Novel structure of placenta in a lycophyte

Lycopodium obscurum has a subterranean, mycoheterotrophic gametophyte that nourishes the embryo for several years. An examination of an embryo in an underground gametophyte by Renzaglia and Whittier reveals a massive foot with ultrastructural variability comparable to that across major clades. The intergenerational zone in unlobed regions shows unidirectional transport of materials toward the foot. Lobed, more mature areas contain degenerated gametophyte cells that lack wall ingrowths and sporophytic transfer cells. They conclude that placental features in Lycopodium reflect a dynamic, invasive and long-lived foot, and the unique reorientation of all embryonic regions during development. Homoplasy in transfer cell appearance and location is explained by diverse patterns of embryology across archegoniates.