There are multiple species of grasses described on the World Health Organization Allergen Database.
The main allergen involved in grass allergy is the beta expansin protein. These are cell wall proteins which affect the airways.
Grass pollen occurs in the UK between April and September, peaking in June. This varies in different countries. It is considered to have high allergenicity.
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Grass.php
The allergy resources page for grass pollen covers the key allergens, which allergic syndromes are linked to this allergy and other foods which are commonly cross reactive with grass pollen.
There is also regularly updated links to useful websites specifically for grass pollen 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.