First of all, afaik what
fdisk -l / shows is normally not relevant for mounting. mdadm uses it for building RAID volumes and LVM uses it for scanning physical volumes, but in most cases the type which is set in the master boot record (the one you see with fdisk) is not used. The man page of mount says the mount uses the blkid library to determine the fs type. You can do the same:
/dev/sda1: UUID="7S4ZFy-8sXS-Xk3x-WRvK-Lczt-HDgo-YOKLM1" TYPE="LVM2_member"
/dev/vg00/lv1: LABEL="lv1" UUID="8c2a4ab6-aac6-43c2-9866-ee1c9c3a6f32" TYPE="ext4"
If this doesn't help (and I think in your system this is the case), you can try to figure out the type using the command
file -s. Examples from my machine:
file -s /dev/sda1
/dev/sdb1: LVM2 PV (Linux Logical Volume Manager), UUID: 7S4ZFy-8sXS-Xk3x-WRvK-Lczt-HDgo-YOKLM1, size: 1500299779584
file -s /dev/vg00/lv1
/dev/vg00/lv1: symbolic link to `../dm-19'
file -s /dev/dm-19
/dev/dm-19: Linux rev 1.0 ext4 filesystem data, UUID=8c2a4ab6-aac6-43c2-9866-ee1c9c3a6f32 (needs journal recovery) (extents) (large files) (huge files)
It is possible that blkid fails if the corresponding fs kernel module is not loaded...