Sporangia form circular naked sori composed of a variable number of sporangia, usually not more than ten and frequently fewer, characterised by an obliquely horizontal and almost complete annulus (fig. 224, I). In some species of _Gleichenia_ (sect. _Eugleichenia_) the ultimate segments are very small and semicircular in form (fig. 226, C), in others (sect. _Mertensia_[686]) the segments are linear (fig. 226, D), and in many species the fronds are distinguished by the regular dichotomous branching (fig. 225), frequently showing an arrested rachis bud in the forks[687] protected by modified pinnules (fig. 226, D, E). In _Platyzoma_ the leaves are simple, reaching a length of 20–30 cm., and bear small revolute oval segments. [Illustration: Fig. 224. A. _Aneimia flexuosa._ B. _A. phyllitidis._ C. _Hymenophyllum dilatatum._ D, E, F, G. _Matonia pectinata_; _i_, indusium. H. _Thyrsopteris elegans._ I. _Gleichenia circinata._ (A, B, after Prantl; C, G, H, I, after Bower.)] [Illustration: FIG. 225. _Gleichenia dicarpa._ (⅓ nat. size.)] [Illustration: FIG. 226. A, B. _Gleichenites Rostafinskii_, Raciborski. C. _Gleichenia dicarpa._ (Nat. size.) D, E. _Gleichenia dichotoma._ (Reduced.) (A, B, after Raciborski; C, after Hooker; D, E, after Goebel.)] _Gleichenia_ is represented by several species in the tropics and extends to south temperate and Antarctic latitudes. The species _G. dichotoma_ (= _G. linearis_) is one of the more successful tropical ferns, while _G. moniliformis_ (by some authors recognised as a distinct genus, _Stromatopteris_) is peculiar to New Caledonia. The monotypic genus _Platyzoma_ is a xerophilous Australian fern. The Gleicheniaceae are unrepresented in existing north temperate floras. =Matonineae.= (_Matonia._)