Poa trivialis - Rough Meadow-grass

Grass of the Month for April 2012

(See other months' grasses)

Poa trivialis grows

• beside woodland footpaths, 
• in gardens, 
• in species rich hay meadows, 
• in damp meadows that have been so heavily fertilised that they hold little else except Ryegrass and Poa trivialis, 
• beside streams
• in nettle patches 
• on roadside verges

Vegetatively, Poa trivialis is easy to recognise.
Well I think so
.
The above plant found on a woodland footpath makes a flattened tuft. If growing in a meadow you might  find just individual fine shoots threading through the sward, with the emerging leaf folded and the blades folded, and the sheaths compressed.

Can you see how the narrow shoots Trail along the ground? - they are Tiny and Trivial.

The shoots are very compressed. They lie flat against the ground and look Trampled on.

The underside of the blades are shiny (when folded, it is only the undersides that you see). With raindrops, they are so shiny they almost Twinkle

Get it?
Tiny, Trivial,  Trailing shoots that look Trampled on and have Twinkling undersides to the blades
Twinkling for Twivialis.

If there is sufficient light, the sides of the sheathsl  facing the light are Terra-cotta coloured (plum coloured), whilst the blades are Tree green  (Tree green means bright mid green - not bluish as in Poa pratensis or whitish as in Poa annua)

Later in the year some of the trailing shoots might root so then they become stolons.

The blades are  Tapering and thus Triangular - like a long isosceles triangle

The above photo of two vegetative blades is useful because as well as showing the tapering nature of the blade, it shows the characteristic vegetative features of nearly all Meadow-grasses:- tramlines (two central grooves) the boat shaped tip (with imagination).

It also show a  SHORT ligule.

"Short ligule?" you ask. "Doesn't Poa trivialis have a long ligule - to distinguish it from the short ligule of Poa pratensis?"

Answer:- the flowering shoot of Poa trivialis has a long ligule, but the vegetative shoots have short ligules.

Poa trivialis growing on the bank of the river Laver
near where it joins the Skell. Note Ground  Elder. see how they trail

The flowers?
They come out in May-July and  have "Christmas-tree panicles, just like the other Poas.  - It is the vegetative trainling shoots that are so distinctive...
But the flowering shoots, which start to grow in April,  grow vertically (even before the flower pokes out), and higher up the shoot they have LONG ligules, and rough sheaths - Hence the name    "Rough Meadow-grass"


Can you remember all the Tr adjectivies for Poa trivialis?
Trilling. Triumphant - Tremendous - trivialis - and the other ones?

(See other months' grasses)

Poa pratensis - Smooth Meadow-grass

Grass of the Month for March 2012

(See other months' grasses)

Photo of Poa pratensis taken on 28 January 2012 outside Church Hall

Poa pratenis between two paving stones at St John's Church Hall, Settle

This year I am "Wading through the Poas". Whilst I like to maintain that I can recognise most grasses any month, March proved hard. I drove around to favourite sites looking for Poa compressa, and expecting to see Poa trivialis and Poa pratensis everywhere. The Poa compressa was rather dead and undistinctive. The Poa trivialis - normally so common around here - was alsmost absent. I suppose all last year's growth had decomposed. However here are two photos I took at the end of January of Poa pratensis.

All the Poas have tramlines and boat-shaped tops.

I can tell it is not Poa annua (which is flowering now) because there are a lot of thick dead sheath bases and old leaves - implying this plant is a perennial, and the blades are thick textured and slightly bluish green, and it has short ligules..  Poa annua would not have many dead remains, the blades would be thin and whitish or mid green, and it would have bigger white ligules. Poa annua does not have rhizomes.

Poa pratensis has rhizomes - and it is relatively easy to guess that this plant between the paving stones may have rhizomes - the way the shoots are spaced along the crack with gaps between the tufts. If you dig it up you should see the rhizomes.

Poa pratensis has parallel sided leaves (unlike trivialis which has tapering leaves),
Poa pratensis has bluish green leaves (unlike trivialis which has shiny bright green or yellow green leaves)

The shoots of Poa pratensis  rise vertically from the ground (or almost so) and then the blades stick out at a wide angle to catch the sunlight

Poa pratensis and Poa humilis
Poa pratensis is extremely similar to Poa humilis  (Spreading Meadow-grass) formerly called Poa subcaerulea. Poa pratensis has tufts of shoots joined by rhizomes whereas  Poa humilis has single shoots.  Some books say that Poa humilis has tiny hairs at the base of the leaf blade - but I have found that both species have this.
Poa humilis can be found in mole hills in damp peaty soil. Poa pratensis is more likely to be found in cracks in dry walls. but there is a big overlap.
For the critical feature you need to have a flower:
Poa pratensis has one vein on the lower glume
Poa humilis has three veins on the lower glume

I will be teaching a grass identification course at Juniper Hall in ten days time.

(See other months' grasses)