Polycarpon tetraphyllum
(fourleaf allseed)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Polycarpon tetraphyllum (fourleaf manyseed); vegetative plant showing habit. Copyright ©Trevor James/Hamilton, New Zealand-2014	Habit	Polycarpon tetraphyllum (fourleaf manyseed); vegetative plant showing habit.	©Trevor James/Hamilton, New Zealand-2014
Title Habit Caption Polycarpon tetraphyllum (fourleaf manyseed); habit, whole plant flowering and fruiting. Copyright ©Trevor James/Hamilton, New Zealand-2014	Habit	Polycarpon tetraphyllum (fourleaf manyseed); habit, whole plant flowering and fruiting.	©Trevor James/Hamilton, New Zealand-2014
Title Inflorescences Caption Polycarpon tetraphyllum (fourleaf manyseed); massed inflorescences. Copyright ©Trevor James/Hamilton, New Zealand-2014	Inflorescences	Polycarpon tetraphyllum (fourleaf manyseed); massed inflorescences.	©Trevor James/Hamilton, New Zealand-2014
Title Flowers Caption Polycarpon tetraphyllum (fourleaf manyseed); close-up of open and closed flowers. Copyright ©Trevor James/Hamilton, New Zealand-2014	Flowers	Polycarpon tetraphyllum (fourleaf manyseed); close-up of open and closed flowers.	©Trevor James/Hamilton, New Zealand-2014

Identity

Preferred Scientific Name

• Polycarpon tetraphyllum (L.) L.

Preferred Common Name

• fourleaf allseed

Other Scientific Names

• Alsine polycarpa Crantz
• Mollugo tetraphylla L.
• Polycarpaea tetrphylla (L.) E.H.L.Krause
• Polycarpon tetraphyllum subsp. alsinifolium (Biv.) Ball
• Polycarpon tetraphyllum subsp. diphyllum (Cav.) O.Bolos & Font Quer

International Common Names

• English: four-leaf allseed; four-leaved allseed

Local Common Names

• : allseed; fourleaf manyseed; polycarpon
• : polycarpe a 4 feuilles
• Germany: vierblattriges Nagelkraut
• Italy: migliarina a 4 foglie
• Netherlands: kransmuur
• South Africa: Naaldvrug
• Sweden: Kransort; tusenfro

Summary of Invasiveness

P. tetraphyllum is a small and relatively insignificant annual plant. It is a widespread weed of cultivated and waste areas. Thought to be native originally to the Mediterranean region, P. tetratphyllum is now present on every continent except Antarctica. It is regarded as an invasive species in Australia, New Zealand, Japan, parts of South America and the USA, including Hawaii.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Caryophyllales
•                         Family: Caryophyllaceae
•                             Genus: Polycarpon
•                                 Species: Polycarpon tetraphyllum

Notes on Taxonomy and Nomenclature

P. tetraphyllum is described as one of about 16 species of the genus Polycarpon (Mabberley, 1997); however, Kool et al. (2007) pointed out the extensive synonymy, especially in the Polycarpon tetraphyllum group, suggesting that the number of taxa in the genus should be as few as eight. The Polycarpon taxa distributed in the Mediterranean region are largely ecotypes adapted to different environmental conditions rather than separate species (Kool et al., 2007). The same authors suggested that P. depressum, which grows in a relatively limited area in California and Mexico, may be the result of an earlier dispersal of a P. tetraphyllum lineage which had been isolated for some time and become adapted to the local environment. 

Description

Modified from Webb et al. (1988):

Annual, rarely biennial, or possibly perennial, taprooted herb. Stems glabrous, geniculate, erect to ascending, much-branched, 5-20 cm long. Leaves green or reddish, rarely purplish, glabrous, in whorls of 4 or rarely in opposite pairs, obovate to suborbicular, obtuse or shortly apiculate, petiolate, sometimes falling at fruiting, (2)-5-10-(15) × (1)-3-8-(10) mm. Stipules scarious, triangular to ovate, acuminate, 2-3 × 1-1.5 mm. Inflorescence many-flowered, lax or rarely compact. Pedicels about equal to calyx, equal or greater than the ovate acuminate scarious bracts. Sepals apiculate, hooded, green or reddish, rarely purplish, with scarious margins, 2-2.5 × 1 mm. Petals white, narrow-elliptic, entire, 1 mm long. Stamens 3-5, 0.5-0.7 mm long. Ovary 0.5 mm long; style 0.3-0.4 mm long, 3-lobed, deciduous. Capsule ovoid, about 2 mm long. Seeds curved, brown, finely papillate.

Plant Type

Distribution

The exact native range of P. tetraphyllum is obscure, but most authorities suggest it is native to southern Europe and the Mediterranean region (Weeds of Australia, 2013). Using DNA sequence data, Kool et al. (2007) found that the P. tetraphyllum clade is most diverse in the Mediterranean region, where they deduced that it probably originated. Weedy forms of the species have been spread to every continent except Antarctica.

P. tetraphyllum has been introduced to India, Japan, the Americas, Australia and New Zealand, parts of Europe and a few countries in sub-Saharan Africa.

Distribution Table

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.

History of Introduction and Spread

According to Thieret and Rabeler (2013), the spread of P. tetraphyllum to North America was partly due to its storage in ships’ ballast. Its seed is extremely small and could easily have been transported to North America and elsewhere as a contaminant in soil, dirt or vegetable matter taken there deliberately or accidently.

Historic records of P. tetraphyllum are known from Massachusetts in 1917 and Pennsylvania in the 1890s (Thieret and Rabeler, 2013).

According to Australia’s Virtual Herbarium (2013) the species was first found in Victoria in 1853 and in Tasmania in 1854. In New Zealand it was first recorded in 1854 (Webb et al., 1998).

In the UK, P. tetraphyllum has been known in Dorset since 1770 and south Devon since 1778 (Biological Records Centre, 2013). Populations can fluctuate dramatically and P. tetraphyllum has been rediscovered at some sites after an apparent absence of many years.

P. tetraphyllum was introduced to Belgium as a weed in containers with Mediterranean plants, and is now expanding rapidly in warmer microclimates of urban areas in that country.

Risk of Introduction

P. tetraphyllum has very small, dust-like seeds produced in large numbers. The transport of seeds to other countries or other parts of countries where P. tetraphyllum does not yet occur is therefore likely. Seeds can be transported as a contaminant in agricultural or horticultural seeds, in other agricultural produce or among the dust that tends to travel with passengers, their goods and luggage.

Habitat

P. tetraphyllum is generally a small weed of waste places, cultivated land and open pastures. In its native Mediterranean, P. tetraphyllum is found in woodlands and shrublands, deserts and montane vegetation (Danin, 2013).

In California, Hartman and Rabeler (2012) described its habitat as ‘disturbed shaded areas [and] roadsides’ below 450 m.

Biological Records Centre (2013) described its habitat in the UK as ‘open, sunny sites that are droughted in summer and relatively frost-free in winter. It grows with other therophytes on steep south-facing banks, on compacted shingle or sand, in bulb-fields and gardens and at the base of roadside walls.’ Clapham et al. (1962) described its habitat in the UK as sandy and waste places in the southeast (Cornwall, south Devon and Dorset), but added that suitable habitats for P. tetraphyllum in the UK were rare.

In New Zealand it is found growing in gravelly or sandy sites, coastal and inland areas, riverbeds, roadsides, railway ballast, seashore, waste land, cultivated land and grassland (Webb et al., 1988).

The ability of annual plants, including P. tetraphyllum, to colonise open habitats (because of their annual nature and wind-dispersed seed) and to capture resources effectively (because of the flat architecture of their rosettes) means they are more likely to occur in disturbed sites in temperate grasslands of the New England Tablelands of Australia (McIntyre et al., 1995). Disturbance by heavy grazing can increase the proportion of such annuals in these grasslands.

Habitat List

Biology and Ecology

Genetics

2n=32, 48, or 64 (Hartman and Rabeler, 2012).

Reproductive biology

The flowers of P. tetraphyllum are homogynous and automatically self-pollinated, and often cleistogamous (Clapham et al., 1962). In the Mediterranean region, Danin (2013) reported it flowering in almost every month of the year. In Britain it flowers in June and July (Clapham et al., 1962). In Australia P. tetraphyllum flowers in spring and continues into summer (Herbiguide, 2013).

In Australia, seed germinates in autumn to winter and plants then grow over winter through to summer (Herbiguide, 2013).

Kew Royal Botanic Gardens (2013) quoted an average 1000 seed weight of P. tetraphyllum as 0.05g. The seeds showed 100% germination at 10^o or 11^oC in 8 or 12 hours day length, although their age when tested was not mentioned.

A seed bank in Spain dominated by tiny seeds of P. tetraphyllum and Vulpia spp. contained up to 126,600 seeds m^-2 (Marañón, 1998; Olea and San Miguel-Ayanz, 2006). Lunt (1997) found seeds of P. tetraphyllum in the soil under intact remnants of Eucalyptus tereticornis woodland in temperate south east Australia, both in grassy forest or small grassland patches in the forest. P. tetraphyllum was not represented in the vegetation. More seeds were found in soil from the forest remnants than in soil from the grassland patches. Buisson et al (2006), working on abandoned fields in southern France, found seeds of P. tetraphyllum in few of the surface soil samples in winter (persistent seedbank), and even fewer in summer surface soil samples (transient seedbank).

Physiology and phenology

In Australia, P. tetraphyllum plants can be annual or biennial, with seed germinating in autumn to winter and the plants then growing over winter through to summer. They start flowering in spring and this continues into summer (Herbiguide, 2013).

Using old herbarium records, Buswell et al. (2011) investigated whether short-lived plants (including P. tetraphyllum) introduced to Australia before 1920 were evolving rapidly to the different conditions there. The only significant change in P. tetraphyllum was a reduction in plant height in specimens from the semi-arid region of New South Wales, but plant height in higher rainfall coastal New South Wales either did not change or increased over time. The authors suggested that this pattern ‘is consistent with the idea that the more arid environmental conditions in western New South Wales have selected for decreased height’ in this and a few other species.

Longevity

P. tetraphyllum is usually an annual, although there is a report of it as a short-lived perennial (Herbiguide, 2013). No information seems to be available on the longevity of seed in the soil.

Population size and structure

In Australia, P. tetraphyllum can produce a dense cover in moist, fertile areas (Herbiguide, 2013). Since individual plants tend to be quite small, this implies that plant densities can be very high in appropriate conditions. Gremmen and Halbertsma (2009) also found the species had high cover value at times in Tristan da Cunha, an island in the South Atlantic.

Means of Movement and Dispersal

Natural dispersal (non-biotic)

The seeds of P. tetraphyllum are very small and light and can be carried by air currents. However, since the parent plant is small (under 15 cm tall), long-distance dispersal of its seeds may be limited.

Vector transmission (biotic)

Calviño-Cancela et al. (2006) found seedlings of P. tetraphyllum emerging from the droppings of emu (Dromaius novaehollandiae). Twigg et al. (2008) reported the occurrence of whole or identifiable fragments of seeds of Polycarpon (perhaps P. tetraphyllum) in rabbit (Oryctolagus cuniculus) faecal pellets.

Buisson et al. (2006) assessed above-ground vegetation, seed rain, ant-borne seeds and seed banks on three abandoned fields in southeast France, at the margins between these fields and a remnant patch of native steppe vegetation of high environment value. P. tetraphyllum was present in 95% of the 990 quadrats used, but its seeds were only found in 2.8 % of the 1287 seed traps and in 0.4 % of the ant pitfall traps. Ants therefore seem to play only a small part in seed dispersal.

Accidental introduction

The seeds of P. tetraphyllum are tiny and can easily contaminate agricultural or horticultural seed, produce, machinery, or amongst the dust that tends to travel with passengers, their goods and luggage, and could easily be taken to new countries or to different parts of countries where the plant already occurs.

P. tetraphyllum is a wool alien (carried in wool used in manufacturing processes); in Massachusetts, USA, it has only been collected ‘in association with the waste dump of a nineteenth-century wool-carding factory’ (GoBotany, 2013). Hoste and Verloove (2009) described it as a container alien; it was introduced to Belgium as a weed in containers with Mediterranean plants.

Intentional introduction

Intentional introduction is very unlikely as P. tetraphyllum seems to have neither medicinal nor herbal uses and is a very small and inconspicuous plant.

Environmental Impact

Although usually considered a very small and insignificant weed, P. tetraphyllum can sometimes grow in very dense patches (Gremmen and Halbertsma, 2009; Herbiguide, 2013).

On the tiny South Atlantic island of Tristan da Cunha, Gremmen and Halbertsma (2009) reported that it is 'one of the species invading native dynamic habitats, thus contributing to the transformation of these plant communities into aliens-dominated vegetation.'

Social Impact

P. tetraphyllum is often regarded as a minor weed in gardens and occasionally in lawns, where it may reduce their aesthetic value.

On the tiny south Atlantic island of Tristan da Cunha, Gremmen and Halbertsma (2009) reported that ‘in gardens and arable land, as well as along road verges, it [P. tetraphyllum] locally reaches very high cover values. It is an abundant weed in the [potato] patches, and has a clear negative impact on food production.’ 

Risk and Impact Factors

• Proved invasive outside its native range
• Abundant in its native range
• Highly adaptable to different environments
• Pioneering in disturbed areas
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Has high genetic variability

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant

Similarities to Other Species/Conditions

In Australia, P. tetraphyllum resembles Crassula spp., Stellaria media, Cerastium spp., Portulaca spp., Anagallis arvenis, Montia spp., Sagina apetala and Euphorbia peplus (Herbiguide, 2013). All are low-growing, small weedy herbs, but most become taller or have much longer sprawling stems compared to P. tetraphyllum. Popay et al. (2010) identified Sagina apetala as the species most likely to be confused with P. tetraphyllum, but S. apetala has very narrow leaves in pairs and the flowers are less densely clustered than P. tetraphyllum.  

P. tetraphyllum var. diphyllum can be distinguished by leaves only paired (as opposed to being in fours), contracted inflorescences and 1-3 stamens, instead of 3-5 (Stace, 2010). 

Prevention and Control

Physical/mechanical control

Where P. tetraphyllum is established, Herbiguide (2013) suggested preventing seed set to control the plant.

Biological control

P. tetraphyllum is generally considered too small and insignificant to merit any major biological control effort.

Chemical control

The Novachem Manual (2012) lists 2,4-D ester for use in pastures, acetochlor in maize crops or terbacil in some fruit crops. There seems to be little information elsewhere on chemical control, other than the ubiquitous use of glyphosate in total weed control.

Control by utilization

Herbiguide (2013) suggests grazing the area where P. tetraphyllum is established. However, heavy grazing can increase the proportion of P. tetraphyllum and other small annual species in grassland (McIntyre et al., 1995). 

Gaps in Knowledge/Research Needs

Little information is available on the germination or longevity of seeds of P. tetraphyllum, nor on the slightly puzzling references to the plants being sometimes ‘perennial’ (Herbiguide, 2013). Nor is there information on how soon after germination the plants can flower and produce viable seed.

References

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Links to Websites

Contributors

15/11/13: Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.

Distribution Maps