Basically, the mirrorless interchangeable-lens cameras offer DSLR image quality in a much smaller package. The bodies are about the size of all-in-one compact digital cameras, but they deliver DSLR image quality because, with a few exceptions, they have DSLR-sized image sensors. Canon, Samsung and Sony mirrorless models, plus the Pentax K-01, use APS-C sensors; Olympus and Panasonic use Four Thirds sensors (17.3x13.0mm). The Nikon 1 mirrorless models use a smaller 13.2x8.8mm sensor, and the extremely compact Pentax Q and Q10 use a smaller 6.2x4.6mm sensor.
Mirrorless lens options are a key consideration for landscape shooters. There are fewer lenses available for these cameras and, of course, larger lenses reduce the compactness of the cameras, but the systems—body, lenses and accessories—are still more compact than even DSLR systems, and so easier to carry into the field.
Canon currently offers two lenses for its EOS M mirrorless model, 18-55mm being the widest, but the EF-EOS M adapter lets you use all EF and EF-S DSLR lenses on the camera.
Nikon offers a 10mm ƒ/2.8, plus 10-30mm and 10-100mm zooms, for the Nikon 1 series, plus the FT1 adapter, which lets you use DSLR lenses on the cameras.
Sony's widest lens for the NEX mirrorless cameras is a 10-18mm zoom, and there are two adapters that let you use Sony DSLR lenses (including the LA-EA2 adapter, which incorporates a continuous phase-detection AF system like the one in the SLT-A65 DSLR).
Olympus and Panasonic Micro Four Thirds mirrorless cameras can use all Micro Four Thirds lenses (Panasonic offers a 7-14mm zoom and Olympus offers a 9-18mm zoom), and adapters are available for regular Four Thirds System lenses.
Pentax's K-01 accepts the same K-mount lenses as the company's DSLRs (the widest non-fisheye is a 12-24mm zoom). The small-sensor Q and Q10 models aren't really landscape cameras.
Samsung's widest lens for its NX mirrorless cameras is a 16mm ƒ/2.4, but there's an adapter that lets you use K-mount DSLR lenses, as well.
Fujifilm offers a 14mm ƒ/2.8 wide-angle for its X-Pro1 and X-E1 mirrorless cameras, along with an adapter for Leica M-series lenses.
Actually, due to their short flange-back distances, mirrorless cameras can use just about any lens for which an adapter can be found.