In article . com,
wrote:

While the saps of Toxicodendron (poison sumac(h)s) are highly
allergenic for most people, do you have a cite that shows that all
other sumachs have "toxic burn" saps?

We do converse in odd places!

Not really. I have seen such references in gardening books, but they
are notoriously unreliable. Several people have witnessed it for at
least Rhus typhina (though at a MUCH lesser level), and I can for
Cotinus coggygria. I am not a 'sensitive' person. The last produces
very little sap, so the chances are low.

In my case, neither Rhus typhina nor Cotinus coggygria cause me as
much reaction as Toxicodendron diversilobum, though the course of
the reaction is similar. And they can penetrate only thin skin,
whereas the last gets through medium skin (but not thick). They
aren't much worse than Vinca major on me. And, in all of those other
cases, there is no toxin carried on the surface of the leaves, so
that it causes trouble only when pruning/removing and then the sap
gets on thin skin.

In my limited experience, a fair proportion of the effect of
Toxicodendron diversilobum is because the surface oil carries the
toxin. There are many plants whose sap is quite seriously irritant,
but which produce very little even when cut and none at all if merely
brushed against - they then get classified as non-toxic. I have
evidence that these include Humulus lupus.


Regards,
Nick Maclaren.