Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
Am J Bot. 2009 Jan;96(1):323-35. doi: 10.3732/ajb.0800295.
A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic.
苹果湾（温哥华岛）下白垩统（瓦兰今阶-豪特里维阶）植物群多样性显著，该植物群保存的种子植物处于一个重要的植物区系进化过渡时期，与最早的开花植物大化石出现的时间大致相同。化石被碳酸盐结核矿化，包括在杯状或心皮状结构内的四面体种子。这些封闭结构由伸长的厚壁组织细胞组成，具有螺旋加厚，外部逐渐变为几层薄壁组织，由一个侧生维管束血管化，缺乏表皮毛。它们显然通过瓣裂打开，释放紧密包裹的种子。种子与三叠纪的种子蕨 Petriellaea 相似，但年龄小 1 亿年，在大小、血管化、表皮解剖、种子附着和每杯状结构的种子数量上存在差异。这些新种子被描述为 Doylea tetrahedrasperma 属和种，暂时归入科瑞斯托苏目。倒置的杯状结构让人联想到外生植物的表皮，而不是心皮。与果实一样，杯状结构在成熟时张开以释放种子，从而预示了被子植物的几个方面。它们表明，在中生代，高级种子蕨类植物几乎完全将胚珠封闭，达到了接近被子植物的组织水平。
