XXXIX] PELLAEA 8i 



IV. The Cheilanthoid Group 

 This group includes, as in Christensen's Index, the genera Pellaea Link, 

 Doryopteris J. Smith, Notholaena R. Brown, and Cheilanthes Swartz. All of 

 these Ferns fall into the "Pterideae-Cheilanthinae" of Diels (E. & P. 1,4, 

 p. 2 5 5 ): but here we exclude Hypolepis, L lavca, Cryptogramme, and Plagiogyria, 

 as also Aspleniopsis Mett. & Kuhn. The last is probably an ex-indusiate 

 Aspleniwn, while the other four genera have been assigned their natural 

 places elsewhere, for reasons already stated at length in Chapters XXXV 

 and XXXVI, and in this Chapter. The difficulty that has been felt in drawing 

 a clear line between the central group of the Gymnogrammoid Ferns and 

 those associated with Cheilanthes, and more particularly between Gyinno- 

 granmie and Cheilanthes, is in itself a sufficient index of their probable near 

 affinity in descent. The Cheilanthoid group is characterised generally by 

 having superficial sori seated upon the distal region of the veins, but more or 

 less extended backwards from the margin, and sometimes appearing to 

 coalesce when mature. Here again the rachis is often black and polished, 

 and the rhizome bears dermal scales. A xerophytic character is prevalent 

 throughout the group. 



Pellaea Link 



This large genus may be held as the least specialised of the group, 

 though not necessarily on that account the most primitive. It consists of 

 Ferns with a creeping rhizome, bearing scales, and with leaves that are 

 variously branched, with glossy dark rachis, and segments often of a harsh 

 and rigid character, suggesting xerophytic conditions. The venation is 

 pinnate, but sunk in the opaque mesophyll: it is usually free, but sometimes 

 the veins anastomose, as in P. Holstii Hieron (Fig. 6^^, F). The sori are linear 

 following the veins, but near to their endings. When mature they appear 

 confluent, but in reality they are separate, not being united by a commissure. 

 They are covered by a continuous "involucre," which is the reflexed and 

 often membranous margin of the blade. The whole structure corresponds to 

 that in Adiantnni, except that here the veins and sori stop short of the 

 overarching margin (Fig. 636, E). 



The stelar structure in this, as in all of the related genera, is based upon 

 the solenostele: some species of Pellaea {P. atropnrpurea (L.) Link, and 

 falcata (R. Br.) Fee) are even included in Gwynne-Vaughan's list of typical 

 solenosteles. In other species, however, in which the leaves are placed nearer 

 together, the leaf-gaps overlap, with the result that the ring is twice inter- 

 rupted, a state explained by the reconstruction in Fig. 637. Each leaf-trace 

 arises as a single vascular strap, with three protoxylems, and sometimes this 

 primitive structure is retained throughout the length of the leaf (P. andro- 



BIII 6 



