Gametophyte Development in Latin American Horsetails

HIAUKE, R. L. (Univ. Rhode Island, Kingstoni, R.I.). Gametophyte development ill Latin American horsetails. Bull. Torrey Bot. Club 96: 568-577. 1969.-The gametophytes of the three Latin American species of Equisetum are described. One, E. giganteum, is normally bisexual, and produces both archegonia and antheridia simultaneously from the same meristem. Another, E. myriochaetum, produces initially some antheridial and some archegonial gametophytes. The latter, with age and in the absence of fertilization, cease bearing archegonia and develop antheridial lobes. The third species, E. bogotense, also produces unisexual gametophytes, but these are dimorphic and were never observed to change sex. Thus there appears to be a series illustrating development from a primitively bisexual condition to a stable unisexual condition through an intermediate plastic unisexuality. It is suggested that this may have been the pathway followecl by both heterosporous vaseular plants andl seed plants in their evoluLtion.