Searsia lancea -- Arizona

Searsia (Rhus) lancea has been documented as naturalized in sites around Phoenix and Tucson, Arizona. Flora of the Papago Park Military Reservation [Phoenix, AZ] (Walters, 2021). Lists: Rhus lancea. Rhus lancea apparently colonized the study site (Desert Laboratory, Tumamoc Hill, Tucson, AZ) after 1983 (Bowers et. al 2006).

The species has a moderate to high invasive potential in urban areas and surrounding riparian habitats. Basically, seedlings can germinate anywhere there is constant or seasonal sources of water (Martin, 2021). This commonly cultivated shade tree is quite invasive and can now be found growing wild in washes and along canyon streams in the deserts around Tucson (Kinsey, 2021).

Online herbarium specimen records further clarify occurrences in the Phoenix and Tucson areas:

Herbarium specimen: Locality: USA, Arizona, Maricopa, Cave Creek; 'Jewel of the Creek' at Spur Cross Ranch,
Desert Foothills Land Trust; just upstream of where hiking trail crosses the creek; small
ephemeral wash coming in from the east. 33.8917 -111.95214 WGS84 Elevation: 710 meters Verbatim
(SEINet, 2021 2021. http//:swbiodiversity.org/index.php. Accessed on June 14)

Herbarium specimen: Locality: United States, Arizona, Maricopa, N side of South Mountain Park, Phoenix
33.3555 -112.065 Verbatim Coordinates
(SEINet, 2021 2021. http//:swbiodiversity.org/index.php. Accessed on June 14)

Herbarium specimen: Locality: U.S.A., Arizona, Pima, Major drainage running parallel to Sweetwater Trail,
Tucson Mountains, Saguaro National Park
32.2700572 -111.13383241 +-5m. NAD83
Elevation: 1040 meters Verbatim Elevation: 3400 ft.
Habitat: Rocky bank of drainage
Substrate: Gravelly soil
Associated Species: Encelia farinosa
Description: One small sapling, maybe 0.75 m. tall
Reproductive Condition: Non-reproductive
Notes: Likely introduced by a bird. Cultivated plants noted in adjacent neighborhood.
(SEINet, 2021 2021. http//:swbiodiversity.org/index.php. Accessed on June 14)

Searsia lancea is documented as naturalized in California. A catalogue of 315 non-native vascular plant taxa documented as occurring spontaneously in beyond those addressed in The Jepson Manual: Higher Plants of California is presented, compiled from new collections by the authors and others, previously existing herbarium formal publications, other printed reports, and direct communications with field botanists. Rhus lancea listed as Naturalization class N: naturalized (outside of wetlands). (Hrusa et. al. 2021).

Searsia lancea is documented as naturalized in India. Negi & Hajra (2007) list Rhus lancea as an exotic of the Doon Valley.

Searsia lancea is documented as naturalized in Australia, in far western New South Wales (WeedWise, NSW, 2018).

Searsia lancea has a wide distribution across southern Africa (Stern, 2008). There is a climate match between much of Arizona and a portion of South Africa, shown by GBIF. Searsia lancea is naturalized in the Sonoran Desert region of California; Coachella Valley, Palm Springs (Hrusa et al. 2002). There is a probable PRE combined match with the Doon Vally in northern India (Negi et al. 2007), as well as western New South Wales in Australia (WeedWise, NSW, 2018).

This species generally occurs as a weed in wildland areas of the Southwestern Region [USA] rather than as an invasive plant. (USDA, 2021). The species is not listed in the Global Invasive Species Database website (GISD).

This species generally occurs as a weed in wildland areas of the Southwestern Region [USA] rather than as an invasive plant. (USDA, 2021). The species is not listed in the Global Invasive Species Database website (GISD).

Most of the species formerly belonging to the genus Rhus native to southern Africa have been placed in Searsia. In southern Africa there are about 111 species of Searsia (Stern, 2008). No Searsia or Rhus, other than S. lancea, are known to be naturalized in the USA (USDA Plants Database, 2021). The Global Compendium of Weeds lists no Searsia, but does list various Rhus species. Rhus transvalensis is listed, with reference to Wells (1986) but it is treated as an agricultural weed in its native Africa, which does not convey invasiveness. There is no evidence of other Searsia being invasive in a similar climate.

Searsia lancea has a wider natural range in southern Africa than the PRE Combined map shows (GBIF, 2021). Most of the naturalized occurrences shown in GBIF correspond with regions in the PRE combined map, particularly southern Arizona and southern California. Although not shown in GBIF, the documented occurrence in Doon Valley in northern India (Negi et al. 2007) appears to match the PRE combined map. Also apparently matching the PRE combined map is the western part of New South Wales, Australia (WeedWise, NSW, 2018).

It can displace mesquites (AZNPS, 2021). In New South Wales it is outcompeting native plants (WeedWise, 2018).

Listed as a volatile woody fuel (Goldammer & de Ronde, 2004). Searsia lancea has been investigated as a combustible biomass resource, and is observed to ignite at low temperatures (in the range 220–250 °C) (Ndou et al. 2020). The species has the ability to resprout from the base (International Dendrology Society, 2021).

The species is wind-pollinated and it is reported some people find African sumac to be a source of allergies due to the pollen from male flowers during desert winters (Martin, 2021). Abundant allergy-producing pollen (Steller, 2021). However there are no reports of these allergies being severe.

Listed by (Wells, 1986) as having undesirable characteristics: contaminant: seed. But the seed is not reported as poisonous. The leaves and fruit are eaten by wild animals and livestock (Stern, 2008).

Searsia lancea is suitable for use as a large hedge along the boundaries of properties such as farms because of its dense growth habit. The density of the plant makes it suitable for use as a screen or barrier against wind, noise, objectionable views or to provide privacy (Stern, 2008).

It spreads by suckers (Breen, 2021). It can sucker from the roots (WeedWise, 2018). However, the suckering habit is not mentioned in publications from its native habitat in southern Africa.

No evidence of vegetative spread other than suckering from the base. The tree may be propagated easily from seed, cuttings or layers (Stern, 2008) but this discussion of propagation makes no mention of naturally detached fragments.

Searsia lancea can be propagated easily from seed, cuttings or layers. The ripe seed should be sown in seedling trays using a good seedling medium and transplanted into bigger containers when the seedlings reach the two-leaf stage (SANBI, 2021)

African sumac has a moderate to high invasive potential in urban areas and surrounding riparian habitats. Basically, seedlings can germinate anywhere there is constant or seasonal sources of water (Martin, 2021).

HEAR evaluation (2021) considers Searsia a relatively prolific seed producer and sprouts from basal stems and roots...Dense infestations produce >1,000 viable seed per square meter [answered "No"]. The "NO" rating taken to mean HEAR suggests it does not produce >1,000 viable seeds. HEAR provides a source link, but the original data could not be found from the linked site. Considering a large tree comprises many square meters of branches, however, I believe this can still be answered Yes, with low confidence.

Searsia lancea can be propagated easily from seed, cuttings or layers. The ripe seed should be sown in seedling trays using a good seedling medium and transplanted into bigger containers when the seedlings reach the two-leaf stage (SANBI, 2021)

Basically, seedlings can germinate anywhere there is constant or seasonal sources of water (Martin, 2021).

Growth rate is said to be fast when young, to 1m per year (Carr et al. 1986). Plants might have potential to reach flowering size in five years. Plants are dioecious, which could have relevance (White, 2013).

Flowers June to September; dioecious; female plants bear small (less than 1/8 inch long), greenish-white flowers in panicles; open panicles 3/4 to 3-1/2 inches long (shorter than the leaves) (USDA, 2021).

The fruit is eaten by birds (Stern, 2008), which would have the potential to spread seeds over 100 m from the source.

The karee occurs naturally in Acacia woodland and along drainage lines, rivers and streams (Stern, 2008). Searsia lancea is most noticeable in arid areas near water although it roots do no not penetrate as deep. It therefore grows closer to water (Becking, 2021). Although proximity to water might facilitate the dispersal of seeds, the fruit is described as a small one-seeded drupe (Becking 2021) with no obvious adaptations for water dispersal.

Listed by (Wells, 1986) as having undesirable characteristics: contaminant: seed. However no context is stated.

Fruit: Small (up to 3/16 inch diameter), round, slightly flattened yellow or red wrinkled drupes grow in clusters; fruit contains small black seeds (USDA, 2021). The fruit and seed have no obvious structures for mechanical dispersal (Becking, 2021).