CHAPTER XXVII 



HYMENOPHYLLACEAE 



This Family includes two large and comprehensive genera, HymcnopJiyllnni 

 and Trichomancs. The former is represented by 231 the latter by 228 species. 

 Both have been variously sub-divided by different authors: but there is 

 no need to enter here into these systematic details, for the morphological 

 principles of their comparison are the present theme rather than their 

 detailed application ^ 



The Hymenophyllaceae are widely distributed, chiefly in moist and shaded 

 spots, throughout the tropics: they extend as stragglers northwards, but 

 more freely to the south, and there is a special centre of their prevalence in 

 New Zealand. In point of time the records are doubtful, though Ferns with 

 sori and sporangia of corresponding appearance have been traced from the 

 Upper Carboniferous onwards. Various fossils have accordingly been 

 described under the name Hymenophyllites: but Seward concludes from a 

 critical examination of them that there is no evidence which can be adduced 

 in favour of regarding the Hymenophyllaceae as Ferns of great antiquity-. 

 Nevertheless they bear anatomical and other characters similar to certain 

 Botryopterideae, while at least the position and nature of the sorus in 

 Hyinenophyllitcs qiiadridactylites (Gutbier), from the French Coal Measures, 

 shows that the general type of their fructification existed in the Primary 

 Rocks. An early record does not, however, seem essential to the view here 

 entertained that the Hymenophyllaceae originated from protostelic Sim- 

 plices, though it would readily accord with it. 



The shoot of these Ferns is sometimes upright and radial, with spiral 

 phyllotaxis, as in some species of TricJiomanes: more commonly it is creep- 

 ing and dorsiventral, with the leaves arranged distichously, and elongated 

 internodes, as in many species of Trichomanes and all of HynienopJiyllitni. 

 From the axis numerous roots arise in most species, but in some, and 

 especially in the section HemipJilebinm of the genus TricJionianes, no adven- 

 titious roots are formed. The hairs borne on the shoot are filamentous, but 

 sometimes stiffly branched as mechanical protections, as in TricJiomanes 

 (Fig.. 504, C). In some species o{ Hymenophylliun of exposed habit the leaf 

 is covered by a hairy felt, as in H. sericeum. Flattened ramenta are absent, 



^ The chief systematic works are cited in Engler and Prantl, Natiirl. Pflanzenfam, i, 4, p. 91. 

 Reference may also be made to Christensen's Index Filicum, pp. xiii to xvi, where the synonyms and 

 sub-genera are given. 



- Fossil Plants, vol. ii, p. 365. See also Kidston, Fossil Plants of the Carboniferous Rocks, Part IV, 

 1923, p. 279. 



