Clerodendrum chinense
(Chinese glory bower)

C. chinense is a highly invasive weed in tropical and subtropical ecosystems. This species has the capacity to move into a habitat and reproduce aggressively by root suckers. C. chinense is classified as a “major weed” in Hawaii, Fiji, Western Samoa, and America Samoa (PIER, 2012) where it grows commonly along roadsides and as an ornamental shrub in gardens. This species rapidly invades pastures and plantations wherever it is planted forming dense thickets that exclude other species (Space and Flynn, 2002; Motooka et al., 2003). In the West Indies, C. chinense is included in lists of invasive species in Cuba, Puerto Rico, and US Virgin Islands (Acevedo-Rodríguez and Strong, 2012; González et al., 2012) and is classified as a widespread exotic plant in the Lesser Antilles (including Antigua, Barbados, Dominica, Grenada, Guadeloupe, Martinique, Montserrat, St. Lucia, and St. Vincent; Broome et al., 2007).

C. chinense is native to southern Asia (probably China and Vietnam). The invasive nature of this species has allowed it to become established in numerous tropical and subtropical areas throughout North America (Florida, Hawaii and Mexico), Central America, South America, West Indies, and the Pacific Islands.

The risk of introduction of C. chinense is high. This species is commonly planted as an ornamental mainly for its foliage and showy flowers, but it produces large amounts of root suckers which can rapidly spread the plant to form dense thickets. The risk of introduction of stems and/or roots as a contaminant of garden soils remains high in those countries where this species is planted. Additionally, C. chinense is still sold in the nursery and landscape trade in many countries and thus it is available for further dispersal. The use of this species for nurseries, gardens, and landscaping should be discouraged and it should be monitored closely for spread.

C. chinense is a rapidly growing shrub that can be found planted in gardens and has the potential to rapidly invade pastures, forest edges, roadsides, and waste grounds. This species prefers to grow in moist environments, full sunlight, with fertile soils, but it can tolerate shade and grow in disturbed areas. In Hawaii, it can be found forming dense canopies in pastures, along streams, and along forest edges, shading out the understory (Motooka et al., 2003). In Fiji, C. chinense is cultivated as an ornamental from near sea level to an elevation of about 900 m, and it is a common element in thickets, coconut plantations, and along roadsides (Smith, 1991).

Genetics

There are no specific genetic studies on this species. However, for many Clerodendrum species, studies available indicate that they are polyploids with a high chromosome number (2n = 46, 48, or 52; Yuan et al., 2010). 

Reproductive Biology

Species in the genus Clerodendrum have an unusual pollination syndrome which avoids self-pollination. The mating system in this genus combines dichogamy and herkogamy. Clerodendrum species have flowers that are protandrous. In these flowers, the stamens and the style are curled upwards tightly inside the flower bud. When the flowers open, the filaments and style start uncoiling. While the filaments project to the centre, the style continues to bend down towards the lower side of the flower. This is the functional male phase. After pollen has been released, the filaments curl back sideways and the style with its receptive stigma (female phase) projects back to the centre, taking the position occupied by the stamens in the male phase (Yuan et al., 2010). 

Physiology and Phenology

C. chinense has been collected in flower throughout the year in the West Indies (Smithsonian US Herbarium). In North America, the flowering phase has been reported from late spring to early summer. 

Longevity

C. chinense is a rapidly growing perennial shrub. 

Environmental Requirements

C. chinense grows in moist environments (annual rainfall greater than 1000 mm) in tropical and sub-tropical climates. This species prefers to grow in areas with full sunlight exposure and fertile soils (pH 5-7). However, C. chinense is also a shade-tolerant and thus it is able to grow in the understory.

Phyllocharis undulata is a species of leaf-eater beetle found in Laos, Cambodia, Vietnam, Peninsular Malaysia, Singapore, Java, Lombok and Timor. This species feeds on various species of Clerodendrum, including C.inerme, C. chinense, and C. calamitosum. It has been considered as a biological control agent against C. chinense (Julien, 1992). Further studies are needed to determine if this beetle species is adequately host-specific and the viability of its application as a biological control agent.

General

• Botanical garden/zoo

Medicinal, pharmaceutical

• Traditional/folklore

Ornamental

• Potted plant
• Propagation material

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.

Physical/Mechanical Control

Mechanical control is difficult: continual slashing will slow spread but not prevent it. Vertical barriers in the soil may prevent further spread if deep enough (PIER, 2012).

Biological Control

The chrysomelid beetle Phyllocharis undulata is a prospective biocontrol agent (Julien, 1992; PIER, 2012). Further studies in this area are needed.

Chemical Control

The use of chemicals to control C. chinense has to be performed very carefully. Herbicides containing triclopyr butoxyethyl ester are suggested as possible herbicides for Western Samoa. Work carried out in Western Samoa has shown that metsulfuron-methyl ester produces effective control. It has been recommended that the plants be cut and the new growth sprayed with herbicide (Waterhouse, 1993). Young plants can be sprayed with a herbicide such as 3,5,6-trichloro-2-pyridinyloxyacetic acid butoxyethyl ester (PIER, 2012). Motooka et al. (2003) suggested that hormone-type herbicides in timely repeat applications will control this weed.

1) Studies on environmental requirements for establishment.

2) Genetic studies to determine variability.

3) Studies assessing the impact of this exotic species on native plants are needed.

4) Recommendations for management and control (biological and chemical control) in invaded areas.

21/09/12 Original text by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

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