Stachytarpheta urticifolia
(rattail)

Identity

Preferred Scientific Name

• Stachytarpheta urticifolia (Salisb.) Sims

Preferred Common Name

• rattail

Other Scientific Names

• Cymburus urticaefolius Salisb., nom. illegit.
• Zappania urticifolia (Sims) Poir.

International Common Names

• English: blue rat’s tail

Local Common Names

• Bangladesh: nilkanthi
• Fiji: finak ne puak; sere
• India: tharoi-phijup
• Tokelau: mautofu
• Tonga: hiku 'i kuma

Summary of Invasiveness

S. urticifolia is a perennial semi-woody herb. It has been grown in gardens for over 200 years. It is a popular ornamental and has been planted in gardens globally because of its attractive blue flowers. It has a very high reproductive rate and in tropical climates the species escapes from cultivation readily. It can form monocultures, invade moist deciduous forests, and interrupt successional processes. It has allelopathic properties that give it the ability to compete with other plant species. The species is highly likely to be transported intentionally to new regions and escape.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

Stachytarpheta is a genus of about 133 species in the Verbenaceae, distributed mainly in tropical America (Atkins, 2005). Stachytarpheta urticifolia was described by John Sims in 1816 from plants cultivated in London by John Walker (Sims, 1816). The original provenance of Walker’s plants were unknown. The validity of this species has been controversial, complicated by the lack of a type specimen (Munir, 1992; Chen and Wu, 2003). As the type specimen cannot be found the species was lectotypified by Daniel and Rajendran (1992), designating the illustration in the original publication by Sims.

Some recent authors include S. urticifolia in synonymy of Stachytarpheta cayennensis, a native of tropical America (Munir, 1992; Wunderlin and Hansen, 2003). However, other authors recognize the species as distinct (Nicolson, 1991; Verdcourt, 1992; Chen and Wu, 2003; Devi, and Singh, 2005; Acevedo-Rodriguez and Strong, 2016). As discussed by Chandler et al. (2014), the taxonomy needs additional study. This problem is unlikely to be resolved until a comprehensive study is conducted of this and similar species.

Complicating matters further, the identification of S. cayennensis, Stachytarpheta indica, and Stachytarphetajamaicensis species has been problematic on a global scale. Confusion and misidentification of these species in the literature is rampant. For example, Chen and Wu (2003) found that in Taiwan nearly all reports of S. jamaicensis represented S. urticifolia and considered the name S. cayennensis to be misapplied to S. jamaicensis. In India Rajendran and Daniel (1992) found the name S. indica to be misapplied to both S. urticifolia and S. jamaicensis.

For the purposes of this datasheet S. urticifolia is treated as a valid species,  following Verdcourt (1992), Chen and Wu (2003), and Devi and Singh (2005). Most distributional data presented here is tentative. Unravelling literature reports and clarifying global ranges of S. urticifolia, S. cayennenis, S. jamaicensis, and S. indica will be impossible until species concepts are resolved, and specimens then examined through the ranges of each taxon.

Some authors have used the spelling S. urticaefolia rather than S. urticifolia, and have also attributed the authorship to Salisbury (e.g. as S.urticaefolia (Salisbury) Sims). Sims (1816) clearly spells his new epithet as “urticifolia”, but refers to an earlier name by Salisbury: Cymburus urticaefolius. As has been discussed by Nicolson (1991) and Verdcourt (1992), the Salisbury name is illegitimate and excluded from synonymy by Sims. Thus, the proper spelling and authorship of the species is S. urticifolia Sims. 

Description

The following is adapted from Chen and Wu (2003).

Perennial semi-woody herb; weakly erect, 80-200 cm tall, the stem or branches dichotomous, 4-angled, dark green flushed with purple. Leaves opposite, membranous; blade ovate to broadly elliptic, 5-8 cm long, 3-6 cm wide, bullate above, obtuse or abruptly acute apically, coarsely serrate with sharp outward-pointing teeth, cuneately narrowed basally, petiole 0.5-2 cm long. Spikes terminal, flexible during anthesis, 25-40 cm long, 3 mm in diameter. Flowers sessile, 3-5 flowers open at a time; calyx tubular, compressed, 5-6 mm long; corolla salverform, dark purple-blue, with a white eye at the base of upper lip, 8-9 mm long, perfect stamens 2, filament 1.2 mm long and 0.3 mm wide, anthers light yellow; stamens included; style elongated, exerted, 7 mm long, white flushed with purple. Fruit enclosed by the persistent calyx, black, oblong and compressed, 4 mm long and 1.5 mm wide; seed closely enclosed by the thin pericarp.

Distribution

The original distribution of S. urticifolia is ambiguous. The description by (Sims, 1816) was based on cultivated plants in England and does not indicate provenance. Verdcourt (1992) treated the species as a native of tropical Asia and the Pacific. Nicolson (1991) considered it as a native to Asia and as introduced in the Caribbean. Chen and Wu (2003) also consider it as probably native to tropical Asia. The historic range in Asia is unknown. 

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

S. urticifolia was in cultivation as early as the early 1800s in London, UK (Sims, 1816). Its early use as a garden plant had led to an obscure native range, and to the global spread of the species. It was introduced to Taiwan by 1925 as an ornamental (Chen and Wu, 2003), for example. It was first found in India between 2001 and 2004 (Devi and Singh, 2005). The dates of introduction to many parts of its range are unknown, in part, due to confusion in the literature between this and related species, a problem that will not be unraveled until these species receive a global taxonomic revision.

Introductions

Risk of Introduction

S. urticifolia is a widely used ornamental plant, cultivated for its attractive flowers. Seed is sold on the Internet. It is highly likely to be introduced to new regions through the landscape trade, and to escape from cultivation in regions with favourable tropical climates.

Habitat

S. urticifolia is primarily a weed of disturbed areas, but can invade natural habitats. It is an aggressive colonizer of disturbed areas (Reddy et al., 2008). The species is mostly shade intolerant (Kuo, 2003), but can colonize in deciduous forests (Reddy et al., 2008; Sunilkumar, 2015). In Africa, Verdcourt (1992) records it for grassland, bushland, and forests to an elevation of 1200 m. In Taiwan it has also been found on beaches, as well as disturbed areas and secondary woodland (Chen and Wu, 2003).

Habitat List

Biology and Ecology

ReproductiveBiology

Kuo (2003) conducted a study of the reproductive biology of S. urticifolia. Plants were able to flower for most of the year. Reproductive output was very high with a single plant having the ability to produce 7000 seeds/year. The species is adapted best to high light environments, with the highest seed germination under light conditions. The species can sometimes reproduce asexually by rooting at stem nodes. Ekanayakc et al., (2007), in a study of Sri Lankan species including S. urticifolia, report that Stachytarpheta species, found that flowers are bisexual and functional for only 12-14 hours. They are usually insect pollinated, especially by bees and butterflies. S. urticifolia was found to be both self- and cross-compatible. Seeds germinated within 11-14 days.

Physiology and Phenology

S. urticifolia is a perennial. Kuo (2003) also found that S. urticifolia in Taiwan is allelopathic. Aqueous leaf extracts inhibited germination and growth of several herbaceous species and decaying leaves caused high mortality of several herbaceous species. The species is mostly shade intolerant (Kuo, 2003), but can colonize in deciduous forests (Reddy et al., 2008; Sunilkumar, 2015).

Climate

Natural enemies

Notes on Natural Enemies

The sap-sucking insect Aleurodicus dispersus (spiral whitefly), has been documented on S. urticifolius in the Seychelles (Hazell et al., 2008).     

Means of Movement and Dispersal

Vector Transmission

While no reports have assessed any specific seed dispersal mechanisms of S. urticifolia, the very similar Stachytarpheta cayennensis is reported in Australia to be spread by attaching to animal fur and to machinery (Weeds of Australia, 2011).  

Accidental Introduction

S. cayennensis has also been documented as being dispersed through the dumping of landscape material and in contaminated soil so this may also be the case for S. urticifolia (Weeds of Australia, 2011).  

Intentional Introduction

S. urticifolia has spread outside of its native range through its use as an ornamental. It was cultivated in England by the early 1800s (Sims, 1816).

Impact Summary

Environmental Impact

Impact on Habitats

S. urticifolia is a weed of disturbed areas, moist deciduous forests, beaches, brushland and grassland. It has the ability to compete with native species where it becomes established. For example, in the Ogasawara Islands, Japan, it invades disturbed areas and prevents the regeneration of native species by disrupting successional processes (Abe et al., 2014).

Impact on Biodiversity

S. urticifolia has allelopathic properties (Kuo, 2003). When the species escapes it can effectively outcompete desirable native species. S. urticifolia may impact rare and endangered species, but this has not been accurately evaluated. In Hawaii it has been listed as impacting the subshrub Schiedea spergulina var. leiopoda (USFWS, 2010). However, while S. urticifolia has been reported for Hawaii (Wagner et al., 1999), more recently the populations of Stachytarpheta formerly called S. urticifolia in the Hawaiian archipelago have been considered to represent S. cayennensis (Wagner and Herbst, 2003). 

Risk and Impact Factors

• Invasive in its native range
• Proved invasive outside its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential
• Reproduces asexually

• Ecosystem change/ habitat alteration
• Reduced native biodiversity
• Threat to/ loss of native species

• Allelopathic
• Competition - monopolizing resources

• Highly likely to be transported internationally deliberately
• Difficult to identify/detect as a commodity contaminant

Uses

Economic Value

The primary economic value of S. urticifolia is as an ornamental species. Due to its attractive blue flowers, which attract a diversity of pollinators, it is grown in tropical regions. Plants are sold in nurseries and seeds are sold on the Internet.

Social Benefit

Stachytarpheta species are often used as traditional medicines. In Bangladesh S. urticifolia has been used as a anthelmintic, abortifacient and used traditionally in venereal diseases, ulcers, dropsy, fevers, stomach troubles and rheumatic inflammations. An infusion of bark is used in treating diarrhea and dysentery (Chowdhury et al., 2004).

Similarities to Other Species/Conditions

S. urticifolia is similar to Stachytarpheta cayennensis, Stachytarpheta jamaicensis and Stachytarphetaindica and the three species have been widely confused. Verdcourt (1992) includes a key to all four species and Chandler et al. (2014) provides a table summarizing their differences. Devi and Singh (2005) and Sunilkumar (2015) include keys to three species (excluding S. indica). S. jamaicensis differs in habit, being a decumbent to ascending shrub, having oblong to ovate-elliptic leaves, and an only indistinctly bullate adaxial leaf surface. S. cayennensis (= Verbena cayennensis, S. dichotoma) has thinner fruiting spikes (ca 2.5 mm diameter) with little swelling over the fruits; flowers small and pale in colour, varying from mid to pale blue to almost white, the tube 4 to 5 mm long and limbs only 4 to 6 mm long. S. indica (= S. bogorensis, Verbena indica), has soft leaves with the lower margins of the middle leaf teeth at least twice as long as the upper margins. This species occurs sporadically from Central America, through Africa and Asia to Australia. Further species of Stachytarpheta are occasionally found as weeds in the tropics and subtropics, including Stachytarpheta angustifolia, Stachytarpheta australis and Stachytarpheta mutabilis.

Rajendran and Daniel (1992) reports herbarium specimens collected in India that may be hybrids between S. urticifolia, S. jamaicensis, and S. mutabilis.

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

S. urticifolia usually becomes established after escaping from cultivation. Eliminating the use of the species as a garden plant would help to prevent escape to new areas.

Control

Control of the species can be achieved with either physical or chemical control, depending on population size. Long-term management of disturbed habitats prone to invasion by the species requires management of successional processes to make conditions unfavourable to occupation by S. urticifolia, including reintroduction of native hardwood species.

Physical/Mechanical Control

Individual plants of S. urticifolia can be easily hand-pulled.

Chemical Control

A variety of herbicides are effective for the control of Stachytarpheta species. Motooka et al. (2002) recommends foliar application of 2,4-D or MCPA. Glyphosate can also be used effectively (Weeds of Australia, 2011).

Gaps in Knowledge/Research Needs

The weedy species of Stachytarpheta which include S. urticifolia, Stachytarpheta cayennensis, Stachytarpheta indica and Stachytarpheta jamaicensis are in need of taxonomic revision (Chandler et al., 2014).

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Contributors

23/06/16 Original text by:

Keith Bradley, Consultant, South Carolina, USA

Distribution Maps