Marsiliaceae.
This family is usually spoken of as including the two genera Marsilia and Pilularia. Lindman[1202] has however founded a third genus, Regnellidium, on a Brazilian plant which is distinguished by some well-defined characters from all species of Marsilia. The members of the Marsiliaceae live for the most part in swampy situations. Marsilia is represented in Europe by M. quadrifoliata L. which occurs in Portugal, France, Germany and other parts of the Continent, extending also to Kashmir, Northern China, and Japan. Of the other 53 species, 17 are recorded from different regions in Africa, while others occur in South America, Asia[1203], Australia, and elsewhere.
Pilularia globulifera L. is the only British representative of the Hydropterideae. The remaining four species of the genus occur in South America, California, New Zealand, Australia, and P. minuta Dur. is met with in the South of France, Algeria, and Asia Minor in subtropical or warm temperate regions.
The Marsiliaceae are regarded as more nearly related to the Schizaeaceae than to any other family of homosporous ferns[1204]. Their heterospory, the production of sporangia in closed fruit-like sporocarps, and the anatomical features associated with existence in marshy habitats, tend to obscure the resemblances to the true ferns.
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The genus Marsilidium proposed by Schenk[1205] for a piece of an axis, bearing apparently a whorl of six leaflets, from the Wealden of Osterwald, cannot be regarded as satisfactory evidence of the existence of the Marsiliaceae in the Wealden flora of North Germany.
The six leaflets of Marsilidium speciosum, having a length of 5 cm., are similar in shape to the four leaflets of recent species of Marsilia, but they differ in the repeated dichotomy of the veins from the reticulate venation of the recent forms. It is worthy of note, however, that in Lindman’s Brazilian type Regnellidium diphyllum ([fig. 326], A), the leaflets are characterised by dichotomous and not by anastomosing veins.
Hollick[1206] has described some impressions of imperfect orbicular leaves with a “finely flabellate obscurely reticulated(?) venation” from Cretaceous rocks of Long Island as Marsilia Andersoni, but these are too fragmentary to be accorded this generic designation. My friend Dr Krasser informs me that he is describing some well-preserved leaves from Cretaceous beds of Grünbach in Lower Austria as Marsilia Nathorsti[1207]. He compares these with the recent form Marsilia elata, a variety of M. Drummondi.
Another Lower Cretaceous species Marsilia perucensis has been figured by Frič and Bayer[1208] as a stalked fruit-like body from Bohemia. This was originally described by Velenovský as M. cretacea, but under this name Heer[1209] had previously recorded a supposed sporocarp from Greenland. These fossils have little claim to recognition as examples of Marsiliaceous plants.
The fragment figured by Heer[1210] from Tertiary rocks of Oeningen as Pilularia pedunculata is too small to determine with reasonable accuracy. Other supposed representatives of the family mentioned in palaeobotanical literature are not of sufficient importance to describe.