Poa annua

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 bio-types do exist.^[2] This grass originated as a hybrid between Poa supina and Poa infirma.^[3] Major chromosomal rearrangements after polyploidy have contributed to variation in genome size in Poa annua.^[4]

Poa annua as a weed in city and urban ecosystems

Poa annua as a turfgrass for use on golf course putting greens

Poa annua
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Monocots
Clade:	Commelinids
Order:	Poales
Family:	Poaceae
Subfamily:	Pooideae
Genus:	Poa
Species:	P. annua
Binomial name
Poa annua L.

Description

It has a slightly creeping, fibrous, rootstock. The stem grows from 15–25 cm (6–10 in) high. It is slightly flattened, due to being folded rather than rolled.

The panicle is open and triangular shaped, 5–7.5 cm (2–3 in) long. The spikelets are stalked, awnless, 1–2 cm (0.4–0.8 in) 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.^[5]

Etymology

Poa is derived from the Greek name for a type of fodder grass.^[6] Annua is Latin, meaning 'annual' or 'lasting a year'.^[6]

Distribution and habitat

It is a common weed of cultivation, known in the Americas as annual bluegrass.^[7] 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,^[8] 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,^[9] as well as on Australia's subantarctic Heard and Macquarie Islands.

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  Habit
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  Ligule is silvery and pointed.
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  The panicle is open and triangular shaped
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  Flowers
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  Clump of Poa annua on footpath stones