SECTILE POLLINIA AND RELATIONSHIPS IN THE ORCHIDACEAE

The sectile state, in which pollinia are subdivided into units larger than tetrads, is one of several systematically important orchid pollin ium characters. We recognize two types of sectile pollinia, based upon form and arrangement of massulae. One type is found primarily in memb ers of Orchidoideae-Spiranthoideae, while the other characterizes epid endroid genera. Additional characters that have systematic potential a re massula dimorphism, caudicle composition, and degree of tetrad pack ing. Hollow sectile pollinia unite Arethusa and Calopogon; Stereosandr a and Epipogium have dissimilar pollina, but other characters support a close relationship between them. Tile sectile condition is interpret ed as resulting from a shift in the timing of cohesion of developing p ollen cells.