. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. CHAPTER XXXVI. GLEICHENIACEAE. This family is represented by about twenty living species, all of which are referred by some systematists to the single genus Gleichenia, though others separate off the monotypic genera, Platyzoma, Br., and Stromatopteris, Mett. The living species are distributed throughout the tropics, whence they extend far southwards, but only in less degree north, and they are absent from the northern temperate D Fig. 308. Gleichenia., Sw. § Mertensia, Willd. Scheme of branchi
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. CHAPTER XXXVI. GLEICHENIACEAE. This family is represented by about twenty living species, all of which are referred by some systematists to the single genus Gleichenia, though others separate off the monotypic genera, Platyzoma, Br., and Stromatopteris, Mett. The living species are distributed throughout the tropics, whence they extend far southwards, but only in less degree north, and they are absent from the northern temperate D Fig. 308. Gleichenia., Sw. § Mertensia, Willd. Scheme of branching of the leaf in the four sections of the genus. (After Diels, from Engler and Prantl, Nat. Pflanzenfam.') Among these Ferns an upright shrubby axis is occasionally found (Stroma- topteris), but usually there is a creeping rhizome, which sometimes takes an ascending position. Upon it the leaves are solitary, often with long inter- nodes, but sometimes more closely arranged (Platyzoma). The leaves are occasionally simply pinnate (Stromatopteris, Platyzoma); but usually they show higher degrees of branching, together with a peculiar straggling habit. The branching of the leaf has frequently been described as dichotomous; but according to Goebel no species of Gleichenia has a dichotomous leaf,1 the branching is always a monopodial pinnation ; the appearance of "forking" is the consequence of the two pinnules below the circinate but temporarily 1 Goebel, Organography, vol. ii., p. 319, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan and Co. , Ltd.
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