While probing the v7.1 update for the Google app, Cody discovered an image of a flower titled ic_pollen_count.png. It was pretty clear that Google was planning to implement some sort of pollen forecast in search at some point, and now it's been made official.
In a post on Google's blog, The Keyword, Associate Product Manager Nisha Masharani wrote about collaborating with The Weather Channel to display pollen data directly in the Google app. You'll get a description of today's pollen count, plus a forecast for each of the next 5 days. Tapping a link in the card takes you through to weather.com for more detailed information.
There will also be an option to turn on updates for your area, meaning the Google app will notify you if the count is especially high where you are so you can take any necessary precautions. Simply search for "pollen count/forecast" and tap the Turn On button. According to Google's post, seasonal allergies affect one in five Americans, so this should be pretty useful for a lot of people.
This feature will likely be rolled out gradually as a server-side change, so don't panic if you're not seeing it in the app just yet.