Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Pelargonium zonale
(horseshoe pelargonium)



Pelargonium zonale (horseshoe pelargonium)


  • Last modified
  • 19 November 2018
  • Datasheet Type(s)
  • Documented Species
  • Preferred Scientific Name
  • Pelargonium zonale
  • Preferred Common Name
  • horseshoe pelargonium
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • P. zonale is a flowering plant native to South Africa that has been cultivated as an ornamental in tropical and subtropical parts of the world. The species is listed in the Global Compendium of Weeds as “garden...

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Preferred Scientific Name

  • Pelargonium zonale (L.) L'Hér. ex Aiton

Preferred Common Name

  • horseshoe pelargonium

Other Scientific Names

  • Ciconium densiflorum Eckl. & Zeyh.
  • Geranium zonale L.

International Common Names

  • French: géranium à feuilles zonées

Local Common Names

  • Cuba: geranio manzana
  • Italy: geranio zonale
  • Netherlands: rundbladet pelargonie
  • Puerto Rico: geranio; geranium
  • South Africa: wilde malva

Summary of Invasiveness

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P. zonale is a flowering plant native to South Africa that has been cultivated as an ornamental in tropical and subtropical parts of the world. The species is listed in the Global Compendium of Weeds as “garden thug, naturalised, weed” (Randall, 2012), is known to escape from cultivation (Liogier and Martorell, 2000), and some of its hybrids are known to be weedy or invasive, but it does not appear to be a Pelargonium species with high risk of introduction based on current evidence.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Geraniales
  •                         Family: Geraniaceae
  •                             Genus: Pelargonium
  •                                 Species: Pelargonium zonale

Notes on Taxonomy and Nomenclature

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There has been much confusion in the literature surrounding the genera of Pelargonium and Geranium. The genus Geranium was originally described by Linnaeus in 1753 but was then divided into Pelargonium and Geranium by Charles L’Héritier in 1789, and many species from both genera have retained the name ‘geranium’ in their vernacular names. Further, many cultivars and varieties exist, many with similar variety names to other species. The genus name Pelargonium derives from the Greek word ‘pelargos’, meaning ‘stork’, in reference to the beak-like shape of the fruit, which has also resulted in the genus being called the ‘stork’s bill’ genus (Stearn, 1992).

The genus Pelargonium is divided into sections based on morphological and other features. The species Pelargonium zonale is a member of the Ciconium section. P. zonale is the parent of many, if not most, ornamental hybrids, such as the popular P. x hortum, the common garden pelargonium (Miller, 1996; SANBI, 2014). The species name zonale is derived from the Latin word ‘zona’, meaning ‘banded’ or ‘with a girdle’, referring to the horseshoe marking found on its leaves (Stearn, 1992; Miller,1996; SANBI, 2014). 


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Erect, softly woody shrub or subshrub. Usually grows up to 1 m (40 in) but can reach heights of 3 m, often found scrambling through bushes or cascading off cliffs. Young branches almost succulent and usually covered with hairs, harden with age. Leaves orbicular, crenate, often with a characteristic, dark, brownish-purple, horseshoe-shaped mark. Flower colour usually pale pink, sometimes white or red, or a range from rose-pink to all shades of red, buds reflexed. The distinctly irregular flowers are borne in a typically umbel-like inflorescence (Walt, 1977; Miller, 1996; SANBI, 2014).


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P. zonale is widely distributed in its native South Africa, and is reported to be cultivated as an ornamental in various parts of the world including Bolivia, Colombia, Myanmar, various parts of Europe, parts of the West Indies, and the United States (Wiersema and Leon, 1999; Kress et al., 2003; Acevedo-Rodriguez and Strong, 2012; Bolivia Checklist, 2014; Royal Botanic Garden Edinburgh, 2014; Flora of Pakistan, 2014; ITIS, 2014; SANBI, 2014; Vascular Plants of Antioquia, 2014). The Distribution Table does not cover all places where it is cultivated, as it is not listed in the floras of some countries where it is present in cultivation.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


MyanmarPresentKress et al., 2003
PakistanPresent only in captivity/cultivationIntroducedFlora of Pakistan, 2014


South AfricaPresentNativeUSDA-ARS, 2014Cape province

North America

USAPresentPresent based on regional distribution.
-CaliforniaPresentIntroducedUSDA-NRCS, 2014

Central America and Caribbean

Dominican RepublicPresentIntroducedAcevedo-Rodriguez and Strong, 2012‘exotic’
HaitiPresentIntroducedAcevedo-Rodriguez and Strong, 2012‘exotic’
Puerto RicoPresentIntroducedLiogier and Martorell, 2000; Acevedo-Rodriguez and Strong, 2012; USDA-NRCS, 2014
Trinidad and TobagoPresent only in captivity/cultivationIntroducedPrestoe, 1870

South America

BoliviaPresent only in captivity/cultivationLa Paz
ColombiaPresent only in captivity/cultivationVascular Plants of Antioquia, 2014Donmatías, Medellín, Titibirí


FrancePresentIntroducedDAISIE, 2014‘alien’, ‘established’
ItalyPresentIntroduced Not invasive DAISIE, 2014‘alien’, ‘not established’ in mainland Italy, Sardinia, Sicily
SpainPresentIntroducedDAISIE, 2014‘alien’, ‘established’

History of Introduction and Spread

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P. zonale is native to South Africa but is a common ornamental flowering plant in various parts of the world today. Date of introduction to the West Indies region is unknown; it may have occurred sometime in the late nineteenth century, although ornamental hybrids may have been introduced earlier. The species was reportedly being cultivated in Trinidad in 1870 (Prestoe, 1870), and both Britton’s 1918 flora of Bermuda (1918) and Britton and Wilson’s flora of Puerto Rico and Virgin Islands (1923-1926) reported that many hybrids of P. zonale were common cultivated garden plants in these places. The species was not included in Macfadyen’s work on Jamaica (1837), Bello’s work on Puerto Rico (1881; 1883), or Britton and Millspaugh’s Bahama Flora (1920). Today the species is an introduced cultivated plant in Puerto Rico and is known to sometimes escape, usually in the mountains (Liogier and Martorell, 2000; ITIS, 2014).

P. zonale was reportedly introduced to Europe at the turn of the eighteenth century by way of the Netherlands, where the garden in Leiden received seeds from the garden of the Dutch East India Trade Company in South Africa, and the plant was recorded to be growing in Amsterdam’s medicinal gardens by 1700 (Miller, 1996). Another source places this introduction a full century earlier in 1609, when a shipment apparently arrived from South Africa’s Cape colony to the Netherlands, but this is unlikely (Loewer, 2004). It was first cultivated in England by the Duchess of Beaufort between 1706 and 1710 (Walt, 1977; Miller, 1996). Presumably after 1700 the species was accidentally introduced to the wild in Spain and France where it was being grown as an ornamental, and it has since become established in parts of both countries (DAISIE, 2014). In Italy it was accidentally introduced through live “food trade, animals and plants used for ornamental purposes in parks, gardening, bonsai, etc.”, but reportedly did not become an established introduction in the country (DAISIE, 2014). In Sardinia and Sicily, the species was also accidentally introduced but likewise has not become established (DAISIE, 2014). The species remained popular throughout eighteenth century Europe, and in 1801 Rembrandt portrayed his botanist brother Rubens holding a large geranium in a terracotta pot. It was arguably during Victorian Britain that the cultivated geranium reached the height of its popularity, and the flower was a common feature in nosegays and poppies used to convey messages to one another through the ‘language of flowers’ that had been popularized during this time.

In the USA, P. zonale has been present in cultivation since at least the time of Thomas Jefferson’s presidency (1801-1809), as he had the plant growing at both the White House and his home in Virginia, Monticello (Loewer, 2004). In California today, the species is a known introduction and reportedly “to be treated as a waif, in part because of an apparent lack of evidence that the plants are naturalized in CA” (ICPN, 2014). The species was reportedly present in Hawaii by 1888 (Stone et al., 1992), but less data is available for this species in the Pacific and Asian region than other Pelargonium species and hybrids.

Risk of Introduction

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Risk of introduction for this species appears to be low, as it has been imported to Europe and other parts of the world for some time and has not yet been reported to be a high threat. However, many Pelargonium hybrids have resulted from breeding programmes involving P. zonale, and some of these are now known to be weedy or invasive. It is included but not listed as invasive in the Global Compendium of Weeds (Randall, 2012) and does not appear to be a priority species in the Pacific, as it has not yet received a PIER risk assessment. The risk of introduction of this species is thus currently low, but considering it is a Pelargonium and that it is repeatedly cultivated beyond its native range of South Africa, monitoring may become necessary in the future, particularly in places where it is known to be established or to have escaped from cultivation.


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In its native South Africa, P. zonale is common in coastal areas, and grows naturally in valleys and ravines, on forest margins, cliffsides and rocky outcrops with scrub vegetation (Walt, 1977; SANBI, 2014). The species also occurs in dry valleys of the Bolivian Andes (Bolivia Checklist, 2014) and is widely cultivated in most tropical countries or in greenhouses (Flora of Pakistan, 2014).

Habitat List

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Terrestrial – ManagedProtected agriculture (e.g. glasshouse production) Present, no further details Productive/non-natural
Urban / peri-urban areas Present, no further details Productive/non-natural
Terrestrial ‑ Natural / Semi-naturalNatural forests Present, no further details Natural
Natural forests Present, no further details Productive/non-natural
Rocky areas / lava flows Present, no further details Natural
Scrub / shrublands Present, no further details Natural
Coastal areas Present, no further details Natural

Biology and Ecology

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Gametophytic count = 9,15; sporophytic count= 15, 24 (IPCN Chromosome Reports, 2014).

Environmental Requirements

In cultivation, Pelargonium species can be grown in borders or containers, can tolerate soils with pH ranging from neutral to alkaline, and prefer well-drained, dry or moist, light (sandy) and medium (loamy) soils (PFAF, 2014). P. zonale usually does best in full sun and is sensitive to shade, but cultivar hybrids of P. zonale may tolerate some shade (PFAF, 2014; Royal Horticultural Society, 2014). 


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BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Means of Movement and Dispersal

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P. zonale has been intentionally introduced by man beyond its native South African range to various parts of the world primarily for cultivation as an ornamental plant. It is also an accidental introduction, as it has reportedly escaped from cultivation in Puerto Rico and the Mediterranean (Liogier and Martorell, 2000; Randall, 2012). Cultivars have also been developed from P. zonale which are likewise widespread in cultivation.

Members of the Pelargonium genus can disperse their small seeds by wind, water, and soil. Their seeds typically possess a plume or tail-like attachment which can carry them over long distances. The attachment on the seeds of P. capitatum, for example, reportedly will essentially drill and secure the seed into soil if twisted by the wind or affected by movement of animals, and this species is considered one of the most widespread and naturally invasive of coastal weeds in the Perth region of Australia (Dixon, 2011; Western Australian Herbarium, 2014). 

Impact Summary

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Environment (generally) Negative

Impact: Environmental

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P. zonale is listed as ‘garden thug, naturalized, weed’ in the Global Compendium of Weeds (Randall, 2012). In Puerto Rico, P. zonale is known to have escaped from cultivation, and is considered weedy in the Mediterranean (Liogier and Martorell, 2000; Randall, 2012). It has not yet demonstrated lasting negative environmental impacts to non-native ecosystems, but considering the severe invasiveness of other genus members, monitoring may be necessary in the future.

Risk and Impact Factors

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  • Abundant in its native range
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Has propagules that can remain viable for more than one year


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The primary reason for this species’ spread to tropical regions around the world is for use as an ornamental flowering plant in botanical gardens, homes, and estates, and it was for this reason P. zonale has been used as a parent species in breeding programs across Europe and America since the eighteenth century (Walt, 1977; Miller, 1996; SANBI, 2014). It also has potential for medicinal use. The species was apparently growing in Amsterdam’s medicinal gardens in 1700 (Miller, 1996), and recent research provides evidence that P. zonale may possess haemostatic and astringent properties (Paez and Hernandez, 2003; PFAF, 2014). Additionally, the leaves of this species are edible and can be eaten as a vegetable (PFAF, 2014).

Prevention and Control

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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.

No information was found for methods of prevention and control of this species, as it has not been reported to be usually problematic. Other Pelargonium species that have proved to be weedy sometimes require government assistance to stop infestations using chemicals, such as the case of P. alchemilloides, which is one of 28 plants listed in Australia’s Federal Government Alert List for Environmental Weeds (CRC for Australian Weed Management, 2003).

Gaps in Knowledge/Research Needs

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Research is lacking on P. zonale’s potential invasiveness in its native South Africa and throughout the Tropics in order to better gauge the risk of introduction and spread of the species, especially in light of the mounting evidence of its medicinal value as a haemostatic agent and given its history as a cultivated ornamental species. Based on the existing literature, risk of introduction of P. zonale is low but not insignificant, as other members of the Pelargonium genus are listed as invasive and potentially harmful to biodiversity and native flora.


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Acevedo-Rodríguez P; Strong MT, 2012. Catalogue of the Seed Plants of the West Indies. Smithsonian Contributions to Botany, 98:1192 pp. Washington DC, USA: Smithsonian Institution.

Bello D, 1883. [English title not available]. (Apuntes para la flora de Puerto Rico. Segunda parte. Monoclamídeas.) Anales de la Sociedad Española de Historia Natural, 12:103-130.

Bello Espinosa D, 1881. [English title not available]. (Apuntes para la flora de Puerto Rico. Primera parte.) Anal. Soc. Española de Hist. Nat, 10:231-304.

Bolivia Checklist, 2014. Catalogue of the Vascular Plants of Bolivia, Tropicos website. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

Britton NL, 1918. Flora of Bermuda. New York, USA: Charles Scribner's Sons. 585 pp.

Britton NL, 1924. Botany of Porto Rico and Virgin Islands. Scientific Survey of Porto Rico and Virgin Islands. New York, USA: New York Academy of Sciences, 200 pp.

Britton NL; Millspaugh CF, 1920. The Bahama Flora. New York, USA: NL Britton & CF Millspaugh.

CRC for Australian Weed Management, 2003. Garden geranium (Pelargonium alchemilloides) weed management guide.

DAISIE, 2014. Delivering Alien Invasive Species Inventories for Europe. European Invasive Alien Species Gateway.

Dixon K, 2011. Coastal plants: a guide to the identification and restoration of plants of the Perth region [ed. by Dixon, K.]. Collingwood, Australia: CSIRO Publishing, x + 277 pp.

Flora of Pakistan, 2014. Flora of Pakistan/Pakistan Plant Database (PPD). Tropicos website St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

ICPN, 2014. Index of California Plant Names. Jepson Flora Project: Jepson Interchange for California Floristics. Berkeley, USA: University of California.

IPCN Chromosome Reports, 2014. Index to Plant Chromosome Numbers (IPCN), Tropicos website. St. Louis, Missouri, USA: Missouri Botanical Garden.

ITIS, 2014. Integrated Taxonomic Information System.

Kress WJ; Defilipps RA; Farr E; Kyi DYY, 2003. A checklist of the trees, shrubs, herbs, and climbers of Myanmar. Contributions from the United States National Herbarium, 45:1-590.

Liogier HA; Martorell LF, 2000. Flora of Puerto Rico and adjacent islands: a systematic synopsis, 2nd edition revised. San Juan, Puerto Rico: La Editorial, University of Puerto Rico, 382 pp.

Loewer HP, 2004. Jefferson's garden. Mechanicsburg, PA, USA: Stackpole Books, 260 pp.

MacFadyen J, 1837. The flora of Jamaica: A description of the plants of that island. London, UK: Longman, Orme, Brown, Green & Longman, 351 pp.

Miller D, 1996. Pelargoniums: a gardener's guide to the species and their cultivars and hybrids. London, UK: B.T. Batsford Ltd, 175 pp.

Pa´ez X; Herna´ndez L, 2003. Topical hemostatic effect of a common ornamental plant, the geraniaceae Pelargonium zonale. Journal of Clinical Pharmacology, 43(3):291-295.

PFAF, 2014. Plants for a future.

Prestoe H, 1870. Catalog of plants cultivated in the Royal Botanic Gardens, Trinidad, from 1865-1870., Trinidad: Chronicle Printing Office.

Randall RP, 2012. A Global Compendium of Weeds. Perth, Australia: Department of Agriculture and Food Western Australia, 1124 pp.

Royal Botanic Garden Edinburgh, 2014. Flora Europaea. Edinburgh, UK: Royal Botanic Garden Edinburgh.

Royal Horticultural Society, 2014. Gardening advice for Pelargonium (geraniums).

SANBI, 2014. South African National Biodiversity Institute plant information website., South Africa: Kirstenbosch National Botanical Garden, South African National Biodiversity Institute.

Stearn WT, 1992. Stearns dictionary of plant names for gardeners: A handbok on the origin and meaning of the botanical names of some cultivated plants. London, UK: Cassell.

Stone CP; Smith CW; Tunison JT (eds), 1992. Alien plant invasions in native ecosystems of Hawai'i: Management and Research. Manoa, Hawaii, USA: Cooperative National Park Resources Studies Unit, University of Hawai'i, 887 pp.

USDA-ARS, 2014. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USDA-NRCS, 2014. The PLANTS Database. Baton Rouge, USA: National Plant Data Center.

Vascular Plants of Antioquia, 2014. Catalogue of the Vascular Plants of the Department of Antioquia (Colombia), Tropicos website. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

Walt JJAvan der, 1977. Pelargoniums of Southern Africa. Cape Town, South Africa: Purnell, 50 pp.

Western Australian Herbarium, 2014. FloraBase - the Western Australian Flora. FloraBase - the Western Australian Flora., Australia: Department of Parks and Wildlife, Western Australia.

Wiersema JH; León B, 1999. World Economic Plants: A Standard Reference. Boca Raton, Florida, USA: CRC Press, 749 pp.

Links to Websites

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Catalogue of Seed Plants of the West Indies
Check list of Myanmar Plants
Checklist of Micronesian Flora
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway source for updated system data added to species habitat list.
Global register of Introduced and Invasive species (GRIIS) source for updated system data added to species habitat list.
USFS Pacific Island Ecosystems at Risk (PIER)


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2/2/2015 Original text by:

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

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA

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