Stachytarpheta cayennensis
(blue snakeweed)

Pictures

Picture	Title	Caption	Copyright
Title Flowers Caption Stachytarpheta cayennensis (blue snakeweed); flowers. West Kuiaha Rd, Haiku, Maui, Hawaii, USA. November, 2006. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Flowers	Stachytarpheta cayennensis (blue snakeweed); flowers. West Kuiaha Rd, Haiku, Maui, Hawaii, USA. November, 2006.	©Forest Starr & Kim Starr - CC BY 4.0
Title Invasive habit Caption Stachytarpheta cayennensis (blue snakeweed); flowering habit - all the darker areas are Stachytarpheta. East Poelua West Maui, Maui, Hawaii, USA. May, 2009. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Invasive habit	Stachytarpheta cayennensis (blue snakeweed); flowering habit - all the darker areas are Stachytarpheta. East Poelua West Maui, Maui, Hawaii, USA. May, 2009.	©Forest Starr & Kim Starr - CC BY 4.0
Title Habit Caption Stachytarpheta cayennensis (blue snakeweed); habit. Kilauea Pt NWR, Kauai, Hawaii, USA. March, 2013. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Habit	Stachytarpheta cayennensis (blue snakeweed); habit. Kilauea Pt NWR, Kauai, Hawaii, USA. March, 2013.	©Forest Starr & Kim Starr - CC BY 4.0
Title Leaves Caption Stachytarpheta cayennensis (blue snakeweed); leaves. Kipahulu LZ Haleakala National Park, Maui, Hawaii, USA. February, 2009. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Leaves	Stachytarpheta cayennensis (blue snakeweed); leaves. Kipahulu LZ Haleakala National Park, Maui, Hawaii, USA. February, 2009.	©Forest Starr & Kim Starr - CC BY 4.0
Title Habit Caption Stachytarpheta cayennensis (blue snakeweed); general habit. Note the long, 'snaking', inflorescenses. Loxahatchee National Wildlife Refuge, Florida, USA. September, 2009. Copyright ©Forest Starr & Kim Starr - CC BY 4.0	Habit	Stachytarpheta cayennensis (blue snakeweed); general habit. Note the long, 'snaking', inflorescenses. Loxahatchee National Wildlife Refuge, Florida, USA. September, 2009.	©Forest Starr & Kim Starr - CC BY 4.0

Identity

Preferred Scientific Name

• Stachytarpheta cayennensis (Rich.) Vahl

Preferred Common Name

• blue snakeweed

Other Scientific Names

• Stachytarpheta australis Moldenke
• Stachytarpheta dichotoma (Ruiz Lopez & Pavon) Vahl
• Stachytarpheta urticaefolia (Salisb.) Sims
• Valerianoides cayennensis (Rich.) Kuntze
• Verbena cayennensis Rich.

International Common Names

• English: blue porterweed; blue rat's tail; bluetop; branched porterweed; brazilian tea; cayenne porterweed; cayenne snakeweed; false verbena; joee; nettleleaf porterweed; nettleleaf velvetberry; nettleleaf vervain; rattail; rough leaved false vervain
• French: herbe à chenille; herbe bleue; queue de rat

Local Common Names

• : piche de gato; rabo de zorro
• Brazil: gervâo; gervao-urticante
• Cook Islands: tiaki
• Fiji: finak ne puak; lavenia; se karakarawa; serakawa; tumbutumbu; turulakaka
• French Polynesia: piripiri
• Japan: honagaso
• Kiribati: te uti
• Micronesia, Federated states of: ouchung; sakura
• Nauru: edidubai; edidubaiy
• Niue: mautofu samoa; motofu
• Palau: louch beluu
• Samoa: fua pepe; fua pepe; mautofu; mautofu tala; mautofu vao; taioti; vao pepe
• Tonga: ‘i kuma; ‘iku ‘i kuma; hiku ‘i kuma
• USA/Hawaii: oi; owi

EPPO code

• STCHI (Stachytarpheta cayennensis)

Summary of Invasiveness

S. cayennensis is a shrub native to South and Central America and the Caribbean. It was introduced widely introduced into several tropical countries around the world as an ornamental species due to its attractive blue flowers, but in some countries it has become invasive. S. cayennensis has a wide environmental tolerance and often invades disturbed areas where it can outcompete native flora. It is invasive in many Pacific islands and is regarded as a noxious weed in the Northern Territory, Australia and is increasing in abundance in Florida, USA. According to a risk assessment this species is regarded as being highly invasive (score 20 = high risk) (PIER, 2015).

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Lamiales
•                         Family: Verbenaceae
•                             Genus: Stachytarpheta
•                                 Species: Stachytarpheta cayennensis

Notes on Taxonomy and Nomenclature

S. cayennensis belongs to the Verbenaceae family which comprises around 100 genera. The genus Stachytarpheta has undergone a series of taxonomic revisions that are further complicated by putative hybrids (Wilson et al., 2009). A total of 32 synonyms of S. cayennensis, including varieties, have been reported (The Plant List, 2013). Further details of the taxonomic history can be found in Munir (1992).

A number of species within the genus Stachytarpheta are also known to be invasive weeds.

Stachy(s) (a spike, originally an ear of corn) describes the elongate inflorescence, and tarphy (thick) refers to the thickened or densely flowered flower stalks. The plant was named after the capital of French Guiana, Cayenne.

The genus Stachytarpheta contains about 65 species, mostly from the American tropics. Many of which are regarded as being weedy throughout the tropics and subtropics. The closely related species S. jamaicensis is similar in appearance to S. cayennensis and the common names for these species are often used interchangeably.

Description

S. cayennensis is a perennial evergreen herb or subshrub which can reach heights of 2.5 m. It has a woody glabrous stem with several branches. Leaves opposite, membranous, elliptic to broadly elliptic or ovate, 4-8 cm long, 2-4.5 cm wide, upper surface rugose, both surfaces glabrous or occasionally lower surface with a few scattered hairs usually along the veins and margins, margins sharply and coarsely serrate, the teeth conspicuously divergent, apex acute, base cuneate, petioles 0.5-2 cm long. Spikes slender, rachis flexuous to erect or somewhat nodding, 14-40 cm long, ca. 2.5 mm in diameter, the furrows somewhat shallow, nearly as wide as the rachis, bracts lanceolate, ca. 7 mm long; calyx ca. 7 mm long, the teeth subequal; corolla usually dark purplish blue with a paler center, the tube 7-8 mm long (Wagner et al., 1999).

Distribution

The native range of S. cayennensis includes much of the Americas, from Mexico, Central America and the Caribbean, through tropical South America to southern Brazil (Weeds of Australia, 2011).

This species has been introduced into all of the continents with tropical and subtropical climates between 30° N and 30° S parallels.

Distribution Table

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.

History of Introduction and Spread

The majority of introductions throughout the world are as a result of intentional introductions for ornamental purposes. S. cayennensis produces an attractive blue flower which is appealing to bees and butterflies.

In 1868 S. cayennensis was introduced into New Caledonia as fooder for livestock (Blanfort et al., 2008).

Risk of Introduction

The risk of S. cayennensis being introduced into new areas is fairly high as seeds of this species are readily available for sale on the internet. In addition to this, it can disperse locally by winds, attachment of seeds to vehicles and animals or as a contaminant in hay (Weeds of Australia, 2011). A risk assessment conducted by PIER (2015) gave this species a high score of 20 and therefore would reject its import due to its invasive tendencies.

Habitat

S. cayennensis is common in open field like pastures, crop fields, moorlands, fallow lands, roadsides and wastelands. This species is also tolerant to shade and may invade low density forests. S. cayennensis grows on every type of soils, including infertile and dry soils. Although it can tolerate drought, this species grows best in moist, deep, fertile soils in disturbed areas (HEAR, 2012).

Habitat List

Hosts/Species Affected

S. cayennensis may outcompete smaller native plant species and crops dedicated to livestock are often affected by smothering. In Australia, this species is commonly found as a weed of pastures and sugarcane (Saccharum species) (DAFF, 2014).

Climate

Latitude/Altitude Ranges

Means of Movement and Dispersal

Natural Dispersal

Seeds of S. cayennensis may be dispersed over short distances by rain and run-off. There is some indications that this species may reproduce and spread locally by vegetative propagation (PIER, 2015).

Vector Transmission

Seeds of this species may become attached to the fur of animals and translocated over short distances into new areas (Weeds of Australia, 2011).

Accidental Introduction

It is believed that the spread of this species in Queensland, Australia is a result of accidental introductions via fodder, hay and contaminated pasture seed (Smith, 2002). Seeds may also be introduced into new areas in garden waste or by attachment of seeds to clothing, vehicles and machinery (Weeds of Australia, 2011).

Intentional Introduction

S. cayennensis was intentionally introduced into a number of countries as an ornamental species. This species produced an attractive blue flower which is appealing to bees and butterflies. Seeds of this species are still readily available for sale on the internet.

Impact Summary

Environmental Impact

Impact on Habitats

S. cayennensis is unpalatable to livestock and in areas with heavy grazing this species may outcompete surrounding species (HEAR, 2013).

Impact on Biodiversity

This species is opportunistic and can readily invade disturbed areas. It can form dense thickets which may outcompete or smother native plant species (PIER, 2015). In Florida this species is regarded as a Category II plant, a species which has increased in abundance but has not yet altered plant communities (FLEPPC, 2009).

Risk and Impact Factors

• Proved invasive outside its native range
• Highly adaptable to different environments
• Pioneering in disturbed areas
• Tolerant of shade

• Reduced native biodiversity

• Competition - monopolizing resources
• Competition - shading
• Hybridization

• Highly likely to be transported internationally deliberately
• Difficult to identify/detect in the field

Uses

Economic Value

There is no information available on the economic value of S. cayennensis. As an ornamental this species is sold in the nurseries and via the internet and therefore has some economic value.

Social Benefit

In Latin America, S. cayennensis is utilised in traditional medicine to treat symptoms of malaria, treat dysentery and liver disorders, to relieve fevers and to act as a sedative (Taylor, 2012). The plant contains flavonoids, terpenes, phenols and steroids and has been found to have anti-inflammatory and anti-malarial properties (Okoye et al., 2014).

Similarities to Other Species/Conditions

Others species within the genus Stachytarpheta closely resemble S. cayennensis. These include S. jamaicensis, S. australis and S. mutabilis. The colour of the flower is often used to differentiate between the species. The flowers of S. jamaicensis are light blue or mauve, S. australis has light blue or white flowers and the stem and lower face of leaves are pubescent and S. mutabilis is characterized by having larger pink or red flowers with a hairy stem.

Hybridization between the closely related species S. cayennensis and S. jamaicensis may occur. The hybrids more closely resemble S. jamaicensis, but the corollas are darker in colour than typical in S. jamaicensis. The habit is more erect, and the leaves are usually more ovate, darker green and with more divergent teeth similar to S. cayennensis (Wagner et al., 1999). S. cayennensis may also hybridize with S. mutabilis. A number of hybrids have been found to have naturalized in Queensland (Weeds of Australia, 2011).

S. cayennensis is also similar in appearance to Verbena litoralis and V. officinalis however these have four stamens instead of two with smaller flowers which are less than 4 mm across (Weeds of Australia, 2011).

Prevention and Control

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.

Prevention

SPS Measures

In Australia, S. cayennensis is regarded as an environmental weed and regulations are in place in a number of territories to prevent its spread. In New South Wales this species is restricted, meaning that it cannot be sold or distributed within the territory. In the Northern Territroy this species has been declared a noxious weed. This means that the spread of this species must be controlled and that introductions are prohibited (Weeds of Australia, 2012).

S.cayennensis is included in a list of the 33 most invasive species of the South Pacific (Blanfort et al., 2008).

Control

Physical/Mechanical Control

Manual removal of seedlings by hand can be effective for small populations, ensuring the large roots are also removed. S. cayennensis may also be controlled by chipping or cultivation (ploughing, grubbing and hoeing) (Swarbrick, 1997). Planting of local and vigorous pasture plants, such as legumes, may compete with S. cayennensis and prevent re-establishment.

Biological Control

No biological control agents have been released for S. cayennensis, however possible agents are discussed by Waterhouse and Norris (1987). The potential for biological control of the closely related species S. jamaicensis is discussed in detail by Cock et al. (1985).

Chemical Control

It has been suggested that S. cayennensis is sensitive to foliar application of 2,4-D or MCPA (Motooka et al., 2003). It is however, less sensitive to other hormone type herbicides, although drizzle application of triclopyr in water have been found to be effective in trials in Palau (Motooka et al., 2003). Some control using glyphosate has been recorded. The best control of S. cayennensis can be achieved during the summer months when plants are actively growing (Weeds of Australia, 2011).

IPM

For large areas of S. cayennensis it is recommended that plants are mechanically removed and treated with herbicides. The best time to cut plants is before flowering. It is necessary to follow up and retreat areas with herbicides to provide effective control (Weeds of Australia, 2011).

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Principal Source

Draft datasheet under review

Contributors

31/03/2015 Original text by:

Erwan Le Nezet, Service d'Etat de l'Agriculture, de la Forêt et de la Pêch, Wallis and Futuna

Distribution Maps