Poa annua, or annual meadow grass (known in America more commonly as annual bluegrass or simply poa), is a widespread low-growing turfgrass in temperate climates. Notwithstanding the reference to annual plant in its name, perennial biotypes do exist.
It originated as an allopolyploid hybrid between Poa supina and Poa infirma.Collins pocket guide Grasses, Sedges, Rushes and Ferns. Fitter.R, Fitter.A, Farrer.A. 1995. page 54 Major chromosomal rearrangements after polyploidy have contributed to variation in genome size in Poa annua.
Description It has a slightly creeping, fibrous rootstock. The stem grows from high. It is slightly flattened, due to being folded rather than rolled.
The panicle is open and triangular shaped, long. The spikelets are stalked, awnless, long when flowering, and loosely arranged on delicate paired or spreading branches. Sometimes they are tinged purple.
The vivid green leaves are short and blunt at the tips, shaped like the prow of a small canoe. They are soft and drooping. Long sheaths clasp the stem. The leaves are smooth above and below, with finely serrated edges. Occasionally the leaves are serrated transversely.
The ligule is pointed and silvery, in comparison to common meadowgrass (Poa pratensis), which has a squared ligule, and Poa trivialis, which has a pointed but less silvery ligule.
The leaves are smooth above and below, with finely serrated edges. Occasionally the leaves are serrated transversely.
It is in flower all year around except for severe winters. The seeds ripen and are deposited 8 months of the year. The plant grows rapidly from seed, flowering within 6 weeks, seeding and then dying.BSBI Description retrieved 10 December 2010.
Distribution and habitat It is a common weed of cultivation, known in the Americas as annual bluegrass. It occurs as a common constituent of lawns, where it is also often treated as a weed, and grows on waste ground. Many golf putting greens, including the Oakmont Country Club greens, are annual bluegrass, although many courses have converted to creeping bentgrass (Agrostis stolonifera).
It has appeared on King George Island in the Antarctic South Shetland Islands as an invasive species,Antarctic ecology: Polar invaders, The Economist, Mar 6th 2012 as well as on Australia's subantarctic Heard and Macquarie Islands.
Taxonomy Poa annua is an allotetraploid hybrid species that is derived from P. infirma and P. supina parents around 50,000 years ago. P. annua and P. infirma are often confused and are believed to form a rare sterile hybrid.Grass Manual Treatment
Etymology Poa - derived from the Greek name for a type of fodder grass.Gledhill, David (2008). "The Names of Plants". Cambridge University Press. (hardback), (paperback). pp 50, 308
annua - Latin, meaning 'annual' or 'lasting a year'.
References
External links European Poa Database The Observers Book of Grasses, Sedges and Rushes. Frances Rose. pages 38–39 Kew gardens grass database Weeds friend or foe? Sally Roth. pages 86–87 BSBI Description