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Can you tell whether a salix alba tree will produce male flowers or female flowers by looking at it, touching it or generally using your unaided senses? If not, is there any way to do that without specialized equipment or lots of expertise?

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Neat question. I wonder if there are any common trends / rules of thumb that hold true across many taxa for sexing dioecious plants? –  Oreotrephes Jan 19 at 16:01
    
DNA sequencing? –  shigeta Jan 22 at 20:18
    
@shigeta If you know of a way of sequencing DNA by looking at trees, please post an answer. But do make sure that after applying your method I can actually tell what the flowers will be. I've never sequenced any DNA. –  ymar Jan 22 at 20:51
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Not answering your question as written, but you can always try looking around the base of the tree to find fallen fruits/flowers from earlier in the year. –  Oreotrephes Jan 23 at 15:31
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2 Answers 2

up vote 4 down vote accepted
+100

I remember overhearing a botanist some 10 years ago, that he cannot tell male poplar from female when they are not flowering or producing seeds. Poplars and willows are related, so it is a weak indication for you, you will likely not find any visible features in willow neither. But it is an old information, too.
(Are you interested in DNA sequencing evidence or not ? I can look it up for you, but it seems your statement in comment question was ironical.)

EDIT: have just found an article which says: "In Salix viminalis, the sex of plants cannot be confirmed until the first time they flower." At that time, 1997, there were no DNA markers for plant sex detemination, but it is apparent, they did not know how to differenciate the sex of this willow just from morphology. This example is even closer to Salix alba than poplar. I find it even more likely now, that you will not find the morphological features.

( C. Alström-Rapaport, M. Lascoux, U. Gullberg. Sex determination and sex ratio in the dioecious shrub Salix viminalis L. Theoretical and Applied Genetics 1997, Volume 94, Issue 3-4, pp 493-497).

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Thanks for your answer, Barbara. Well, I'm generally interested in knowledge, and it might be useful for somebody, so there's no harm in posting that, and I'd be glad to learn. I just asked the question because I wanted to know if I could impress people by telling them, "Look, this is a lady willow," with as much wisdom about my looks as I could summon. –  ymar Jan 23 at 11:47
    
Thanks for the edit too. This seems to answer my question completely. I will wait a bit with accepting, but I find it unlikely that a better answer could show up. :) –  ymar Jan 23 at 21:54
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Data from year 2012: still unable to morphologically discriminate individuals before the reproduction age, plus no reliable DNA- based method, genetic basis for sex poorly understood. Source. The best is a DNA method, which predicts that Salix viminalis is a female with only 96 % accuracy. –  Barbara Jan 25 at 10:33
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Now, I know my obsession with this question is crazy :-D.

I took the suggestion of Oreotrephes. This is what to look for under the tree - friut and seeds:

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Source.

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