CHAPTER XXIV 



'ith a rhizome which 



GLEICHENIACEAE 



This Family is represented by 80 Hving species, referred in Christensen's 

 Index to two genera: Stroinatopteris which is monotypic, its single species 

 being native in New Caledonia: and Gleichenia with 79 species distributed 

 throughout the Tropics, whence they extend far southwards, but only in less 

 degree north, and they are absent from the northern temperate zone. This 

 genus has been divided into three sub-genera: (i) Dicninopteris{=^ Mertensia), 

 including flabellate forms which there is reason to regard as primitive: 

 (ii) Eu-Gleichenia, where the leaflets are contracted, probably in relation to 

 xerophytic conditions, and (iii) Platyzonia, with leaflets also contracted, 

 which is represented by a single, very peculiar species, native in North East 

 Australia. The Family is a very natural one, showing general uniformity 

 of character, though the details allow of the species being so arranged as to 

 illustrate important evolutionary steps. 



Among these Ferns a creeping habit is constant 

 deeply buried in Stroinatopteris, but in the rest 

 it spreads at or near the surface of the soil, 

 while it may sometimes take an ascending position. 

 Upon it the leaves are usually solitary, often with 

 long internodes, but sometimes more closely 

 grouped {Platyzoma). The axis dichotomises 

 frequently, the forking being independent of the 

 leaf-insertions (Fig. 472). The leaves, in which 

 the vein-endings are always free, are sometimes 

 simply pinnate {Platyzojiia and Gleichenia in the 

 sporeling state): but usually they show high 

 degrees of branching, together with a peculiar 

 straggling habit. Owing to the continued apical 

 growth and widely divaricating branching of the 

 leaves, these Ferns often form dense impenetrable 

 thickets at the margins of forests and on open 

 savannahs. 



The branching of the leaf has often been erroneously described as 

 dichotomous, but according to Goebel no species of Gleichenia has a 

 dichotomous leaf {Organography, Eng. Edn., ii, p. 319; also II Aufl., p. 1043. 

 191 8), though it is certainly the fact that equal forking (as in s. forma furcata) 

 does occur in Platyzonia (Thompson, Trans. Roy. Soc. Edin., p. 635. 1916), 

 and in Stromatopteris (Christ, Geog. d. Fame, Fig. 89). The error has arisen 

 B.n 13 



Fig. 472. Gleichenia linearis 

 (Buim.) Clarke, showing 

 dichotomy of the rhizome. 

 (Natural size.) 



