I haven't found a good reference for archaeological material, but this is the story for modern material:
Two-row has a single seed at each rachis node whereas six-row has three. The central seeds of six-rowed look similar to two-rowed seeds (symmetrical) but may have more of a 'waist' near the rachis attachment, whereas two-row tend to be plumper, and look a bit like the shape of the prow of a boat. Lateral six-row seeds tend to be thinner still, asymmetrical and to have a twist near the rachis attachment. Rachis material can be useful too - six-row rachis nodes tend to flare towards the top to accomodate the three seeds whereas two-row tend to be more parallel. Wiebe and Reid (1961) has nice photos for diagnosis of modern material.
The two-row/six-row character is under single-gene control, so you can easily imagine how a crop may be of mixed character. Komatsuda et al (2007) cloned the gene and the article has a good description about how it works.
There are some exceptional landraces endemic to Ethiopia, and probably Nubia, where things are a little bit different (partial, labile and occasional failure of lateral florets).
Regarding bere, there are old references that back up what you say - mixed two and six-rowed crops in Scotland (Sinclair, 1814).
Also bear in mind that floret failure due to temperature and drought stress may also disproportionally affect lateral florets, so in six-rowed material, the ratio of lateral to central florets may well be less than 2:1.
Komatsuda, T. et al. Six-rowed barley originated from a mutation in a homeodomain-leucine zipper I-class homeobox gene. PNAS 104(4): 1424-1429 (2007).
Sinclair, J. General report of the agricultural state, and political circumstances, of Scotland. 486-500 (Arch. Constable and Co. Edinburgh, Longman, Hurst, Rees, Orme and Brown London 1814).
Wiebe, G.A., and Reid, D.A. Classification of barley varieties grown in the United States and Canada in 1958 (Technical Bulletin No. 1224) 2-47 (U.S. Department of Agriculture 1961).
Jay Moore
-----Original Message-----
From: The archaeobotany mailing list on behalf of Merryn Dineley
Sent: Sun 5/4/2008 10:14 AM
To: [log in to unmask]
Subject: Two or six row?
Hello there, I have a question I have been wondering about a while now.
How can you tell, from grains found during excavations, that it was a
six row or a two row barley? What are the indicators?
A few years ago we grew some bere in my garden as part of some
experimental research and we got both six and two row growing side by
side. I obtained the bere from the Corrigall Farm Museum, Orkney. Harry
Flett had a field of it to demonstrate traditional crops and it was the
same situation in their field, both types together.
regards,
Merryn
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