Some Lower Carboniferous pteridosperm cupules bearing ovules and microsporangia

Abstract

Synopsis: Two pairs of detached fossil cupules from the Cementstone Group of the East Lothian coast are described. One pair (specimen 1) contains 16 ovules agreeing with the seed genus Hydrasperma Long as well as 8 microsporangia containing spores. The second pair (specimen 2) has neither ovules nor microsporangia.The ovules present in specimen 1 have about 9 free apical tentacles and as many longitudinal ridges on the bodies of the ovules. The central column is very well developed, about as long as the ovule body and obconical in shape. In it some of the cells have bars of thickening on the walls like transfusion cells. Each cupule-pair has a common stalk which divides to become the two inverted cupules. In specimen 1 each cupule has a wall consisting of two valves united above but subdivided into tapering lobes below, i.e. distally. Ovules are borne below the concave upper region of each cupule (sessile laminar placentation). In this specimen each cupule-valve is subdivided into two smaller portions, one of which bears 8 microsporangia. The latter appear to be terminal and reflexed and almost sessile.The laminar placentation in Hydrasperma supports the view that this type of placentation in angiosperms is primitive and the bisexual cupule-pair here described suggests that the primitive fertile fronds from which cupules (and presumably carpels) evolved were originally capable of bearing both mega- and microsporangia.