Tuesday, August 07, 2012

studies in Deschampsia cespitosa (Tufted Hair-grass)

Tufted Hair-grass (Deschampsia cespitosa or caespitosa), one of the UK's commonest tall grasses. Also sometimes known as Tussock-grass, or Hassocks. Photos taken yesterday (Aug 7th 2012) in Swindon - these plants, obviously, are at the fruiting rather than flowering stage. 

Below: Detail of Above, showing the distinctive, more or less equidistant panicle-nodes with typically three or four branches.

In this rainiest of years, the mass of "upright" culms gets knocked down into matted (and damp-retaining)  bundles.

The large, dense tufts distinguish D. cespitosa from all other common grassland species except Tall Fescue (Festuca arundinacea), a plant that is nothing like so abundant though clearly on the increase. The tussocks of D. cespitosa are a darker green, with distinctively narrow, sharp-pointed leaves.

The upper surfaces and margins are very rough. Holding the blade between finger and thumb you can slide your hand upwards, but encounter a lot of resistance if you try and slide it downwards.

My hastily thrown-together theory is that the roughness acts to keep the blades well separated from each other, thus allowing maximum exposure to light, obviously an important factor in such a densely tufted plant.

A more mainstream (and experimentally demonstrated) explanation is that the roughness in this and other grasses is caused by high silica content, and the silica acts to deter insect herbivores. Livestock, too, generally find the grass unpalatable, though horses and rabbits will eat it if there's nothing else around.

Deschampsia, as you might guess, is named after a Frenchman, Louis Auguste Deschamps (1765-1842).  The grass does him honour but does not have any particular appropriateness to him; he was a botanist/ship's surgeon interested in the tropical plants he saw on his travels. He may have been the first European to see Rafflesia, but this is uncertain. His notebooks were impounded by the British when his ship was captured during the Napoleonic War, and I get the impression (from hasty Googling) that some material was permanently lost.

 I wonder how other people pronounce it. I go for an "English" pronunciation (dezz-champs-ia), but you might prefer a "French" one (day-shom-sia) or even a "Latin" one (dess-camps-ia). Let me know!

"Hair-grass", I'm guessing, refers to the slender branches of the panicle, which are even finer in other species of Deschampsia, such as Wavy Hair-grass (D. flexuosa). No connection with the aquarium plants known as Hairgrass, which are small Spike-rushes (Eleocharis species).

Deschampsia cespitosa has the honour of being assigned a special community in  the British Vegetation Classification system: MG9. "MG" stands for mesotrophic grassland, which more or less means neutral grassland. MG9 is characterically dampish, poorly-drained meadow and it always contains D. cespitosa, along with Yorkshire Fog (Holcus lanatus). Exactly what you can see here.



At 4:19 pm, Anonymous Anonymous said...

Actually it was named for Louis Auguste Deschamps. You can see the original publication of the genus at www.botanicus.org/page/394170

At 5:44 pm, Blogger Michael Peverett said...

Corrected, thank-you.

(My source had attributed it to another botanist, Jean Louis Auguste Loiseleur-Deslongchamps (1774-1849)).


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