Calcium-containing crystals have been found in the lumens of secondary tracheids in the rhizome of the woody fern Botrychium multifidum. These crystals are styloids with rough, pyramid-shaped ends. The crystals are usually single; however, conjoined or grouped crystals were also found. Crystal formation apparently has no constant relation to the pit membrane, but crystals of mature tracheids are often associated with the pit membrane or are located in the pit areas. Crystals were also located between the helical thickenings of the lumen walls. No crystal chamber or crystal sheath was found in association with the crystal body.