Saturday, 7 September 2013

Agrostis gigantea - Black Bent

Grass of the Month for August  2013

Agrostis gigantea can be difficult to distinguish from other Agrostis's early in the year.

The individual spikelets are similar to other Agrostis spikelets - As in all Agrostises, the two glumes are longer than the single floret and normally enclose it.

Like other Agrostises, A gigantea has two glumes and one floret and
the lemma and the palea are both translucent.

 It is more of a lowland plant, where it can be a weed in arable situations.
The BSBI map shows it has not been found in the hectads east and north of Settle (mostly sheep grazed hills) - which perhaps explains why I do not see it often. - but it is common in the south.

As an arable weed it can be seen at fence boundaries, where it uses the fencing for support - it is a straggling pant. The fence also prevents the grass getting mown/ploughed up.

The emerging leaf is rolled, the stems are narrow, the blades are thin and narrow (2-7 mm wide), the ligule is medium to long,

It has a long ligule - this picture was taken at Tems Beck Giggleswick 30 June 2013

It has rhizomes.

Agrostis gigantea has rhizomes (Tems Beck)

It can be distinguished from other Agrostis's because:
Agrostis vinealis and Agrostis canina have very narrow leaves (less than 2 mm wide)
Agrostis capillaris (which has rhizomes) has has short ligules
Agrostis stolonifera (which has long ligules and blades 2-7 mm wide) has stolons not rhizomes. A stolonifera also has a rather small compact panicle with the panicle branches pointing up at an angle of 45 degrees.

As the year proceeds, A gigantea shoot grow longer and they branch 20 or 50 cm above ground with extravaginal branching - i.e. a side branch pokes a hole through the sheath and there are then two stems.

See a new shoot breaking though the sheath, 
on part of  the main shoot well above ground level.
(Tems Beck, 30 June 2013)

By flowering time (August) A gigantea has really big spreading panicles.

Here is a panicle. It is actually very big.
(Pot Hole Lane, Malham Tarn,  7 Aug 2013)
(See other months' grasses)

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