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.
Salviniaceae.
The two genera of Salviniaceae, Salvinia and Azolla, are water plants, and are usually described as annuals which survive the less favourable season in the form of detached sporocarps. Goebel[1211] states that all the tropical species of Salvinia known to him have an unlimited existence.
Salvinia natans, Hoffm., the only European species, extends from the South of France to Northern China and the plains of India: the other twelve species are mostly tropical. Azolla, represented by four species, occurs in Western and Southern North America, South America, Madagascar, Australia, New Zealand, and is widely spread in tropical Asia and Africa.
Species of Azolla frequently form a considerable proportion of the floating carpet of vegetation on inland waters[1212] growing under conditions which might be supposed favourable for preservation in a fossil state.
The Salviniaceae, though probably rather farther removed than the Marsiliaceae from the homosporous Filicineae, are considered by Bower[1213] to be related to the Gradatae, but modified in consequence of their aquatic habit and the assumption of heterospory.
No undoubted examples of fossil species of Azolla have been described. Salvinia, on the other hand, is represented by several Tertiary species, for the most part founded on leaves only, and Hollick[1214], who published a list of fossil Salvinias, has described detached leaves as Salvinia elliptica Newb. from what may be Upper Cretaceous rocks from Carbonado, Washington. Some of the leaves figured as Tertiary Salvinias are of no value as evidence of the former distribution of the genus[1215].
From the Coal-beds of Yen-Bäi (Tonkin), probably of Miocene age, Zeiller[1216] has figured some well-preserved impressions of oval or orbicular leaves, 15 mm. long and 10–20 mm. broad, characterised by reticulate venation and by cordate bases, which he refers to Heer’s Swiss species Salvinia formosa[1217].
Dr Zeiller[1218] in the most recently published part of his series of valuable résumés of palaeobotanical literature refers to a description by Brabenec of specimens of this species from Bohemian Tertiary beds showing both microspores and megaspores.