jhn7's picture

Primrose - thrum form?

Observed: 17th March 2011 By: jhn7
S159 Neighbourhood Nature - course complete
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I've been searching for this form since finding out about pin and thrum from my first primrose observation.

Species interactions

No interactions present.

Species with which Primrose (Primula vulgaris) interacts


anonymous spotter's picture

The answer -

is in the anther(s)! I'm also struggling to tell which this is.
I learned about pin-eyed and thrum-eyed morphs in school botany classes, but even back in 1970 I doubt if any of us (including the teacher)knew what a thrum was.
"thrum (n)
1. a. Fringe of warp threads left on a loom after the cloth has been cut off.
b. One of these threads.
2. A loose end, fringe, or tuft of thread.
3. (Nautical) Short bits of rope yarn inserted into canvas to roughen the surface."

jhn7's picture


Any of the definitions could lead to thread like bits (of anther) visible at the top of the 'tube' bit (I'm sure there is a technical term for that too)! You are a fount of knowledge - thanks!

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AlanS's picture


Unless there are very unusual genetic forces at work, the ration of pins to thrums in any large, natural population of primroses should be approximately 1:1. (To be precise, a small excess of pins over thrums, but at most a few percentage points.)

Consequently, it should be easy to find both pins and thrums any time there is an established primrose population.

And yes, the arrangement of stamens could be said to resemble the end of a weaver's thread or so I have assumed.

Similar situation in cowslips:


Carl Bullock's picture

I know that pin to thrum is

I know that pin to thrum is meant to be 1:1 but so far I've always found that pin plants are far more plentiful then thrum... probably just a coincedence more then anything but interesting all the same.

jhn7's picture

That is what I have found too!

Yes, interesting! I suppose it depends how big the 'large natural population' is . 'My' wood is 8 hectares with primroses growing in separated areas, often just one clump on its own quite isolated. Perhaps this is not dense enough to show the usual ratio.

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