Euphorbia bourgeana -- California

Euphorbia bourgeana (tree Euphorbia; also known as E. bourgaeana and including synonomy with E. lambii) is native to the Canary Islands (Tenerife and San Sebastian de la Gomera) where it has a limited distribution and is considered vulnerable (IUCN 2025). It is a large shrub with attractive terminal foliage and stem structure that is sold as an ornamental. E. bourgeana is reported as occurring in ornamental landscapes in New Zealand. This plant has been observed to prolifically seed and grow from seed in landscaped areas in landscaped yards in Encinitas and San Marcos CA as well as the San Diego Botanic Garden. It has also been observed in disturbed/waste areas (J. Giessow, person. obs.), however its naturalized status is unknown there.

Although E. bourgeana appears to tolerate and grow well in climates that match California both in its native range and where it has been planted, it has not been verified as being naturalized outside of its native range. The climate match map shows that California and New Zealand share climate with the Canary Island. GBIF reports location in California and New Zealand, though it is unclear if these were naturally established and persistent. It reports another location in Sweden, which is likely the miscoded location of a plant collection or herbarium. San Marcos Growers in California reports that this species does volunteer in some landscaped environments but it does not indicate that it has naturalized.

There is no evidence to date of E. bourgeana having become invasive anywhere in the world. It is reported as a "casual alien" only New Zealand by Randall (2017).

Euphorbia bourgeana has not been reported as being invasive in any environment. However, the it is reported to be aggressively volunteering from ornamental plantings in southern California (J. Giessow, pers. obs).

There are several other species in the genus Euphorbia that are known to be invasive in a similar climate and in California. Euphorbia terracina (leafy spurge) is listed by CABI as invasive in South Africa and California (where is is listed by both Cal-IPC and CDFA). Other examples are provided by Randall (2017). In addition to E. terracina, several other Euphorbia species are listed in the California Invasive Plant Council's inventory: these include Euphorbia lathyris, E. myrsinites, E. oblongata, and E. virgata.

According to the climate match map, the known similarity in climate of the Canary Islands to that of southern California, and the restricted distribution of this species, most of the known occurrences of this species occur within climate that matches California.

There is no documentation of E. bourgeana overtopping and dominating the native plant community. This species is a large shrub but has an open canopy structure. It is considered vulnerable in its native range due to its restricted distribution. There, it occurs in open forests and shrublands and does not appear to form monocultures (see IUCN 2025).

There is no evidence of this species promoting or changing fire regimes. IUCN lists fire as a threat to it in its native range. It produces large, broadly linear leaves that are semi-persistent (Barres et al., 2017), but these do not appear to create significant fuels. As larger-statured shrub, stems, when healthy, remain live and do not die back.

All Euphorbia have a latex sap that is toxic to wildlife and humans. It is not known to impact grazing systems where it currently grows.

Based on this species open canopy architecture, it does not produce impenetrable thickets.

Euphorbia bourgeana is a shrub that appears to reproduce primarily from seed. Although it is propagated via cuttings in the ornamental industry, there is no evidence that it either sprouts from roots or from stem fragments in the wild.

There is no evidence that vegetative propagation is a common method of reproduction for Euphorbia bourgeana. Existing literature does not list this species as having vegetative propagation.

Since this species can flower prolifically and does not apparently reproduce vegetatively, by deduction it produces viable seed. The IUCN report on it does not indicate that inbreeding or pollinator availability are threats; rather, it suggests that human disturbance and habitat loss are primary threats to its survival. San Marcos Growers reports that it volunteers from seed in some landscaped environments. Young plants have been observed recruiting from established plants every year in areas where mature plants occur in landscaping. Photos provided by J. Giessow (see species page).

No published data available on seed production, however observation data supports a "yes" for this answer. Each fruit has the potential to contain up to three seeds, but there is no documentation for how successfully it fruits and how many fruits are produced per mature plant. Field observations by J. Giessow suggest that a mature plant has from 1-200 branches (averaging around 10); each branch produces 5-20 seed pods, each of which can contain three seeds. Therefore, an average plant would be expected to produce ca. 300 seeds. However a very large plant could produce up to 12,000 seeds. Based on the distribution of seedling volunteers around mother plants, seeds disperse about 10'.

Observers have noted that Euphorbia bourgeana has recruited from seed at San Diego Botanical Garden (J. Giessow, pers. comm.). San Marcos Growers (Santa Barbara County) have reported that seedlings readily sprout under mature shrubs.

Although a nursery website mentions that this woody species grows quickly, no direct information was found on how long it takes to grow from seedling to maturity. Observations by J. Giessow are that plants produce seed in 3-4 years, but that plants are still small at this age, typically only with one or a few stems/branches.

At least one nursery website states that this shrub flowers "from late winter to mid spring". iNaturalist records from its native range in the Canary Islands, show blooming from February through June. Therefore, there is some evidence that this species blooms and sets seed for a longer period than three months. Seed pods develop and then dry on plant, dehiscing in late summer/fall.

No evidence was found that E. bourgeana seeds disperse long distances mammals or birds. Its seeds are not known to be attractive to birds. J. Giessow reports that seedpods dehisce explosively, propelling seed up to 10'. No mammals or birds have been observed moving seeds further or eating seed.

Given that this species has a very restricted island distribution and that populations on neighboring islands have apparently been isolated enough to be at times considered different species, it is unlikely that this species disperses effectively by wind or water. It is also not known to have propagules that float. It does not grow along waterways but rather is restricted to shrubby or sparsely wooded slopes in its native range.

Given that this species is rare in its native range and currently only occurs where it has been planted in landscaping, it is safe to presume that it is not frequently dispersed as a contaminant.