None of the allergens in cucumber have been recognised by the World Health Organisation, but it thought that the allergen responsible for causing allergic reactions are similar to proteins found in ragweed pollen.
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Cucumber.php
The allergy resources page for cucumber covers the key allergens, which allergic syndromes are linked to this allergy and other foods which are commonly cross reactive with cucumber.
There is also regularly updated links to useful websites specifically for cucumber allergies and the latest research papers on the topic.
If you have multiple allergies and are interested in how they are linked or want to find out more about food allergies outside the usual top 14 then you can follow me on Facebook or Twitter, where I share a food allergy card every day of the week.