Practice question

Equisetum arvense and relatives, sole living genus of class Sphenopsida or Equisetopsida, produce homospore tetrads where each spore bears two hygroscopic ribbon-like elaters derived from outermost spore wall exosporium layer splitting spirally. Elaters uncoil under dry conditions and coil tightly when moist, causing spores to clump together improving wind dispersal as aggregates and promoting cross-fertilization between bisexual gametophytes on ground. They also provide slight locomotion on substrate surface toward moist microsites favoring germination. While not directly involved in fertilization or nutrition, elater movement enhances establishment.