  The lanthanum-hydrogen system has attracted significant attention following
the report of superconductivity in LaH10 at near-ambient temperatures and high
pressures. Here, we present the results of our single-crystal X-ray diffraction
studies on this system, supported by density functional theory calculations,
which reveal an unexpected chemical and structural diversity of lanthanum
hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides
were produced, LaH3, LaH~4, LaH4+{\delta}, La4H23, LaH6+{\delta},
LaH9+{\delta}, and LaH10+{\delta}, and the atomic coordinates of lanthanum in
their structures determined. The regularities in rare-earth element hydrides
unveiled here provide clues to guide the search for other synthesizable
hydrides and candidate high-temperature superconductors. The hydrogen content
variability in lanthanum hydrides and the samples' phase heterogeneity
underline the challenges related to assessing potentially superconducting
phase(s) and the nature of electronic transitions in high-pressure hydrides.
