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Grass Identification: The Tribes of Grasses 1 – Poeae

Here is the first of Dr M’s promised grass identification blogs on the Tribes of Grasses and starts with The Poeae because?  Well just because it seems logical, we ARE talking Poaceae after all!  The Poeae is the second largest tribe of British grasses after Aveneae which will be the subject of the next blog in this series.

Eleven British genera fall in the tribe Poeae and are characterised by an inflorescence which is either a branched panicle (e.g. Dactylis, Festuca and Poa) or a bilateral raceme with the spikelets arrange edgewise (as in Cynosurus and Lolium).

The spikelets have 2-many florets (flowers), the glumes are short and membranous, the lemmas are membraneous to coriaceous (leathery) and if there is an awn present (some members of the Poeae tribe have awns, some don’t) the awn is attached terminally on the lemma and is straight not bent.

Now this is actually quite helpful stuff, because if you find a grass which has 1 floret per spikelet you now know it can’t be in the tribe Poeae! Equally, if you find a grass with an awn which is attached dorsally to the lemma (i.e. on the back of the lemma) it can’t be in the tribe Poeae.

Of course you still have to work out which tribe your grass is actually in, and then work out which genus and species it is, but at least you know it’s not Poeae! And when all is said and done, you have to start somewhere!

Click on the images to get a better view.

Now here are some examples of species from the main British genera falling in the Poeae:

1. Cynosurus cristatus (Crested Dog’s-tail) – a common pasture and meadow grass with a one-sided, spike-like inflorescence bearing dimorphic spikelets – that is, fertile and sterile spikelets mixed together (check the inflorescence of Cynosurus with your hand lens and prepare to be amazed, these are fabulous spikelets!).
2. Lolium perenne (Perennial Rye-grass) – the commonest sown pasture grass, with a spike-like (racemose) inflorescence with spikelets arranged edge-wise to the axis.
3. Dactylis glomerata (Cock’s-foot Grass) – a common grassland and hedgerow grass, with inflorescence a branched panicle with spikelets gathered in one-sided clumps at the tips of the branches – forming chunky spikelets like a knobbly cock’s foot as the common name implies.
4. Briza media (Quaking Grass) – a chalk grassland species with inflorescence a branched panicle with characteristic quaking spikelets and lemmas with broad membranous margins (check these spikelets under your hand lens, Briza bears truly gorgeous spikelets!).
5. Festuca rubra (Red Fescue) – a common grassland species, the inflorescence is a branched panicle with ovate spikelets, lemmas rounded on the back and with short to medium terminal awns.
6. Poa trivialis (Rough Stalked Meadow-Grass) – one of the commonest grasses found in a wide range of habitats, the inflorescence is a branched panicle with ovate, flattened spikelets and lemmas keeled and without awns (this helps distinguish Poa from Festuca which are rather similar).
7. Puccinellia maritima (Saltmarsh Grass) – saltmarsh grasses with inflorescence a branched panicle not unlike Poa.
8. Sesleria caerulea (Blue Moor-grass) – quite widespread and abundant grass but only in limestone grassland in the north of Britain with inflorescence an oval or cylindrical, condensed panicle.
9. Catabrosa aquatica (Whorl-grass) – rather local grass of ponds, ditches, canals and streams, the whorled panicle branches are the main ID feature.
10. Vulpia bromoides (Squirrel-tail Grass) – annual of dry grassy places, festuca-like but with condensed panicle and lemmas with long terminal awns
11. Catapodium rigidum – annual grass of dry grassy places with inflorescence a condensed racemose panicle and with coriaceous (leathery) lemmas.

Next up in this series is Aveneae and with 21 genera in total prepare yourself for a Poaceous extravaganza!

Contact Dr M if you find this blog helpful or if there are other things you want to know about grass ID or plant ID in general, Dr M loves to hear from his followers!


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