The sporangia, which are attached to a columnar receptacle or prolongation of a vein beyond the margin of the lamina, are characterised by an obliquely transverse annulus (fig. 224, C). A cup-like indusium surrounds the lower portion of the receptacle which is two-lipped in _Trichomanes_ and entire in _Hymenophyllum_ (fig. 270, C, D). These two filmy ferns have a wide distribution both in tropical and extra-tropical regions; they are represented in the British Isles by _Hymenophyllum tunbrigense_, _H. Wilsoni_, and _Trichomanes radicans_. [Illustration: FIG. 229. A. _Thyrsopteris elegans._ B. _Cyathea spinulosa._ C. _Davallia concinna._ D. _Dicksonia coniifolia._ E. _Alsophila excelsa._ F, G. _Dicksonia culcita._ (A, after Diels and Kunze; B, D, F, G, after Hooker; E, after Bower.)] =Cyatheaceae.= (_Cyathea_, _Hemitelia_, _Alsophila_, _Dicksonia_, _Thyrsopteris_.) The sporangia occur in indusiate or naked sori and have an obliquely vertical and incomplete annulus (fig. 229, E). In the great majority of cases the fronds are large and highly compound, but _Cyathea sinuata_ Hook, a rare Ceylon species, bears simple narrow linear leaves. This family includes, with few exceptions, all the tree ferns[694]. The sori of _Dicksonia_ are enclosed in a two-valved indusium (fig. 229, F. G); in the species represented in fig. 230 the fertile segments, which terminate in cup-like indusia, are characterised by the absence of a lamina and closely resemble those of _Thyrsopteris_ (fig. 229, A). In _Cyathea_ the indusium has the form of a cup which is at first closed and afterwards opens at the apex (fig. 229, B); in _Hemitelia_ the indusium is much reduced and in _Alsophila_ the sori are naked. _Thyrsopteris_ is characterised by the reduced fertile pinnules bearing stalked sori in deep cups (fig. 229, A). The appearance of this fern “is very remarkable, for the cup-shaped sori hang down from the fronds in masses, looking just like masses of millet seed[695].” The sporangia are described by Bower[696] as large and of rather peculiar form. As seen in fig. 224, H, the annulus is continuous; it forms a twisted loop of cells which vary in shape and in the thickness of the walls. The Cyatheaceae are for the most part tropical ferns with a wide geographical range, usually in moist regions; they are, however, able to flourish under widely different temperature conditions. In Tasmania, as Diels[697] points out, tree ferns may occasionally be seen laden with snow, and on the west coast of New Zealand they overhang the edge of a glacier[698]. The monotypic genus _Thyrsopteris_ is confined to Juan Fernandez. The Cyatheaceae no longer exist in Europe. [Illustration: FIG. 230. _Dicksonia Bertercana_ Hook. Fertile and sterile pinnae. (Nat. size. British Museum Herbarium.)] =Dennstaedtiinae.= (_Microlepia_, _Dennstaedtia_.)