Pyracantha coccinea
(scarlet firethorn)

Pyracantha coccinea is a thorny shrub, native to southern Europe and western Asia, which has been widely introduced, primarily as an ornamental plant. It is of some concern due to its potential effects on natural habitats and its being a potential reservoir of the fruit-tree pathogen Erwinia amylovora, but is has only been recorded as invasive in a small number of countries, and in most of these sources differ as to how invasive it is.

Pyracantha coccinea is native from southern Europe into the Caucasus Mountains in western Asia (Floridata, 2017). There are fossil records from the Pleistocene of the species extending into the north of Italy and into the UK, indicating that the temperature ranges were considerably warmer than at present (West et al., 1960; Sparks and West, 1970, Martinetto 2009). The species has been widely introduced and  is reported as present in Asia, Africa, North America, Central America, the Caribbean, South America, Europe and Oceania (see Distribution Table for details).

Pyracantha coccinea has been reported as invasive in Cuba, USA, Argentina and Japan, but not all sources agree on this. Vergara-Tabares et al. (2016) cite the species as being invasive at Japan, but it is not on the list of invasive species for that country, only reported as an alien species (National Institute for Environmental Studies, 2017). Oviedo Prieto et al. (2012) list it as invasive in Cuba, but no details are provided, the genus is not suited to hot tropical areas (Csurhes et al., 2016), and the species is not reported as present elsewhere in the West Indies by Acevedo-Rodríguez and Strong (2012).

In the USA the species is reported as invasive for Texas (Texas Invasives, 2017), but according to Nesom (2009) it is not invasive there as it falls under category F3 (“a species known from relatively few numbers, known from relatively few localities, usually in disturbed habitats, repeatedly introduced or perhaps merely long-persisting at some localities, not showing aggressively invasive tendencies, or perhaps incipiently invasive”). Although listed as invasive for Georgia in the Invasive Plant Atlas (Swearingen and Bargeron, 2017), it is listed there as a Category 4 exotic plant, defined “as being naturalized, but generally not posing a problem in natural areas or as a potentially invasive plant in need of additional information to determine its true status” (Georgia Exotic Pest Plant Council, 2017). Although listed as invasive in California (Swearingen and Bargeron, 2017), it is also considered as a “waif”, not being able to survive and reproduce without human help where not native (Plantright, 2017), and in 2016 its status in California was reconsidered and changed to being a species to watch, with a low risk of invasiveness as successful new introductions are rare, especially in areas that do not provide an ideal cool, moist climate (California Invasive Plant Council, 2017).

Villalobos et al. (2010) report that despite the high seed production and Pyracantha coccinea being established in abandoned agricultural fields in the Montpellier region of southern France, it has not become a widespread invasive. Although the conditions in these fields may promote its establishment and growth, seed predation and the lack of summer dormancy prevent it becoming a widespread invasive.

In Australia, the different Pyracantha species can form dense thickets and compete with the native vegetation, but they are not considered as invasive, but rather as potentially high-risk weeds only in some areas (Csurhes et al., 2016).

Pyracantha coccinea is a species with a low risk of introduction into hot tropical areas and a higher risk in temperate areas and high elevations in subtropical areas. It is adapted to temperate climates and will not do well in hot tropical areas (Csurhes et al., 2016; Dave's Garden, 2017). Its popularity as an ornamental has facilitated its introduction worldwide since the early 17^th century (Lesel, 1994). Also, its suggested use to provide fruits to birds at the beginning of winter enhance its risk of introduction in temperate areas (Sallabanks, 1993).

P. coccinea is found in rocky and steep areas, woodlands, coastal scrub, riparian areas, roadsides and borders of grasslands (Olmez et al., 2007; California Invasive Plant Council, 2017; PFAF, 2017). Members of the genus can be found in disturbed sites (Csurhes et al., 2016).

The Pyracantha species are hosts of Erwinia amylovora, which causes fireblight, a serious disease of apples and pears (Csurhes et al., 2016). Caution should be taken when members of the genus are present near apple and pear orchards (Csurhes et al., 2016).

Genetics

The chromosome number reported for Pyracantha coccinea is 2n = 34 (Flora of North America Editorial Committee, 2017). Germplasm resources are available at the USDA-ARS facilities (USDA-ARS, 2017). The species has DNA barcode information available at the Barcode of Life Data System (Barcode of Life Data System, 2017).

Cultivars and hybrids are available, varying by form, fruit colour and hardiness (Floridata, 2017).

Reproductive Biology

Pyracantha coccinea reproduces by seed and from stem cuttings and grafting (Dave’s Garden, 2017). In vitro propagation protocols are provided by Dong et al. (2017). The species is reported as being pollinated by bees (PFAF, 2017). The seeds germinate best after cold stratification for 90-120 days (Olmez et al., 2007; Missouri Botanical Garden, 2017a).

Physiology and Phenology

Pyracantha coccinea flowers during the spring; the fruits begin to develop during the summer and mature in the late autumn (Villalobos et al., 2010; Dave’s Garden, 2017). Best seed germination is obtained after soaking the seeds in water for 24 hours and with cold stratification for 90-120 days (Olmez et al., 2007; Missouri Botanical Garden, 2017a).The species is evergreen in mild climates, but semi-evergreen to deciduous in colder areas (Missouri Botanical Garden 2017a). It has a fast growth rate (Encyclopedia of Life, 2017).

Longevity

Pyracantha coccinea is reported as having a moderate life span, without further details (Encyclopedia of Life, 2017).

Environmental Requirements

Pyracantha species are best adapted to temperate Mediterranean climates (Csurhes et al., 2016). Although P. coccinea grows in areas with colder winters, it should be planted in areas sheltered from cold winds (Missouri Botanical Garden, 2017a). The species can survive in areas with temperatures down to -28.8 °C, although it is best suited to areas that do not get as cold as this (Dave’s Garden, 2017; The Spruce, 2017). It does not do well in hot tropical climates; it does grow in regions with average warmest-month of 26° to 30°C (Csurhes et al., 2016). It is reported in areas with an annual precipitation between 950 mm and 1350 mm. It is drought-tolerant; it prefers full sun, but will grow in shaded conditions. Its soil pH preference is mildly acidic (6.1 to 6.5), but it will grow at acid, neutral and basic soils (Dave’s Garden, 2017; PFAF, 2017). It is adapted to fine to medium textured soils, but will grow in other soils, if they are well-drained. It tolerates strong winds, but not maritime exposure; it is not fire resistant (PFAF, 2017).

Fungi and bacteria reported as affecting Pyracantha coccinea include Erwinia amylovora, Pseudomonas syringae pv. syringae, Spilocaea pyracanthae [Fusicladium pyracanthae] and Venturia inaequalis (Bobev et al., 2004, 2008; Gladieux et al., 2010; Encyclopedia of Life, 2017). According to Dave’s Garden (2017), the seedlings are susceptible to fungi in tropical climates.

Possible insect pests include aphids, lace bugs, mites and scales (Missouri Botanical Garden, 2017a; The Spruce, 2017). Specific species reported to affecting Pyracantha coccinea are Phyllonorycter leucographella and Eriosoma lanigerum (Walczak et al., 2010; Ortiz-Martínez et al., 2013).

Environmental

• Amenity
• Boundary, barrier or support
• Erosion control or dune stabilization
• Wildlife habitat

General

• Botanical garden/zoo

Human food and beverage

• Fruits

Ornamental

• garden plant
• Seed trade

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.

Chemical Control

Dikegulac-sodium (3000-6000 p.p.m.) and chlorflurenol treatments reduce shoot and foliage growth of Pyracantha coccinea (Cohen 1978). Simazin causes severe foliage injury (Ries et al., 1959).

Information about the seed germination requirements and seedling establishment of Pyracantha coccinea is needed, as is detailed information about its invasiveness and its effects on natural habitats, especially in tropical areas.

29/12/17: Original text by:

Jeanine Vélez-Gavilán, Universidad de Puerto Rico, Puerto Rico