SPORE MORPHOLOGY IN THE CYATHEACEAE. I. THE PERINE AND SPORANGIAL CAPACITY: GENERAL CONSIDERATIONS

Abstract

The literature on cyatheaceous spore morphology relative to the presence of a perine layer is reviewed, and evidence based on a sodium‐hydroxide assay is presented indicating that the outer scultpine layer in certain cyatheaceous spores is perine. Perine so defined characterizes Metaxya , paleotropical and certain neotropical species of Sphaeropteris , nearly all species of Alsophila , all species of Nephelea , and certain species of Trichipteris and Cyathea. It is lacking in Lophosoria , many species of Trichipteris and Cyathea , and all species of Cnemidaria. Two major patterns of spore number per sporangium in the family are reported. Lophosoria, Sphaeropteris, Trichipteris, Cyathea, Cnemidaria , and probably Metaxya are characterized by 64‐spored sporangia, whereas most species of Alsophila and all species of Nephelea are characterized by 16‐spored sporangia. The congruence of this generic distribution of sporangial‐capacity types with Tryon's phyletic arrangement of cyatheaceous genera supports the naturalness of his system. The intrasporangial germination of spores retained in dehisced and dispersed sporangia supports the suggestion that decreased spore number per sporangium in Alsophila and Nephelea may relate to the role of the sporangia as dispersal units. The decreased number of spores per sporangium is associated with a trend toward increase in the number of sporangia per sores, with the highest known count approaching 1000 sporangia per sorus. The Alsophila‐Nephelea evolutionary line has probably not been ancestral in the phylogeny of the more advanced groups of ferns.