Zinnia peruviana
(Peruvian zinnia)

Zinnia peruviana is a subtropical and tropical, fast-growing, annual herb of American origin. It occurs in gardens, roadsides, disturbed places, wastelands and pastures. It was listed in the Global Compendium of Weeds (Randall, 2012) as a naturalized agricultural and environmental weed, casual alien and cultivation escape. It is a weed in parts of America including Mexico and Ecuador, where it is native. It is also a weed and an escape from cultivation in other parts of the world such as the Galapagos Islands, Queensland in Australia, China, Swaziland and Ethiopia. In South Africa it was reported as one of the top 28 invasive species in the Kruger National Park. A weed risk assessment for Hawaii concluded that further evaluation was necessary to determine whether the species is invasive there.

Z. peruviana is the only species of the genus with a native range that extends outside North America. The three species of subgenus Zinnia section Zinnia have their centre of origin in the Sierra Madre Occidental, Mexico at elevations from 900 m to 3000 m above sea level. Aside from the mountainous region of Mexico, it is also found in “large uniform populations along the roadsides”, “along which sheep, burros [donkeys], cattle and dogs frequently move” (Torres, 1963).

Although Z. peruviana is native to the Americas, it is not prevalent everywhere. For example, it was not listed in work carried out by Funk et al. (2007) on the Guiana Shield and is reportedly uncommon in Nicaragua, where specimens have been collected from the western side of the country’s mountainous region (Flora of Nicaragua, 2016).

There are some discrepancies in reports of the native status of Z. peruviana. In the Caribbean, the species has been introduced and is naturalized in Puerto Rico (Acevedo-Rodríguez and Strong, 2012), but the USDA-NRCS (2016) reports it as native to Puerto Rico as well as the continental states of the USA. However, the USDA-ARS (2016) records this species as naturalized in all of these locations except Arizona in the USA, where it is native.

Z. peruviana is naturalized and in some places is weedy or invasive in eastern Australia, Hawaii and parts of French Polynesia. However, the species does not have a significant presence in the Asia-Pacific region, suggesting it may remain confined to ornamental cultivation. It was not included in the Smithsonian Flora of Micronesia (Wagner et al., 2016) or Flora of the Marquesas Islands (Wagner and Lorence, 2016), although the related species Z. violacea is reported in these places. Neither was it included in work by Chong et al. (2009) on Singapore, Kress et al. (2003) on Myanmar or Leonard Co’s Flora of the Philippines (Pelser et al., 2016).

The Global Compendium of Weeds (Randall, 2012) categorizes Z. peruviana as a cultivation escape and an environmental, agricultural and disturbance weed. In its native range, the species is a common, but rarely dominant, weed (CONABIO, 2017). However, the species is invasive in parts of Ecuador, eastern Australia, French Polynesia and Hawaii (PIER, 2016; Weeds of Australia, 2016). Since the 18th century, it has been repeatedly introduced to places beyond its native range due to its continued popularity as an ornamental species. Its invasive traits include seeds that are adapted for wind and animal dispersal, a relatively short generative time of one year, tolerance of a range of soil types, the ability to grow in heavily disturbed areas and the ability to thrive in tropical climates (Torres, 1963; Johnson and Kessler, 2007; PlantPono, 2014). Traits that lower its potential as an invasive species include non-toxicity, a requirement for full sun and well-drained soil and an inability to regenerate vegetatively (Johnson and Kessler, 2007; PlantPono, 2014). Considering these factors, the risk of introduction for this species is medium, but further evaluation is required.

Z. peruviana in its natural habitat occupies mountain slopes and valleys, woodlands and grasslands. In addition to these, it is a common weed in disturbed areas, rocky roadsides, ravines, particularly growing on calcareous soils, from 1200-1600 m above sea level.

In Peru, where it is native, samples of the species have been collected from the Amazonian, coastal and lower Andean parts of the country, up to 3500 m (Peru Checklist, 2017). In the Andean lowland regions of Bolivia, the species grows up to 3000 m in semi-deciduous forest, secondary forests, abandoned fields and dry valleys (Bolivia Catalogue, 2017). It has also been reported in Madidi National Park in the upper Amazon river basin (Madidi Checklist, 2017). Specimens have also been collected in northwestern Paraguay, near the Bolivian border (Paraguay Checklist, 2017). In parts of China where it was cultivated and has naturalized, the species has been found up to 1300 m (Flora of China Editorial Committee, 2017).

Genetics

Z. peruviana is diploid with a chromosome number of 2n = 24 (Torres, 1963).

Reproductive biology

Z. peruviana florets are pollinated by bees and flies and are visited by hummingbirds. Although it is usually an outcrossing species, it is self-compatible (Torres, 1963).

Environmental requirements

Z. peruviana requires full sun to light shade and several days of moderate water availability to grow. The plant favours neutral to slightly alkaline soils and can tolerate all soil types except for wet, poorly aerated soils, which can cause root rot (Johnson and Kessler, 2007).

Z. peruviana is susceptible to insects such as aphids, thrips and whiteflies, as well as horticultural diseases such as Alternaria zinniae (alternaria leaf spot), Botrytis cinerea (botrytis blight), Xanthomonas campestris pv. zinniae (bacterial leaf spot) and Golovinomyces cichoracearum var. chichoracearum (powdery mildew) (Johnson and Kessler, 2007).

General

• Botanical garden/zoo
• Sociocultural value

Medicinal, pharmaceutical

• Traditional/folklore

Ornamental

• Cut flower
• Potted plant
• Seed trade

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical Control

Members of the Zinnia genus can be controlled or weakened by chemicals and nutrient adjustment. Certain pesticides burn Zinnia leaves and excess soil nitrogen levels lead to weakened stems (Johnson and Kessler, 2007).

Biological Control

The invasiveness of Z. peruviana in a disturbed habitat may be facilitated by overgrazing (PlantPono, 2014). In a case report from Pretoria, South Africa, van Hoven et al. (2009) identified Z. peruviana as an alien invasive plant species that influences the occurrence of palatable grasses. They reported that Z. peruviana “should be outcompeted by grasses once overgrazing has been minimised”. This information may be useful for biological control in certain situations.

Z. peruviana has been reported as invasive in some parts of the world, but there is little data regarding the extent of its potential ecological, economic or social impacts. Due to its use as an ornamental, this species will continue to be introduced around the globe. Considering this, and the invasive traits of this species, further risk assessment is needed.

30/03/17 Updated by:

Marianne Jennifer Datiles, Department of Botany-Smithsonian NMNH, Washington DC, USA

Original text by:

Christopher F Puttock, Department of Botany-Smithsonian NMNH, Washington DC, USA