Back

Cycases from Yorkshire Modern cycases grow exclusively in the tropics. They are to be seen as survivers of a group which had a tremendous 'flowering time' in the Mesozoic but which was pushed aside by the angiosperms. They were plants with a thick trunk and with a bundle of rigid, mostly pinnate leaves on top. There were, however, also plants with undivided leaves. The male cones consisted of densely packed scales bearing sporangia on the lower side. The female spikes were placed on top of the trunk and consisted of pinnate leaves with rows of seeds on both sides or they were a kind of elongated cones with scales with two seeds on each scale. By far the most common cycas is Nilssonia compta (click on the photo on the right). The leaves of this plant are divided in segments, which are sometimes unequal in width. To distinguish this species from other ones, the number of veins per cm (at the base of the leaflets) is an important data. Nilssonia compta counts about 15 veins per cm. The veins of this plant are unbranched, just like those in all other Nilssonia species. The photo on the left shows a cuticle with stomata of Nilssonia compta. Note the difference with the cuticle of Nilssoniopteris vittata. Click on the photo. Nilssonia tenuicaulis has long straight leaflets, covering the axis of the pinnate leaf at the base (click on the photo on the right). Nilssonia tenuinervis (click on the photo on the left) has undivided leaves and therefore resembles the Bennettitales plant Nilssoniopteris vittata very much. Luckily Nilssonia tenuinervis has unbranched secondary veins, while those of Nilssoniopteris vittata are one time forked. The cuticles are also different. Rather common in Cayton Bay is the seed Beania gracilis of Nilssonia compta (photo on the right). Complete fructifications are extremely rare. Deltolepis crepidota is the fossil of a small scale from the trunk of a Nilssonia plant (photo on the left). The shape of the scale is broadly triangular. Another Cycas-like plant, found by us, is Ctenis sulcicaulis (click on the photo on the right). This was a plant with firm leaves, characterized by transverse connections between the veins. Top