Senna artemisioides -- California

Silver senna is native to north western Australia (specifically western New South Wales), but not native to the United States, where it is grown as an ornamental plant. Silver senna is noted as naturalized in the southwestern United States (Wojciechowski et al. 2021). On the Invasive Plant Atlas of the United States, silver senna occurrences have been reported in southern California and southern Arizona, and it is listed as exotic on the website. On the USDA PLANTS database, Senna artemisioides ssp. xcoriaceae is noted as occurring in California.

Silver senna is noted as being naturalized in the southwestern U.S. by the Jepson Manual and other horticultural resources. It is grown as an ornamental shrub. Silver senna occurrences are also noted in South Africa, the Mediterranean Basin, and southeastern Europe (Climate Matching Map for Senna artemisioides).

Jepson notes silver senna as being naturalized in California. There is currently not enough information to assess the invasiveness of Senna in the U.S. or world in a similar climate. The Invasive Plant Atlas of the United States notes that silver senna is not on any state or national invasive species list, but lists the plant as exotic. Calflora lists silver senna as a shrub that is not native to California.
The University of Arizona Desert Legume Program notes Senna artemisioides ssp. petiolaris as having the potential to become invasive, but not to the extent of other Senna artemisioides subspecies in cultivation.
Saguaro National Park lists silver senna (aka feathery cassia) as a non-native shrub that occurs in the park.

There is currently not enough information to assess the invasiveness of Senna in the U.S. or world in a similar climate. The Invasive Plant Atlas of the United States notes that silver senna is exotic, but not on any state or national invasive species list. Calflora lists silver senna as not native to California, and Saguaro National Park lists silver senna as a non-native shrub found in the park, but there is a lack of evidence that lists the plant as invasive. However, there is speculation that silver senna has the potential to become invasive.

Senna spectabilis, an exotic tree of the same genus, is noted as invasive in a similar climate. Senna pendula is noted as invasive in Florida, but have not shown to be in California. Senna didymobotrya may be another species yet deemed to be invasive in California, as it is already invasive in Eastern Africa, and has the potential to become invasive in South Africa and Australia, which have similar climates to southern California.

Silver senna is found in the southwestern United States, in a climate that matches that of its native range. Plants are also found in southwestern Asia, southwestern Europe, and north and south Africa.

Silver senna has the potential to become invasive, but not to the extent as other Senna species (University of Arizona 2021). Silver senna is listed as an invasive plant by Saguaro National Park.

Most sources suggest that silver senna is mostly grown as ornamental, but silver senna is listed as an invasive plant to Saguaro National Park. It is implied that invasive plants such as silver senna may contribute to promoting changes fire regimes where it displaces native vegetation. Silver senna is listed as a "fire retardant" plant by the Indigenous Landscape Design Australia website, where it is encouraged to be planted as an ornamental plant.

The University of Arizona's Desert Legume Program notes that cattle graze on Senna artemisioides in Australia, where it is native, and grows in inland desert, grassland, and woodland habitats.
Other Senna species may affect humans or animals/fish: Senna occidentalis is toxic to humans, causing liver failure (Ish et al. 2019). Senna occidentalis, Senna roemariana, Senna lindheimeriana, and Senna obtusifolia are noted as toxic to livestock and goats (Fannin 2015, Pfeifer 2018, Ish 2019, Texas A & M 2023).

There is not enough information available to answer this question accurately. However, it is noted that silver senna will grow fast and large when excessively irrigated.

There is not much evidence showing that this species reproduces and spreads vegetatively. Silver senna mostly grows from seed.

Most sources suggest that silver senna mainly produces new plants from seeds, but does not naturally reproduce from plant fragments. Cuttings may continue to grow in a greenhouse before being planted in the ground, but not in natural settings (Secuianu 2019).

Silver senna mainly reproduces and grows from viable seed. Seeds can readily germinate after being treated with boiling water (Australian Native Plants Society 2022). Seeds can also germinate after scarification treatments.

Silver senna produces abundant seedpods and hundreds of viable seeds, according to one source, the Australian Native Plants Society (Howes 2009).

Seeds can germinate after scarification treatments, but Senna artemisioides ssp. x coriacea (Benth.) Randell scarified seeds germinate at a slower rate in cooler temperatures (Pound et al 2015).

Silver senna flowers January through May, and may produce seed after flowering. It is unknown whether seeds are viable within the first 3 to 5 years.

Silver senna flowers January through May, potentially producing seed through those months. It may be uncommon for silver senna to produce seed outside of its flowering period, but it may be possible in irrigated garden settings.

Seeds may be dispersed by cattle (stuck on hooves) in natural settings, where plants are growing in or nearby grazed pastures/grasslands in their native range.

Seeds may be dispersed by wind or water, but it is not confirmed how often or frequent seeds are dispersed long distance. With large flooding events, it can be estimated that once or twice a year seeds may be dispersed great distances.

Sources suggest that silver senna seed is dispersed by people (planting in gardens) and wind, water, and some animals in natural settings.