The　Streptophyta　include　unicellular　and　multicellular　charophyte　green　algae　and　land　plants.　Colonization　of　the　terrestrial　habitat　by　land　plants　is　a　major　evolutionary　event　that　has　transformed　the　planet.　So　far,　lack　of　genome　information　on　unicellular　charophyte　algae　hinders　the　understanding　of　the　origin　and　the　evolution　from　unicellular　to　multicellular　life　in　Streptophyta.　This　work　reports　the　high-quality　reference　genome　and　transcriptome　of　Mesostigma　viride,　a　single-celled　charophyte　alga　with　a　position　at　the　base　of　Streptophyta.　There　are　abundant　segmental　duplications　and　transposable　elements　in　M.　viride,　which　contribute　to　a　relatively　large　genome　with　high　gene　content　compared　to　other　algae　and　early　diverging　land　plants.　This　work　identifies　the　origin　of　genetic　tools　that　multicellular　Streptophyta　have　inherited　and　key　genetic　innovations　required　for　the　evolution　of　land　plants　from　unicellular　aquatic　ancestors.　The　findings　shed　light　on　the　age-old　questions　of　the　evolution　of　multicellularity　and　the　origin　of　land　plants.