Erythrostemon gilliesii -- Arizona

Erythrostemon gilliesii is native to areas of Argentina and Uruguay where it occurs in savanna and woodland habitats. Widely planted in the southwestern U.S. and sometimes naturalizing in areas with sufficient rainfall (DELEP, 2021). The plant is noted in regional floras for Arizona (Carnahan & Davis, 2020)(Roll, 2020). The USDA Plants Database (USDA, 2021) shows E. gilliesii occurring in California, Nevada, Utah, Arizona, New Mexico, Texas, Georgia and Puerto Rico. In South Africa, E. gilliesii is classified as a 1b = invasive species that must be controlled in accordance with a national management programme, and cannot be traded or otherwise allowed to spread (Williams et al, 2021). The plant is introduced in the Canary Islands (Verloove, 2017), the Iberian Peninsula of Spain (Aymerich & Saez, 2019), Italy (Stinca, 2021), Libya (Saaed et al, 2021), Sardinia (Puddu et al, 2016), Chile (Santilli, 2018), Mexico (Ruida-Torres et al, 2022) (Castillon et al, 2005), and most of the states in Australia (McCune, 1998).

In addition to being naturalized in Arizona, Erythrostemon gilliesii is naturalized in the following regions which are a climate match for Arizona: California, Nevada, Utah, New Mexico, Texas (USDA, 2021) South Africa (Williams et al, 2021); the Iberian Peninsula of Spain (Aymerich & Saez, 2019); Chihuahua, Mexico (Ruida-Torres et al, 2022) Nuevo Leon, Mexico (Castillon et al, 2005); and most of the states in Australia (McCune, 1998).

Although naturalized in many parts of the world, Erythrostemon gilliesii is typically described as a cultivation escape, environmental weed, garden thug, naturalized, or weed (Thomas, 2017). Evidence of impact is listed as "No" by GBIF (2022). The Plant has not been documented reaching the level of impact to meet the definition of invasive used by the PRE. The plant is listed as a NEMBA Category 1b plant by South Africa Invasives. The NEMBA Categories are regulatory categories, with this listing indicating the species must be controlled (SA Invasives, 2021). The fact sheet provided by South Africa Invasives does not elaborate on the impact or characteristics of Erythrostemon occurrence in the country. It is uncertain whether this meets the definition of invasive used by the PRE.

Although naturalized in many parts of the world, Erythrostemon gilliesii is described as a cultivation escape, environmental weed, garden thug, naturalized, or weed (Thomas, 2017). This includes occurrance in regions with a similar climate to Arizona, but there the plant has not been clearly documented to reach the level of impact to meet the definition of invasive used by the PRE.

Erythrostemon is a small genus previously classified in the formerly large genus Caesalpinia. The Global Compendium of Weeds (CABI, 2007) lists this species under Caesalpinia. It also lists Caesalpinia decapetala as invasive for climate-matching regions of Australia and South Africa. Caesalpinia spinosa is naturalized to climate-matching regions of California, but not known to be invasive there (Wojciechowski & McClintock, 2012).

Apparently more than half of the places the plant is native or naturalized are within the climate match map for Arizona.

Said to compete with indigenous vegetation in South Africa (SA Invasives, 2021). The naturalized occurrence of the shrubs are usually sporadic in distribution and the plant possess a wide, open branching structure unlikely to shade out other plants (personal observation in the southwest USA, also see photos on Calflora, 2022).

No published information on fire effects was found. The sporadic occurrence of the naturalized plants, without forming dense stands (personal observation in the southwest USA) suggests a low potential to carry wildfire.

The seeds and the green seed pods of this plant are toxic, provoking severe vomiting and other abdominal symptoms (SA Invasives, 2021). The green fruits and seeds of this species can cause gastrointestinal upset if eaten (DELEP, 2021). Toxic to cats and dogs (Gardenia.net, 2022). The first two references would seem to refer to toxicity to humans, while the latter reference is to toxicity to pets.

The naturalized occurrence of the shrubs are usually sporadic in distribution and possessing a wide, open branching structure (personal observation, also see photos on Calflora, 2022).

No information available suggests natural vegetative spread. The character of the plant does not suggest the likelihood (personal observation).

No information available suggests natural vegetative spread. The character of the plant does not suggest the likelihood (personal observation).

Plants can volunteer from seeds in locations where there is sufficient moisture and sometimes spread into natural areas (DELEP, 2021). Propagate by seed or softwood cuttings (Gardenia.net, 2022).

The plant is a shrub with a low to moderate number of flowering branches (personal observation). Fruits are legumes containing a limited number of seeds. Seeds are large, 9mm in length (Kheloufi et al, 2018) and must be produced in smaller numbers than tiny seeds would. By inference, not a copious seed producer.

A germination trial recorded 82.5% germination of untreated (control) set of seeds (Kheloufi et al, 2018).

It is reported to be fast growing (Gardenia.net, 2022). Being a shrub, by inference it is possible it can reach a reproductive state within five years.

Flowering Period: Almost throughout the year, at least in Karachi (Anonymous, 2022). Flowering extends from spring into autumn (DELEP, 2021).

The plant's reported toxicity and dry dehiscent seed pods (Gardenia.net, 2022) count against the likelihood of seed dispersed by ungulates. The large size of the seeds (Kheloufi et al, 2018) makes them unlikely to be dispersed in the crop of birds. The seed pods dry and split, sometimes explosively (Gardenia.net, 2022) suggesting a mechanical means of short-distance seed dispersal.

Seeds are large and smooth (Kheloufi et al, 2018) with no obvious adaptation for traveling by wind or water.

The seed pods dry and split, sometimes explosively (Gardenia.net, 2022) suggesting a mechanical means of short-distance seed dispersal. The occurrence of the plant along roadsides suggests the seeds might be moved in the tread of vehicle tires. However, no information is available on how the plants seeds are dispersed over long distances to reach remote areas.