Heracleum persicum
(Persian hogweed)

Heracleum persicum is a perennial herb, commonly known as Persian hogweed or golpar, with an anise-like smell. Native to Iran, Iraq and Turkey, it mostly grows in disturbed and semi-natural habitats. Unlike other giant hogweeds, it can propagate vegetatively when sexual reproduction fails. Due to its large size (1.5-3 m in height) and vigorous growth, it can potentially change the vegetation composition of an ecosystem. The plant sap of H. persicum can permanently damage skin if exposed to sunlight. It is considered to be a highly invasive pest, especially since it has colonized Nordic countries within less than 180 years. Introduced to northern Norway via England as an ornamental as early as 1836, it now extensively grows throughout Norway where it is blacklisted under a ‘very high-risk’ category. It is also regulated as quarantine pest in Europe.

H. persicum is native to the Asian countries of Iran, Iraq and Turkey (Fröberg, 2010). It has been introduced widely across Europe, including the Nordic countries of Northern Europe (Denmark, Finland, Iceland, Norway and Sweden) where it is invasive (Jahodová et al., 2007; Fröberg, 2010). It has also been reported from UK, Czech Republic, Estonia, and Hungary (Nielsen et al., 2005; Jahodová et al., 2007; DAISIE, 2015; EPPO, 2015; NOBANIS, 2015).

H. persicum was deliberately introduced as an ornamental plant, but this is less likely to happen now that its negative effects are widely known.

Transportation and hydrochory may still spread H. persicum into new locations since H. persicum predominantly grows along roadsides and seashores. Cross-border public and private transport is common in Europe and particularly frequent in Scandinavia resulting in a high probability of accidental introduction.

H. persicum has been recommended for regulation as a quarantine pest in Europe (EPPO, 2015). 

H. persicum generally occupies the same habitats as H. mantegazzium. These are disturbed and semi-natural habitats, such as roadsides and railroads, as well as meadows, grasslands, disused agricultural land, ruderal areas, coastal beaches and along streams and rivers. It can be found in most of the open areas around cities in Norway and Finland, in gardens and parks (EPPO, 2009; Klingenstein, 2006). H. persicum is shade intolerant in general, however recent expansion in semi-natural habitats indicates its adaptation under tree canopy. It is becoming increasingly found along forest edges in Norway and has been reported as growing in birch forest (Fremstad and Elven, 2006). H. persicum predominantly occupy roadsides and seashores at least in Denmark, Norway and Sweden. The details regarding variation in habitat among countries are lacking.

Genetics

The chromosome number of H. persicum is 2n=22 and n=11(IPCN Chromosome Reports, 2015). Fröberg (2010) noticed deviating morphotypes of H. persicum from Finland and Sweden. He observed densely hairy lower leaf surfaces; similar to H. mantegazzianum, the rays and pedicels lack hairs and have papillae; and the ovaries/fruits have shorter hairs than H. persicum. Among introduced populations, Danish and Norwegian populations are quite distinct from each other whereas English, Finnish, Latvian and Swedish populations share genotypes with Danish and Norwegian populations (Jahodová et al., 2007). H. persicum generally hybridizes with H. sphondylium in northern Norway (Rijal et al., 2014). It has also been reported to hybridize with H. mantegazzianum (Fröberg, 2010).

Reproductive Biology

H. persicum is polycarpic. Unlike other invasive giant hogweeds, it repeatedly flowers and can survive via vegetative reproduction even if sexual reproduction fails. In northern Norway, the plant starts growing when snow is melted, i.e., approximately at the end of March. Average flowering age of the plant has not been quantified yet but may be approximately similar to H. mantegazzianum, i.e. 2-5 years (Perglová et al., 2007).

H. persicum is possibly protandrous since protandry is common in the Apiaceae family and it has been reported for H. mantegazzianum (Perglová et al. 2006; Perglová et al. 2007), a species often confused with H. persicum. The temporal variation in flower maturation is visible between primary and secondary umbels of H. persicum (DP Rijal, The Arctic University of Norway, unpublished data). It may be self-compatible but cross-pollination appears equally likely if H. persicum is protandrous.

Only primary umbels produce fertile seeds whereas secondary and tertiary umbels act as pollen donor and are abortive (Often and Graff, 1994). Seed production depends on the size of the inflorescence. Each plant has 40-50 umbellules and 20-40 fruits per umbellule. Each fruit is composed of two mericarps (seeds) and, based on a conservative estimation a single plant can produce, 1600-4000 seeds (DP Rijal, The Arctic University of Norway, personal observation, 2015). Some seeds collected in early November 2012 were used in a seed germination experiment; seed germination rate was 2.1 % for the northern Norwegian population (DP Rijal, The Arctic University of Norway, unpublished data). A higher rate of seed germination is expected if seed collection is done right after the seeds are mature, i.e., mid to late September. Seed reproduction also varies in H. persicum, for example, it is less common in southern than in northern Norway (DP Rijal, The Arctic University of Norway, personal observation, 2015). In any case, seed reproduction is not as vigorous as H. mantegazzianum (Fröberg, 2010).

Physiology and Phenology

Clonality in H. persicum seems an adaptive feature to survive the extreme weather of northern Norway. Such a feature is absent in other giant hogweeds. As a consequence, other giant hogweeds could not grow in most of the places where H. persicum is growing. Seeds of H. persicum remain dormant for a longer period in its native than introduced range (M Falahati-Anbaran, University of Guilan, Iran, personal communication, 2015). Salehani et al. (2013) found a lower germination rate and slower germination speed on seeds originating from higher than lower elevations in native range and found no germination if seeds are not stratified. The extensive growth of H. persicum in northern Norway might be benefitted by shorter seed dormancy as germination does not require stratification. Otherwise, H. persicum would not survive in higher latitudes with shorter growing season.

H. persicum flowers earlier in its southern range (warmer areas) than in its northern range (colder areas), from early/mid-July to late August on average (Often and Graff, 1994; Nielsen et al. 2005).

Environmental Requirements

Clonality in H. persicum seems an adaptive feature to survive the extreme weather of northern Norway. Such a feature is absent in other giant hogweeds. As a consequence, other giant hogweeds could not grow in most of the places where H. persicum is growing. Seeds of H. persicum remain dormant for a longer period in its native than introduced range (M Falahati-Anbaran, University of Guilan, Iran, personal communication, 2015). Salehani et al. (2013) found a lower germination rate and slower germination speed on seeds originating from higher than lower elevations in native range and found no germination if seeds are not stratified. The extensive growth of H. persicum in northern Norway might be benefitted by shorter seed dormancy as germination does not require stratification. Otherwise, H. persicum would not survive in higher latitudes with shorter growing season.

H. persicum flowers earlier in its southern range (warmer areas) than in its northern range (colder areas), from early/mid-July to late August on average (Often and Graff, 1994; Nielsen et al. 2005).

A new nematode of order Tylinchida and family Heteroderidae, Heterodera persica, has been reported to parasitize on H. persicum in its native range (Maafi et al., 2006). However, it has not been used yet to control H. persicum.

Environmental

• Amenity

General

• Botanical garden/zoo

Human food and beverage

• Spices and culinary herbs

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Look for the diagnostic characters of the species: plant height generally 1.5-3 m, convex umbel, multiple stems, stem continuously purplish at base, plant smells like anise. Other details of identifying characters are provided elsewhere (Often and Graff, 1994; Nielsen et al., 2005; EPPO, 2009; Fröberg, 2010).

Seeds of the species can be smashed and in order to release the anise smell.

H. persicum is often confused with H. mantegazzianum and H. sosnowskyi. The two latter species are generally taller (more than 3 m), have only a single stem, branched inflorescence up to tertiary level and an umbel which is mostly flat. Leaves and seeds of H. persicum impart a strong anise-like smell that is not present in other species. Stem is generally 1-5, basal part of the stem is purplish, and inflorescence is convex in H. persicum (Nielsen et al., 2005; Fröberg, 2010).

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

Rapid response

Both regional and local cooperation are required to combat H. persicum since it can easily cross political borders. Fortunately, all of the Nordic countries (where H. persicum occurs) are connected to one or more scientific networks, such as EPPO and NOBANIS, which are actively involved in invasive species management at a European scale.

Eradication

Complete eradication of H. persicum appears unlikely as it has invaded a fairly wide area in its introduced range, i.e., from 51.5 to 71.0°N (Rijal et al., 2015). However, effective prevention and control measures, in the end, should help eradicate species.

Control

Physical/mechanical control

Root cutting (digging), mowing, inflorescence removal and entire plant removal has been recommended as suitable methods for controlling H. mantegazzianum (Nielsen et al., 2005). Mowing of H. persicum 2-3 times during a growing season has not been very effective in northern Norway. Instead, density of plants is increasing each year and some plants are flowering even after mowing a couple of times in a season (DP Rijal, The Arctic University of Norway, personal observation, 2015).

Unlike other giant hogweeds, H. persicum is truly perennial and can reproduce vegetatively when sexual reproduction fails. Thus, inflorescence or plant cutting would not be completely effective. However, mechanical or physical methods that efficiently uproot the plant should help control species.

Biological control

Biological control of H. persicum has not been attempted before. However, a recently discovered parasitic nematode, Heterodera persica (Maafi et al., 2006), may be utilized as a biological control in H. persicum’s introduced range. In the meantime, it is important to emphasize that H. persicum has attained a significantly different genetic architecture in its introduced range than in its native range (Jahodová et al., 2007). This may demand more than one biological control agents to parasitize on different genotypes in the introduced range.

Chemical control

Chemical treatment is considered as one of the effective and cheapest methods, and H. mantegazzianum has been reported to be susceptible to glyphosate and triclopyr (Nielsen et al., 2005). Glyphosate is a general herbicide that can effectively kill any plant species. Thus, H. persicum should also be susceptible to glyphosate. Unlike H. mantegazzianum, H. persicum spreads by vegetative growth. If glyphosate kills an aerial part but not the entire plant, then it may be less effective on H. persicum. Nielsen et al. (2005) suggested the use of more than one method to effectively combat giant hogweeds. Excessive use of chemical should be discouraged as it contaminates neighbouring water body as well as kills resident vegetation. 

Salt is often used by residents in Norway to try and kill H. persicum (Alm, 2013).

Control by utilization

Utilization of H. persicum has not been realized yet in its introduced range. H. persicum is being used in traditional medicine and for culinary purposes in its native range. Chemical screening of individuals from its native range has ranked H. persicum as a potential plant for commercial medicines.

Ecosystem Restoration

Case studies of the restoration of H. persicum invaded areas is lacking, however the general procedure of restoration should be similar to that of H. mantegazzianum. The nutrient-rich and denuded area, after eradication, is more sensitive to erosion and susceptible to novel invasion. In such case, re-vegetation or grassland management would be the best response (Nielsen et al., 2005). The habitat could be restored by sowing a mixture of native grasses that: have been proven to be competitive; produce dense swards; can grow in mixtures; are vigorous after repeated cutting (Nielsen et al., 2005). Such practices do not allow invasive species to re-establish.

Ecological requirements of H. persicum (e.g. range of soil pH, moisture requirement, temperature tolerance) have not received ample consideration. Reproductive biology, physiology and phenology, environmental requirement and biological interactions also require further research.

31/03/2015 Original text by:

Dilli Prasad Rijal, The Arctic University of Norway, Norway