a monograph of the genus Verbena. XVIII H N Moldenke (1964) Phytologia 10: 89-161 | |
| Additional notes on the genus Verbena. IV H N Moldenke (1968) Phytologia 15: 478-495 |