Source: https://www.cal-ipc.org/plants/paf/volutaria-tubuliflora-plant-assessment-form/
Timestamp: 2019-04-20 05:14:27+00:00

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When V. tubuliflora was first detected in San Diego it was mis-identified as V. canariensis, and is still listed in the Jepson eFlora as V. canariensis. Recenly, Chris McDonald determined that a specimen from Orange County in Newport Bay from 1987 was also V. tubuliflora, moving the introduction date and location to 1987 in Orange County.
The clone of Volutaria that has established at least at the Anza Borrego and Newport colonies are both a naturally uncommon floral morph. This is apparently the same morph that has invaded Chile. However, this morph is uncommon in the native V. tubuliflora range of northern Africa/Mediterranean basin. If all three widely separated California infestations are determined to be the same genotype and also the same as that is in Chile, then it is likely (not certain) that all of the California infestations originated from a single introduction, and dispersed thereafter (Vanderhoff, pers. comm.). I agree the most likely path of Volutaria spread in California is a single introduction and then more local spread out from the first infestation (McDonald, pers. comm.).
Deep taproot may draw down the water table, but no studies have been done to document this. Primarily occurs in dry habitats with deeper water table, does occur adjacent to desert washes where moisture is likely to be higher than surrounding areas (McDonald, pers. comm.).
It is possible that stands of V. tubuliflora could become dense enough to crowd out native vegetation. "My best estimate is that it can outcompete native plants. In Newport there are very few other weeds when the Volutaria canopy is thick (McDonald pers. comm.)." The population in Chula Vista is dense and appears to have been growing for several years (Giessow, pers. comm.).
Based upon field observations, this is a very early germinator (Sept. In Newport Beach), but with only one year of experience as a basis. This very early germination is much sooner that the native flora and likely shades and inhibits the native species. This is similar in phenology to adjacent invasive species in these same areas, such as Brassica nigra, Sisymbrium irio and Bromus spp. There is even observed competition among these species. My other comment has to do with possible allelopathic qualities. Phytotoxins and phenols appear to be documented in several species of the closely related Centaurea genus, although a quick search did not reveal any studies of this with Volutaria. (Vanderhoff, R. pers. comm.).
V. tubuliflora becomes tall enough to block movement of animals, if it grows in dense stands. This is occurring in Orange and coastal San Diego County populations. Herbivores seem to prefer native annuals to Volutaria. In the field Volutaria is generally not well grazed by herbivores (most likely caterpillars) and usually only shows minor damage (McDonald, C. pers. comm).
Volutaria and its close relative Centaurea are not represented by any native species in California so there is no opportunity to cross with native species and cause impacts to genetic integrity.
The pathway for establishment of V. tubuliflora in California is unknown. However, where it has been introduced it spreads rapidly in areas prone to seasonal flooding or along roadsides. It is highly likely that if it is introduced elsewhere it will quickly establish, with or without disturbance. In early 2017 a new large population was found in Upper Newport Bay, located about a mile from the infestation discovered in March 2015. The population contained thousands of plants in some very dense patches, indicating it is not recently established (Vanderhoff, pers. comm.). The two Newport colonies are in rather highly traveled areas and the occurrences tend toward road and trail edges first, but do extend into nondisturbed areas (McDonald, Burger and Vanderhoff, pers. comms.).
In desert it occurs in disturbed and undisturbed areas equally (McDonald, pers. comm). This question is scored as Severe since V. tubuliflora can establish in undisturbed areas.
V. tubuliflora was first thought to be introduced in Borrego Springs in 2010, with a small number of plants observed in 2011, 2012 and 2013. After the monsoonal flooding in summer 2013, almost one thousand plants germinated in the mud left behind by the water. After Borrego Springs finally got some decent winter rain in late 2014, almost ten thousand plants germinated, a factor of ten more plants than were seen one year earlier. In early 2017 a new large population was found in Upper Newport Bay, located about a mile from the infestation discovered in March 2015. The population contained thousands of plants in some very dense patches, indicating it is not recently established (Vanderhoff, pers. comm.). Recently an herbarium specimen from 1987 from the population in Newport Bay was determined to be V. tubuliflora, moving the introduction date back to that time. This indicates the rate of spread of the Newport Bay population is perhaps B, increasing less rapidly (Vanderhoff, pers. comm.), however Burger considers the rate of spread as an A for the Newport Bay population. This question is scored as A since the Borrego Springs population is thought to be increasing at that rate.
V. tubuliflora was first discovered in Borrego Springs in 2010, with a small number of plants observed in 2011, 2012 and 2013. After the monsoonal flooding in summer 2013, almost one thousand plants germinated in the mud left behind by the water. After Borrego Springs finally got some decent winter rain in late 2014, almost ten thousand plants germinated, a factor of ten more plants than were seen one year earlier. V. tubuliflora was detected in Orange County in 2015 with as many as 3,000 plants, and recently R. vanderhoff located another population with thousands of plants a mile from the previous detection (Vanderhoff pers comm.). In 2016, Jason Giessow reported a 1.2 acre population with over 50,000 plants in Chula Vista, coastal San Diego county. This population is likely a few years old given its density and extent (Giessow 2016).
It is not known how V. tubuliflora was introduced into California, but human introduction is the likely vector. Since its introduction it has been found along roadsides, in disturbed areas and at trail heads. Its also found in 3 well separated populations each about 80 miles apart. So long distance, and most likely human, dispersal seems quite probable (McDonald, C. pers. comm.).
V. tubuliflora was observed to be spreading after flooding-induced rains in Borrego Springs. It could also be spread by wind.
Dispersal distances can be over 1 km (McDonald, pers. comm.).
V. tubuliflora is native to the Canary Islands, northern Africa and southern Europe. It is also invasive in Saudi Arabia and Chile. In Chile it grows in arid desert in an area with 20 to 30mm annual precipitation (Tellier 2014). While it has invaded desert habitats in San Diego County, its presence in Newport Bay and coastal San Diego County indicate it has the potential to spread into more community types which are not yet invaded.
V. tubuliflora occurs in desert dunes and scrub, as well as coastal scrub and urban road edges in Southern California. Currently populations are small where it occurs (Calflora).

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