You're running Ubuntu, and that operating system generally doesn't utilize HFS+.
That you're then asking this question implies you were intending to not do that, or that you were intending to run multiple operating systems within one GPT-partitioned disk.
I'm going to guess you wanted multiple operating systems.
If you had intended to partition your disk and to use various file systems within the partitioning, then the command(s) that were used to partition or repartition your disk were not what was probably intended. (And this presumes that the two systems share compatible boot paths; that's possible with a system that can coexist within Apple's Boot Camp or Ubuntu or another operating system booted as a guest within one of the add-on OS X virtual machine products. I don't know for certain that Ubuntu can coexist.)
To get OS X back onto this same volume, you'll need to figure out if you have a GPT and then what's in your GPT, and whether there's a partition large enough for OS X to exist, or whether you can repartition your GPT disk to allow OS X to be reinstalled or reloaded into the partition. Or you'll need to wipe the whole disk, and replace its contents with a freshly-partitioned disk, and then load a copy of OS X that's been recovered from backup or freshly installed from distribution. Or you'll need to provide another disk, and then partition and load an operating system (either Ubuntu or OS X) onto that as appropriate.
The tools for doing the repartitioning within Ubuntu are best discussed with folks more familiar with that operating system; I'm not sufficiently conversant to suggest tools for that. I'd suggest a forum specific to Ubuntu for that. The tools used to repartition the disks on OS X generally involve the Disk Utility tool, whether booted from DVD (Snow Leopard), from the USB key disk (Lion), from an external OS X disk, or potentially using Target Disk Mode from another OS X system. And the OS X tools for repartitioning are destructive; they generally don't save what's in the existing partitions, if you need to make an existing partition smaller.
The usual sequence (and the one that's easiest to describe) to establish the environment starts by wiping the whole disk, and establishing GPT partitions of the appropirate sizes using Disk Utility or its Ubuntu GPT-aware analog, and then loading the target operating systems into each. Alternatively, you can read the Boot Campe documentation, or review the documentation with the particular virtual machine product that you're going to choose and use on OS X for details of how to manage its guest operating systems.
Without some idea of your end-goal here (and where you're stuck in the current environment), it's hard to provide more specific suggestions.