British NVC community OV20 (Poa annua - Sagina procumbens community) is one of the open habitat

Vegetation of open habitats in the British National Vegetation Classification system

This article gives an overview of the plant communities formed by vegetation of open habitats in the British National Vegetation Classification system.-Introduction:...

 communities in the British National Vegetation Classification

British National Vegetation Classification

The British National Vegetation Classification or NVC is a system of classifying natural habitat types in Great Britain according to the vegetation they contain....

 system. It is one of six communities characteristic of gateways, tracksides and courtyards.

This community is widely distributed in the lowlands and upland fringes of Britain.

There are two subcommunities.

Community composition

Two constant species are found in this community:

• Annual meadow-grass (Poa annua
  Poa annua
  Poa annua, or annual meadow grass , is a widespread low-growing turfgrass in temperate climates. Though P. annua is commonly considered a solely annual plant due to its name, perennial bio-types do exist. 'Poa' is Greek for fodder. It is one of the sweetest grasses for green fodder, but less ...
  
  )
• Procumbent pearlwort (Sagina procumbens
  Sagina procumbens
  Sagina procumbens is a species of flowering plant in the pink family known by the common name birdeye pearlwort. It can be found throughout the Northern Hemisphere and parts of South America. It is a common weed of many environments. It can be found in wild and disturbed habitat, especially moist...
  
  )

No rare species are associated with the community.

Distribution

This community is widely distributed in the lowlands and upland fringes of Britain. It is found in urban and suburban habitats, occupying crevices between paving slabs and brickwork on streets and pavements, and in courtyards, and also occurs in rural areas, around farms and domestic buildings, wherever there is heavy trampling.

This is the British equivalent of the Papaveri-Sileneetum noctiflori syntaxon

Phytosociology

Phytosociology is the branch of science which deals with plant communities, their composition and development, and the relationships between the species within them. A phytosociological system is a system for classifying these communities...

, first described by Diemont, Sissingh and Westhoff (1940) from the Netherlands but which is found widely throughout Europe.

Subcommunities

There are two subcommunities:

• the so-called typical subcommunity
• the Lolium perenne - Chamomilla suaveolens subcommunity