In its native range of Europe, northern Africa and Central and West Asia, P. coronopus is an inoffensive low-growing herb in coastal saline situations. It is rarely a weed of crops though Holm et al. (1979) list it as a ‘common’ weed in Spain. In recent years, however, it has been recorded as invasive in Australia and in California, forming dense mats which displace native vegetation, including endangered species in California (Weber, 2003; United States Fish and Wildlife Service, 2008a, b). Furthermore, it is reported as a weed problem in non-tilled orchards, irrigated pastures, and alfalfa and clover fields in California.
Plantago coronopus was named by Linnaeus and this name has survived, with no alternatives being proposed. Hence there are no synonyms listed, but it is a highly variable species and there are several recognized subspecies and many varieties described, differing in leaf shape, etc. P. coronopus subsp. commutata differs in being tetraploid and has previously been treated as a separate species, P. commutata.
P. coronopus may behave as an annual, a biennial or a perennial. The plant can develop axillary offsets, hence reproducing vegetatively. A rosette of leaves develops, remaining flat or largely close to the soil. Leaves are up to 20 cm long by 2 cm wide, variously entire or shallowly or deeply toothed, somewhat pubescent. Under saline conditions the leaves may show distinct succulence. Flowering stems are numerous from each rosette, up to 20 cm high, carrying a dense spike of flowers 2-5 cm long. Each flower is subtended by a bract and consists of four sepals, the two on the posterior side conspicuously keeled and hairy. Alternating with the sepals are four whitish transparent petals. The flowers are normally hermaphrodite, having four stamens with long filaments, and large yellow versatile anthers and a syncarpous ovary surmounted by a long, hairy simple style. However, male sterility does occur. The capsule has two lower chambers with two seeds each, while there is usually an upper chamber containing a single smaller seed. The larger seeds are black, shiny, boat-shaped and 1.0-1.5 mm long (mean weight 0.20 mg) while the smaller are 0.7-0.9 mm long (mean weight 0.13 mg). The larger seeds are released when the capsule dehisces, while the smaller seed is usually retained (Rowling, 1933).
Pollen in P. coronopus is highly annulate but not highly operculate. In P. lanceolata it is both, while three other species in Pakistan, including P. major differ in not being highly annulate (Al-Quran, 2004).
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.
There is some risk of introduction via trade in the seeds for cultivation as an ornamental but this is not extensive. The main risk would seem to be via the importation of grass seed from contaminated pastures.
In the UK, the species is found mainly in maritime habitats including the lower rocks immediately above high tide mark, rock crevices and ledges, the face of cliffs where detritus has collected, and grassy slopes leading up to, and above, the cliff face. It is also found on some fixed sand dunes and often in sandy soils when present inland (Dodds, 1953). Weber (2003) indicates occurrence in grassland, along rivers, in fresh and saline wetlands and on coastal dunes. Given its wide native range, however, the species is likely to inhabit a broader range of environments than reported here.
In California, USA, P. coronopus is a weed problem in non-tilled orchards, irrigated pastures, and alfalfa (Medicago sativa) and clover (Trifolium spp.) fields. It is also reported as a threat to two endangered plant species in California; Trifolium amoenum (US Fish and Wildlife Service, 2008a) and Astragalus robbinsii var. jesupii (US Fish and Wildlife Service, 2008b).
The genetics of P. coronopus are complex. The plant is normally diploid (2n=10), but in a detailed study, Böcher et al. (1955) found one strain with 2n=11 and a single hexaploid plant with 2n=30. They treat the tetraploid form (2n=20) as a separate species P. commutata, presumably corresponding to P. coronopus subsp. commutata. A range of sources quoted by Missourri Botanical Garden (2012) confirm most forms being diploid (2n = 10 +/-1 or 2) but subsp. commutata tetraploid (2n = 20). Mohsenzadeh et al. (2008) conversely found the coronopus species to be tetraploid and the commutatus species diploid, but admit that this does not agree with previous publications.
Paliwal and Hyde (1959) found that male sterility in P. coronopus was associated with a single extra chromosome which is largely heterochromatic, shorter, and not homologous with any of the other chromosomes. No male-fertile plants contained this B-chromosome. However, this finding was contradicted by Raghuvanshi and Kumar (1983) who found no relationship between B chromosomes and male sterility. Male sterility has been further studied by Koelewijn and Damme (1995b; 1996) and by Damme et al. (2004) who found that both nuclear and cytoplasmic genes are involved in the inheritance of the male sterile character. They describe the nuclear (restorer) genetics of two cytoplasmic types. In both types, at least five multiple interacting nuclear genes are demonstrated, three with dominant and two with recessive restorer allele action. Intermediate partially male sterile plants can also occur (Koelewijn and Damme, 1996).
Other studies on the genetics of P. coronopus include a genetic diversity analysis of Plantago species and their interspecific hybrids through RAPD markers (Samarth and Vala, 2012) and the interspecific hybridization and induction of variability in Plantago species (Samarth and Fougat, 2012).
P. coronopus is self-compatible (Samarth et al., 2009) but protogynous, meaning that the ovaries are receptive before pollen shedding (Bos, 1992). This facilitates out-crossing.
The large seeds are shed in the autumn and germinate almost immediately. The small seeds are retained in the capsule and although they are capable of germinating immediately, their germination is generally delayed (Rowling, 1933; Braza and Garcia, 2011). The seeds differ also in the fact that the larger seeds develop mucilage on wetting while the small seeds do not. One consequence of this is that the larger seeds rapidly sink in water while the small ones float indefinitely (Rowling, 1933). There may be an initial dormant period, which is longer, up to two months, at higher temperatures. Germination occurs between 10 and 25°C. This may require light. Germination of P. coronopus subsp. crassipes was 96% after 72 h at 20°C in light, but only 2% in the dark (Shem-Tov et al., 1999). Rowling (1933) also showed that light was needed in May, but there was little difference between dark and light germination in September.
Male steriles produced more (41% to 148%) and heavier (12% to 22%) seeds than hermaphrodites (Koelewijn and Damme, 1996). In the field, the contributions of seed size variation (15%) and inbreeding (9%) combine with 48% higher seed production to give a total fitness advantage of 70% to male steriles relative to hermaphrodites. This is probably sufficient for maintenance of gynodioecy under the nuclear-cytoplasmic inheritance of male sterility (Koelewijn and Damme, 2005).
Germination is reduced under saline conditions and completely prevented in 0.2 M NaCl solutions (Luciani et al., 2001). The importance of mucilaginous seeds for the survival of the plant species under desert conditions is discussed by Gutterman and Shem-Tov (1996). The mucilage causes the seeds to stick to the crust of the desert soil and prevents the seeds being washed away by showers.
Physiology and Phenology
The relative growth rate (RGR) during the vegetative stage is 300 mg g-1d-1 and drops at the initiation of flowering buds to 60 mg g-1d-1, a fivefold reduction. The initiation of flowering is stage-dependent. After the formation of about 14 leaves, plants start to form flowering buds, independent of weight or leaf size (Koelewijn, 2004a). Seed size effects lasted until the end of the experiment and were reflected in all morphological measurements. The proportion of small verses large seeds is influenced to some degree by the environment (Braza et al., 2010). When grown intermixed, selfed offspring were always inferior to their out-crossed relatives (Koelwijn, 2004b).
In east Poland (Sotek, 2007) populations of P. coronopus are mainly composed of perennial plants with a significant proportion of biennial and a small contribution of annual plants. The shorter cycle was characteristic of the individuals growing in the conditions of lack of competition or strongly limited competition of the co-existing plants.
Under desert conditions P. coronopus showed plasticity according to the day length; plants under long days were larger and produced more seeds that germinated to higher percentages (Shem-Tov and Gutterman, 2003).
Established plants may apparently survive for several years, while Dodds (1953) refers to high germination from 3-year-old seeds.
Dodds (1953) reported a number of associations in a range of habitats: in salt marsh - Armeria maritima, Glaux maritima, Plantago maritima, Cochlearia officnialis and Triglochin maritime; and in transitional salt marshes or dunes - Agrostis stolonifera, P. maritima and G. maritime; in less saline conditions a much wider range of species was recorded.
In the Swina valley, Poland, extensive grazing by horses and cattle on salted meadows contributes to the protection of 21 plant species growing there, including a rare stand of P. coronopus (Warda and Rogalski, 2004).
P. coronopus favours situations with light sandy soils and high light intensity; withstanding high summer temperatures and moderately low rainfall. It is adapted to highly saline conditions (Apaydin et al., 2009). A study recorded the salinity threshold of P. coronopus being reached at 25% of sea water levels and growth was strongly depressed by higher salinities (Koyro, 2006).
Growth stimulation by carbon dioxide enrichment beyond close-to-current concentrations is only likely to be seen under nutrient-rich conditions in semi-arid and possibly other drought-stressed grasslands (Grünzweig and Körner, 2003).
Natural enemies of P. coronopus include the fungal pathogen Cadophora luteo-olivacea, which occurs in Spain (Agustí-Brisach, et al., 2011) and the ants Messor barbarus in France (Detrain and Pasteels, 2000) and M. rugosus in Israel (Gutterman and Shem-Tov, 1997). These authors noted that the larger mucilaginous ombrohydrochoric seeds were less likely to be taken by the ants. Lepidopterans Metzneria littorella and Phthorimaea plantaginella, the coleopterans Ceuthorhynchidius dawsoni and Mecinus collari and the dipteran Phytomyza plantaginis are all listed by Dodds (1953) as affecting P. coronopus in the UK.
Dodds (1953) also recorded that rabbits (Oryctolagus cuniculus) graze on the plants, especially the more succulent forms in the regions of salt marshes. Soay sheep (Ovis aries), goats (Capra hircus) and ponies (Equus caballus) have also been recorded as grazing on the succulent form.
While the larger, mucilaginous seeds are adapted to stick where they fall onto wet soil, the smaller seeds may be carried in the capsule by wind or water movement.
Presumably P. coronopus could be accidently transported as a grass seed contaminant and also in garden waste. New infestations of P. coronopus subsp. commutata in south Germany and Austria have been associated with the use of salt on roads (Gerstberger, 2001).
P. coronopus is available from some commercial suppliers as an ornamental or salad plant, but to what extent this has been responsible for its spread is not well documented.
In California, USA, P. coronopus is a weed problem in non-tilled orchards, irrigated pastures, and alfalfa and clover fields where mowing is used for weed control. Although slow to establish, P. coronopus is difficult to control when mature because of its extensive crown system.
It is a possible alternate host for the grapevive pathogen Cadophora luteo-olivacea (Agusti-Brisach et al., 2011).
It has been reported as forming dense mats that compete with native species and impact upon two threatened species in California, the showy Indian clover (Trifolium amoenum) (US Fish and Wildlife Service, 2008a) and Jesup's milkvetch (Astragalus robbinsii var. jesupii) (US Fish and Wildlife Service, 2008b).
P. coronopus is regarded as an environmental weed in Victoria and Western Australia (Queensland Government, 2012). Weber (2003) indicates it is invasive in Australia, but it has proved difficult to confirm the basis for this classification.
P. ovata (important as a medicinal plant in India) and P. lanceolata differ in having somewhat more erect, entire leaves and shorter inflorescences. The widely common P. major and P. media have much broader 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.
Control measures suggested for ornamental and perennial crops include cultivation, cover crops and the use of mulch (UC-IPM, 2012).
Isoxaben, a relatively new broadleaf pre-emergent herbicide, has been effective in limiting germination of P. coronopus in turfgrass and some ornamental crops. Post-emergent 2,4-D, triclopyr, MCPA, and mecoprop can control seedlings, but control of established plants is much more difficult. For established plants, 2,4-D works best while triclopyr, MCPA, and mecoprop will only reduce vigour. Repeated applications to perennial plants with products containing 2,4-D or triclopyr can be helpful (UC-IPM, 2012). In lucerne or alfalfa, pre-emergence treatment with hexazinone has been successful. Glyphosate can be effective in plantation and orchard crops.