LYCOPSIDA 53 



tomy of Protolepidodendron are difficult to make out, but 

 there appears to have been a sohd three-angled protostele 

 in the centre, with some suggestion of a mesarch proto- 

 xylem. 



Whether Aldanophyton was really a member of the Lycop- 

 sida cannot be determined with certainty, for no fertile 

 portions of the plant have been described. It had stems up to 

 13 mm in diameter, clothed with narrow leaves up to 9 mm 

 long and, although the preservation of the specimens leaves 

 much to be desired, one published photograph looks not 

 unlike Fig. 8E. Whatever its true affinities, this plant is an 

 important discovery, for it seems fairly certain that it was 

 a land plant and it therefore pushes further back into 

 antiquity the origin of land plants by some 200 million 

 years. 



Lycopodiales 



This group contains two genera of living plants, Lycopodium 

 ('Club-mosses') and Phylloglossum, and one fossil genus, 

 Lycopodites. Of the 200 species of Lycopodium, the majority 

 are tropical in distribution, but some occur in arctic and 

 alpine regions. Phylloglossum, by contrast, is monotypic and 

 the single species, P. Drummondii, is restricted to New 

 Zealand, Tasmania and the south-eastern corner of 

 Australia. Not only do the various species of Lycopodium 

 occur in widely different cHmatic regions ; they also occupy 

 widely different habitats, for some are erect bog-plants, 

 others are creeping or scrambling, while yet others are 

 pendulous epiphytes, and this wide range of growth form is 

 paralleled by an extremely wide range of anatomical 

 structure. Indeed, some taxonomists have suggested that the 

 genus should be split into at least four new genera, so differ- 

 ent are the various species from one another. Whatever their 

 status, the following sections and subsections of the genus 

 are recognized by most botanists. ^^ 



