Acacia longifolia -- California

Yes, the species has naturalized in South Africa, Australia (Western Australia), New Zealand, Europe (France), the southwestern US, and South America (Brazil, Argentina, Uruguay). [USDA GRIN]

The following areas where the species has naturalized are similar to the climate of the focal area (California, USA):
USA (California), South Africa, Southern Europe (Spain, Portugal, southern France, Italy), Western Australia (disjunct from native range). (GBIF)

The following areas where the species has naturalized are dissimilar in climate:
New Zealand (North Island),
South America (east coast of Argentina, Uruguay, Colombia)

The species has "become invasive in other parts of Australia (Victoria, New South Wales), in New Zealand, South Africa, Spain, Portugal and Brazil." (Global Invasive Species Database)
Several published scientific papers list the species as invasive. (Marchant et al. 2008, Rodríguez-Echeverría et al. 2009)

The species has "become invasive in other parts of Australia (Victoria, New South Wales), in New Zealand, South Africa, Spain, Portugal and Brazil." Areas in Australia (New South Wales), South Africa, Spain and Portugal are similar in climate to the focal area. (Global Invasive Species Database)
Several published scientific papers list the species as invasive in the Mediterranean in areas that are similar in climate. (Marchant et al. 2008, Rodríguez-Echeverría et al. 2009)

Acacia paradoxica is on the California noxious weed list (CDFA)
3 other Acacias are on the California Invasive Plant Council Inventory as of this writing (January 2020) (Cal-IPC, 2020)

The following areas where the species occurs are similar to the climate of the focal area (California, USA) and make up more than 50% of the range:
USA (California), South Africa, Southern Europe (Spain, Portugal, southern France, Italy), most of the Southeastern Australia (native range), central Australia, Western Australia (disjunct from native range), a small area in central Japan. (GBIF)

The following areas where the species has naturalized are dissimilar in climate:
New Zealand (North Island), South America (east coast of Argentina, Uruguay, Colombia),

Noted as one of the most aggressive invasive species in dunes in Portugal, causing significant ecological impacts (Marchante et al. 2008). The species was also noted changing the native species composition in Portugal, shading out native species (Marchante et al. 2003).

Noted as being invasive and "often associated to fire events" in Portugal (Marchante et al. 2008). The seeds are stimulated by fire (Marchante et al. 2003).
"In terms of changes in fire regimes, the presence of A. longifolia (especially thickets) increases the risk and intensity of fires." (Global Invasive Species Database)

Toxicity listed as none [USDA Plants Conservation Plant Characteristics].
No significant information found on the FDA poisonous plants database.
Not listed in the Canadian Poisonous Plants Information System - Canadian Biodiversity Information Facility (CBIF).

Plants grow fairly wide (San Marcos Growers).
The species is noted to form thickets, growing wide on many stems (Global Invasive Species Database).

No mention of reproducing vegetatively despite a lot of information about formation of thickets. All sources indicate reproduction by seed.

No information found to indicate this. The species could fragment, but it is not documented as a common reproductive method.

Indicated that the species may be propagated by seed [USDA Plants Conservation Plant Characteristics]
Kew indicates that 50 year old seed is 12% viable [Kew Seed Information Database]

Fruit/seed listed as copious (USDA Plants Conservation Plant Characteristics)
"Acacia longifolia produces large quantities of seeds annually (up to 11,500 per tree), which are thought to be viable for 50 years. In Portugal often more than 90% of the seeds are viable (E. Marchante, pers. comm.)." (Global Invasive Species Database).
"Acacia longifolia plants in long‐invaded and recently invaded areas produced similar amounts of seeds (average under the canopy, 12000 seeds · m–2) each season..." (Marchante et al. 2010)

Some informal information indicating very high germination in the field in Portugal. (GISD)
Some research indicating high viability (95%), but some dormancy. This research also indicates that the species is fire sensitive as opposed to requiring fire (Auld & O'Connell 1991).

The trees reach sexual maturity at 2-3 years. (Global Invasive Species Database)

Calflora lists flowering for 3 months in the summer. [Calflora]

Published study of the species in Portugal indicates that the seed has a hard seed coat, ants may disperse the seeds only short distances and that most seeds fall within a short distance of the parent plant.

No adaptation for this type of dispersal listed. In fact, published literature indicates the formation of a very dense, localized and persistent seed bank by the hard-coated seeds.

No evidence of special mechanism for dispersal this way. Not commonly a contaminant.