CYCADOPHYTA, a term of convenience for all cycad-leafed plants, introduced by A. G. Nathorst. The great majority of such plants are extinct and of unknown fructification, but so far as discovered they are naked seeded or gymno spermous. The apposed gymnosperm group Coniferophyta is now also used for the living and fossil plants with foliage like that of pines, araucarias, etc. See CYCADALES; PALEOBOTANY.
Perforce any group of plants mainly fossil is homogeneous or natural only with respect to its foliage, the flowers and fruits of extinct forms being seldom determinable with certainty. The Cycadophytes thus include frond types ex tending from those with pinnules like the exist ing Zamia Wallisii a foot and a half long by a foot in breadth to very narrow linear forms. The double bifurcate condition in Cycas Micho litzii suggests easy transition toward Ginkgo (q v.). There may be a single midrib as in Cycas, but the appearance is often very fern like with parallel to dichotomous lateral veins. Venation is mainly dichotomous, with easy transition into typical netted venation such as that of the Jurassic Diayasamites. An inter esting intermediate form, cosmopolitan in the later Mesozoic, is the genus Ctenis. As now used, the Cycadophyta are not restricted to the pinnate, or even bi-pinnate fronds like Bowenia of the Malaysian region. Many of the species
had simple blades sparsely inserted on slender stems after the manner of dicotyls. Such may be arbitrarily included because their relation ship to forms with decided cycad foliage has been proved. (See description of Cycadeoidea and Wielandiella in CYCADALES). Theoretically the Cycadophytan blade of the Stangerites, Or the Taeniopleris type, must approach primitive dicotyl blades like those of the early Magnolias (Liriodendropsis). In the latter there is gradual increase in size of the sparsely set parallel veins with gradual invasion of the finer marginal net. That is, the actual vein bulk remains much the same, but the dis tribution of the veins as a supporting frame work is different and stronger—meeting the needs of varied environments and of lofty trees growing in the open.
A fairly searching, though necessarily alter native classification of the Cycadophyta taken as a vast complex of forms extending back to the Carboniferous Age, and constantly being added to in tile course of paleontologic dis covery, is the following: