For a while, it wasn’t clear how payments startup Leaf would get the distribution it needed to compete against Square and others trying to reinvent point-of-sale technologies for small and medium-size businesses. Just this summer, CEO Aron Schwarzkopf said in an interview that his young company had signed on fewer than 1, 000 customers.

Now we have an answer.

The Cambridge, Mass.-based startup has raised a $20 million strategic investment from Heartland Payment Systems, a publicly traded payments processing company that does $2 billion in revenue annually. Heartland isn’t Starbucks, the glitzy partner of Square, but it has a huge and valuable base of small-business customers to which it can introduce the Leaf system.

Like Square, Leaf makes software that helps small businesses sort, track and analyze their in-store transactions and access that information anywhere from the cloud. But unlike Square and others, Leaf actually makes and sells its own tablet that runs on a custom version of Android so it can have end-to-end control over the experience the merchant receives.

Yet despite wanting to own how the hardware and software interact, Leaf is attempting to build an open platform on top of which others can build apps. Leaf doesn’t actually process payments; it lets its customers choose from several payment processors, including Heartland and some of its competitors. But Heartland CEO Bob Carr said he is a fan of the open approach.

“We have done some work in POS before … but it’s not the most modern architecture so we began looking around at good platforms that were consistent with our architecture, ” Carr said in an interview. “We looked at many, many competitors of Leaf and felt like Leaf had the best architecture and most importantly had a shared philosophy where they have a platform that allowed merchants to do business with any number of vendors, and some of our competitors, so merchants could get exactly what they wanted.”