Google's (NASDAQ:GOOG) (NASDAQ:GOOGL) Android operating system is dominant. It powers about 80% of the smartphones sold globally, and two-thirds of the tablets. That dominance has been driven by variety -- there are more than 18,000 different Android-powered devices for sale today, smartphones and tablets offered in nearly every size and at every price point.

And it's only getting more severe. According to OpenSignal's latest report, Google's mobile operating system is more fragmented than ever. That fragmentation helps ensure Android's popularity, but it also raises significant issues.

Samsung's share is slipping
Each year, OpenSignal releases a report on the state of Google's mobile operating system, based on the hundreds of thousands of Android users who have downloaded its free app. OpenSignal's data, then, is certainly not perfect, but it provides an interesting snapshot of the broader Android landscape.

Since it began releasing its findings in 2012, Android's fragmentation has increased almost every year. In 2012, Samsung (NASDAQOTH:SSNLF) manufactured about 40% of the Android devices OpenSignal queried. That rose to nearly half (47.5%) of Android devices in 2013, before slipping to 43% last year. Samsung's share fell once again this year, down to a new low of 37.8%. That's not particularly surprising, and it corroborates the recent trends in the mobile market: The rise of low-cost Android competitors have pressured Samsung's smartphone sales and its profits.

Xiaomi has often been cited for Samsung's woes, but the situation appears far more complicated. OpenSignal saw a total of 1,294 distinct Android brands this year, up from just 599 in 2012. In total, OpenSignal saw 24,093 different devices, up from 11,868 in 2013.

The fragmentation problem
Android's high degree of fragmentation poses numerous challenges, both to developers and to users. The recent Stagefright issue provides a perfect example.

Stagefright is a software bug that affects newer versions of the Android operating system. Simply sending a certain text message to a vulnerable Android phone can allow an attacker to take control of the device, accessing it remotely.

The most popular Android phones have already received security updates that negate Stagefright, but many Android handsets remain unpatched. The decentralized nature of Android forces device manufacturers (and in some cases wireless carriers) to take charge of software updates themselves, rolling them out as they see fit. Given the sheer number of different Android manufacturers and handsets, it seems likely that some phones may never be updated.

This stands in sharp contrast to iOS. Apple (NASDAQ:AAPL) limits the number of different iPhone and iPad models in existence and handles all software updates itself. iOS has suffered from its share of security flaws, but iPhone buyers can take solace in the knowledge that their devices will receive timely updates from Apple.

Beyond security, Android's fragmentation makes it less appealing to developers. Apps are often designed for Apple's iOS first, then ported to Android at a later date. The variety of screen sizes is a contributing factor. While iOS currently supports just six different screen sizes, OpenSignal found Android devices with dozens of different sized screens.

Over one billion devices
Android's fragmentation is a problem, but not a devastating one. There were over 1 billion Android devices shipped in 2014, and that number is likely to be higher this year. The upsides to fragmentation are clearly more significant than its downsides. 

Yet so long as that great degree of fragmentation exists, it gives Apple an opportunity to serve its large niche, offering a more robust experience to those who find its fewer models amenable.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns and recommends Apple, Google (A shares), and Google (C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.