We have used pressure-area isotherms and grazing-incidence x-ray diffraction to study structures of Langmuir films of first-generation monodendrons with two or three peripheral alkyl chains. Unlike the structures observed in their bulk liquid crystalline mesophases, these multichain monodendrons form either a centered rectangular lattice with molecular axes tilted toward nearest neighbors or an oblique lattice with molecular axes tilted in low-symmetry directions.