Verbesina encelioides
(golden crownbeard)

V. encelioides is a native annual herb in the USA and Mexico, but there exists controversy as to its native status in South America. It has expanded its range into Europe, Asia, Africa and Australia. Cause and timing of initial introductions are mostly unknown. It is considered invasive in the northern Hawaiian Islands due to the displacement of native plant species and the negative impacts it has on breeding colonies of marine birds. It is a dominant invasive on Midway Atoll (PIER, 2013). V. encelioides also invades agricultural crops, especially peanuts, in the United States, Argentina, Australia and India, where allelopathy may provide interference. When grazed upon by livestock (sheep and cattle), animals become lethargic or may die due to the toxin galegine in the plant.

Several sources indicate V. encelioides is native to the southwestern USA, Mexico and South America (Shluker, 1999; Carr, 2012). However, native origins within particular states in the USA, as well as in South America, are questioned (Coleman, 1974). USDA-ARS (2013) includes most of the USA and Mexico in its native range, and USDA-NRCS (2013) includes states as east as Florida and as north as Michigan in its native range. In South America the majority of herbarium collections are from Argentina (GBIF, 2012). See Schluker (1999) for a detailed discussion.

V. encelioides ssp. encelioides has a native range in the eastern and lowland USA (eastern Oklahoma and eastern Texas) and lowland northeastern Mexico, and prefers mesic climates, whereas V. encelioides ssp. exauriculata has a native range in the southwestern USA and into northwestern Mexico, and prefers more arid climates at higher elevations (Coleman, 1966, 1974).

V. encelioides is able to invade various new habitats as the species has evolved in highly diverse ecosystems (Coleman, 1966, 1974). Seed germination in highly variable and in some cases nutrient-poor soil has also enabled the success and naturalization of V. encelioides into new habitats.

V. encelioides is currently cultivated in the Czech Republic (Euro+Med, 2012) and has been transported between Hawaiian islands, most likely on the tyres of vehicles (Shluker, 1999). Although negative environmental impacts have been reported once V. encelioides has naturalized on Hawaiian islands, the species has not been classified as a state noxious weed. Purposeful introductions have not been reported, but this should not be ruled out as the species does produce showy displays of flowers and has been cultivated, both as an ornamental and for its medicinal qualities (Jain et al., 2008).

V. encelioies can be found in a variety of habitats, from riparian to coastal to upland to island. The preferred habitat is tropical to subtropical, with disturbed porous sandy soils and an open canopy (McCoy, 1987). The plant is also found along roads. The species does well on alkaline soils. Habitats with high shade or with very fine soil texture are not optimal sites for this species (Kaul and Mangal, 1987). It may become more invasive on fertile soils; it has been observed to have robust growth when associated with nesting marine birds, and poor growth when on islands with poor soils (Shluker, 1999).

In Hawaii, PIER (2013) reported it as ‘relatively common in dry, disturbed sites, 0-2,805 m’ in altitude.

V. encelioides ssp. encelioides prefers mesic climates, whereas V. encelioides ssp. exauriculata has prefers more arid climates at higher elevations (Coleman, 1966, 1974).

Genetics

n = 17 (Keil and Stuessy, 1977).

Reproductive Biology

Rapid uptake of water leads to germination and rapid plant growth, where flowering and seed production appear limited only by seasonal drought. Larger and heavier seeds have the highest germination rates and are maintained by plants growing in open and sand dune habitats. Although seeds were found to germinate over a wide range of soil moistures (11.3 to 34.8% with >50% germination rate) and temperatures (5 to 20ºC), drought and waterlogged soils suppressed germination. The optimal soil moisture for seed germination was 21% (Kaul and Mangal, 1987). This species is also both self- and cross-pollinated and very fecund, producing ample winged seeds for local dispersal (Kaul and Mangal, 1987).

In its exotic range of northern India, seed germination occurred in February, flowering started in March and the first fruit set started in May, lasting until December. In India V. encelioides emerges after the first cyclonic precipitation and it flourishes in both the hot and humid and cool seasons (Kaul and Mangal, 1987).

Physiology and Phenology

In India, V. encelioides grows well on many soil types and exhibits high phenotypic plasticity and ecological variability (Kaul and Mangal, 1987).

Longevity

V. encelioides is an annual herb.

Environmental Requirements

V. encelioides is considered drought tolerant. It grows best in the 800-900 mm annual rainfall. It is not tolerant to salinity or to shade and requires exposure to light to establish. V. encelioides is adapted to fine or medium textured soil (EPPO, 2013).

The beetle Zygogramma bicolorata was observed attacking V. encelioides in Australia (Withers, 1998, in Anonymous, 2011).

General

• Ritual uses

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

One obvious character found on V. encelioides achenes are wings which can be used for identification (Coleman, 1966, 1974; Baldwin et al., 2012). For a description of the species with images refer to Feenstra and Clements (2008).

This large annual shrub appears from a distance to resemble similar shrub-forming species in Asteraceae, as in the genus Encelia. In contrast to Encelia, V. encelioides has an unpleasant odor and its stems are densely short-hairy with mostly alternate leaves.

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.

V. encelioides has proven most problematic to natural systems when invading oceanic islands (e.g. the Hawaiian islands). Prevention of spread should be focused on between and within-island transportation via vehicle translocation. Cleaning soil from potentially contaminated vehicles or shoes will decrease the likelihood of transport. Purposeful transport for propagation will be by seed.

Infestations are associated with disturbed soils. In these areas management should focus on controlling the spread of known populations with whole-plant removal by manual or chemical means. Eradication should be the goal where feasible, as environmental and sensitive species impacts have been linked to this species.

When found as an agricultural weed, or in pasture, this species should be removed in the same manner as other annual weeds are managed, through physical/mechanical control or chemical control. The rapid germination and robust growth of this species likely precludes the effectiveness of cultural control. Biological control is not currently being explored.

There appears to be a lack of basic and phenologic research conducted on V. encelioides in its native range. This work is needed to assess how it has adjusted to its naturalized range. It appears to be a very plastic species, able to survive and thrive in highly variable systems. The mechanisms and genes that contribute to this adaptive response to novel environments are unknown. The degree of plasticity and rapid evolution responsible for local adaptation is also unknown. Knowledge of these aspects of V. encelioides may aid genetics-based attempts to improve agriculture in arid regions.

22/10/2012 Original text by:

Kai Palenscar, Consultant, USA