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Identifying grasses. It’s obviously a Brome, but which Brome is it ? First, we need to identify the genus (i.e. is it Bromus, or Bromopsis, or Anisantha or Ceratochloa ?). This is the lower half of Key H on p. 1033.
#6 Are the lemmas strongly keeled on the back (left) or not (right). Definitely not keeled, so on to #7
#7 Always a tricky one. Annual or perennial? Look at the roots and check for the absence of rhizomes. See if there are any non-flowering shoots. No rhizomes and no sterile shoots, so annual is the best bet. On to #10.
#10 Easy one to finish with, once you realise what the question is asking. Spikelets straight-sided, widening towards their tips (distally) (left) or spikelets ovate, narrowed towards the tip (right). Read this again, until the penny drops. Ovate and narrowed, so Bromus.
The key to the 10 UK species in the genus Bromus is on p. 1088. You need to know that caryopsis means grass fruit (lemma and with the ovary inside). #1 This question always stumps beginners, often so traumatically that they just give up. Let's go through it one phrase at a time.
We are looking face-on at the back of the palea. On the left, the lemma margins are wrapped around the caryopsis; on the right they are not. Ours are wrapped around (left).
The next part of the dichotomy is about the degree of overlap of adjacent lemmas on the rhachilla (the flower stalk). On the left you can see the rhachilla between the lowest of the lemmas, but not on the right (all the lemma bases are overlapped). Our plant is on the left.
The last part of the dichotomy is the trickiest. "Rhachilla disarticulating tardily" or "Rhachilla disarticulating readily". How on earth do we know the answer to that? Try to pull the lemmas apart using your fine-nosed tweezers. Hard or easy? Ours were hard to pull apart.
Wrap-around lemmas, visible rhachis and tardy break-up mean #2 rather than #3. Now it's easy. Spikelets big (12-20mm) or small (8-12mm). Ours are 15.5mm so we have Bromus secalinus (Rye Brome). It's an annual weed of arable field margins (killed by herbicides elsewhere).
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