According to Variety, the "Heathers" and "Little Women" star will play the human mother to half-Vulcan Spock (Zachary Quinto).
Ryder's casting comes one day after the announcement that Bruce Greenwood will play original Enterprise captain Christopher Pike in the Paramount franchise reboot. The cast's other established name is Eric Bana, playing the evil Nero.
"Star Trek" will begin shooting later this month with a cast that also includes Chris Pine as Young Kirk, Karl Urban as Young Bones, Zoe Saldana as Young Uhura, John Cho as Young Sulu, Simon Pegg as Young Scotty and Anton Yelchin as Young Chekov.
Fans of the franchise know that Spock has always been torn between two worlds, between his logical Vulcan half and his emotional human half.
Spock's mom, Lady Amanda Grayson, was previously played by Jane Wyatt.
Ryder was most recently seen in "A Scanner Darkly" and "The Ten." She has "Sex and Death 101" ready for release and she recently finished work on "The Last Word" and "The Informers."