Notes on sporangia and spore masses containing tetrads or monads from the Lower Devonian (Lochkovian) of the Welsh Borderland, U.K.

A small number of very fragmentary sporangia containing tetrads are described using light, scanning and transmission electron microscopy as part of a study on diversity and disparity in Lower Devonian (Lochkovian) vegetation in the Welsh Borderland. The dispersed genus for permanent sculptured tetrads, . Acontotetras, is recorded in two isolated discoidal sporangia, one of which has a similar sporangial wall construction to that in . Cooksonia, the other with a non-cellular covering reminiscent of the recently described . Lenticulatheca and . Paracooksonia. Conversely, the dispersed spore genus for permanent, enveloped laevigate tetrads, . Cheilotetras, is found within two sporangia with valvate construction. Another example of the latter contains unique sculptured monads. Further diversity is exemplified by spore masses containing tetrads belonging to . Velatitetras and . Cheilotetras, but some evidence of splitting in specimens of the latter genus led to discussion on the state of maturity of the . in situ spores, and as to whether or not the dispersed palynomorphs would have been so as permanent tetrads or trilete monads. Such studies add to diversity, although a dearth of well-preserved specimens preclude erection of new taxa, and to disparity in local Early Devonian vegetation that was dominated by plants of very low stature.