CHAPTER XLIV 



BLECHNOID FERNS 



This Family includes nearly two hundred living species, a fact that shows 

 its high success. They are distributed among ten genera, of which by far 

 the largest is Bleduunn with 138 species. The genera may be segregated 

 into four groups according to their soral features. The genus Bleclimun 

 forms, together with Sadleria, a central point from which the rest may be 

 held as derivative. Accordingly Blechnum will be examined first. The habit 

 of the Blechnoid Ferns is very various, some are creeping, some climbing, 

 some almost dendroid (Fig. 686). They are characterised by a stiff or 

 leathery texture of their foliage, suggesting xerophytic adaptation. They 

 show various degrees of that dimorphism which was a constant feature of 

 the Onocleeae: it is most marked in the type of Lomaria, now held as a 

 section of the genus BlecJumm. There is reason to believe this to have been 

 the original type, the segments of the sporophylls being narrow, and the 

 margins strongly incurved, as they are in Matteuccia. In the rest the sterile 

 and fertile leaves are more or less fully alike, and steps will be traced 

 explaining how this may have come about in the course of the evolution of 

 the tribe from the Lomaria-type. 



These Ferns were ranked by Diels as a Sub-Tribe Blechninae, under the 

 Tribe Asplenieae, For reasons already partly explained in Chapter XLIII 

 and to be developed further as the treatment proceeds, they will here be 

 held as a phylum distinct in origin from the Asplenieae, though showing 

 signs of evolution parallel to them. Borne upon an axis of various pose the 

 leaves are often simply pinnate, with open venation: but sometimes there 

 is a higher pinnation: various degrees of reticulation are also seen. The 

 common feature of them all is that linear coenosori take a parallel course, 

 one on either side of the mid-rib, while a vascular commissure below the 

 common receptacular line of each supplies them in a manner not unlike 

 that seen in Pteris. From these Ferns, however, they are phyletically 

 distinct (Fig. ^?)'j). Geographically the Blechnoid Ferns are very widely 

 spread, and many are tropical. A great preponderance of their species grow 

 in the Southern Hemisphere, and they are particularly plentiful in Polynesia. 



Blechnum Linn, emend. Mett. 

 In accordance with general opinion since the time of Mettenius the 

 genus Blechmm is accepted in its wider sense, as comprising three sub- 

 genera: (i) Loniaria, (ii) Eu-Blechnum, and (iii) Salpidilaena. Lomaria will 



