Filicales and Gymnosperms, and known as the Cycadofihices, a group in which, curiously enough, the reproductive organs remained undiscovered for some time after the anatomy of the vegetative organs was sufficiently well known to afford clear evidence of their true affinities.
7rrepOv, feather, 7rrepis, fern), a name often used to denote the whole botanical class of Pteridophytes, including both the true ferns, Filicales, by far the largest group of this class in the existing flora, and the fern-like plants,.
The Equisetales (Horse-tails), the Lycopodiales (Club mosses), the Filicales (Ferns) and Cycadofilices, the Sphenophyllales and Cordaitales.
The Sphenophyllales are only known in a fossil state, while the Equisetales, Lycopodiales and Filicales include both living and extinct representatives.
It remains to be mentioned that the Isoetaceae have been regarded as more nearly allied to the Filicales than to the former, near which they are here placed.
The important bearing of this question on the relationship of the Ophioglossaceae to the phyla of the Filicales and Lycopodiales will be obvious.
Our knowledge of the extinct Filicales cannot be readily summarized, since it is in a transition state, owing to the recent evidence which has shown that many of the fern-like plants of the Palaeozoic period belonged to a group of seed-bearing plants derived from a filicineous ancestry.
Hydropterideae.-Two very distinct orders of heterosporous Filicales, the Salviniaceae and the Marsiliaceae, are included in this group. The difficulty of determining their exact relationship to the other orders of Ferns is increased by the more or less completely aquatic habit of the plants and the modifications and reductions in structure associated with this.
In the earliest land vegetations of which we have any sufficient record specialized forms of Equisetales, Lycopodiales, Sphenophyllales and Filicales existed, so that we are reduced to hypotheses founded on the careful comparison of the recent and extinct members of these groups.
As to the relationship of the Filicales to the other phyla, evidence from extinct plants appears to be wanting.
The most important positive evidence on this point indicates that the most ancient Gymnosperms were derived from the Filicales rather than from any other phylum of the Vascular Cryptogams. Extinct forms are known intermediate between the Ferns and the Cycads, and a number of these have been shown to bear seeds and must be classed as Pteridospermae.
In addition to the three classes, Equisetales, Lycopodiales and Filicales, under which recent Pteridophytes naturally group themselves, a fourth class, Sphenophyllales, existed in Palaeozoic times, clearly related to the Horsetails and more remotely to the Ferns and perhaps the Club-mosses, but with peculiarities of its own demanding an independent position.
On the present evidence it appears that the class Filicales was well represented in the Palaeozoic flora, though by no means so dominant as was formerly supposed.
Among the large number of Mesozoic Ferns there are several species founded on sterile fronds which possess but little interest Filicales, from a botanical standpoint.