Pacific Cooperative Studies Unit, University of Hawaii at Manoa, Department of Botany
Abstract
Reports were scanned in black and white at a resolution of 600 dots per inch and were converted to text using Adobe Paper Capture Plug-in.Verbascum thapsus, common mullein, is a biennial weed of roadsides, pastures, and open and semi-open natural habitats. This report reviews the autecology of V. thapsus in its native range (Eurasia) as well as in Hawai'i and elsewhere where it has naturalized. V. thapsus exhibits many characteristics of an ideal weed; broad germination conditions, self-compatibility, high seed output and a long-lived seed bank. Populations can vary substantially in life history characters, which may have allowed the species to spread over such a wide geographical range, including most temperate parts of the world. V. thapsus was introduced to the island of Hawai'i about 100 years ago, and it still appears to be spreading. It has invaded sites from sea level to the summit of Mauna Kea, but the densest populations occur in upper montane and subalpine habitats. Outside of Hawai'i, it is a poor competitor in many habitats, relying on continuous disturbance to maintain its populations. In contrast, in Hawai'i common mullein appears to have spread in little-disturbed native habitats, particularly where vegetation is sparse such as on relatively recent lava flows. Little is known about the impact this may have on the native biota. Further studies are needed to determine if the spread of V. thapsus depends on disturbance in Hawai'i. Extreme stem and inflorescence fasciation in V. thapsus appears to be unique to Hawai'i; its cause and how it affects life history characteristics are not known. While certain herbicides are effective in killing common mullein, long-term control is very difficult due to its abundant, long-lived seeds. No biocontrol agents have been introduced to Hawai'i, although a number of insects and pathogens attack it and its seeds elsewhere
