CHAPTER XXIII 

 MARSILEACEAEi 



This Family comprises three genera of Ferns of semi-aquatic habit, 

 characterised by rather unusual modifications of the vegetative system, and 

 particularly by their heterospory. They are Marsilea, which is cosmopolitan, 

 with 56 species: Regnellidiuni from Brazil, with one species: and Pilularia 

 with 6 species, inhabiting Europe, America, and Australasia. These plants 

 have commonly been associated with the Salviniaceae under the heading of 

 the Hydropterideae, on the ground of their adaptation to aquatic life, and 

 the heterosporous character which they share with them. But such grounds 

 appear insufficient, since the similarities on which that assumed relation is 

 based may well have been of homoplastic origin. There are reasons, which 

 will appear as the description proceeds, for ranking the Marsileaceae apart 

 from the Salviniaceae, and relating them with the homosporous Schizaea- 

 ceae. They may be held as a series derivative from these, but modified in 

 accordance with a semi-aquatic habit. 



The sporophyte of Pilularia is a creeping rhizomatous plant, rooted in 

 mud, or even floating with pendent roots on the surface of water (Fig. 458). 

 From its rhizome spring leaves which are narrow and subulate with circinate 

 vernation (<^). Close to the base of each is a bud which repeats the characters 

 of the main shoot, and in fruiting specimens the spherical, short-stalked 

 sporocarp is attached on the adaxial side of the leaf-base. It resembles a 

 pill, hence the name of the plant. The extreme tip of the rhizome is curved 

 upwards: the leaves (/) arise alternately from its upper surface, and 

 associated with each are a bud (Jj) and a root (r): their relative positions 

 and sequence are shown in Figs. 458, b, c, d, and the probable conclusion 

 is that the buds are really dichotomous branches of the rhizome thrust 

 alternately aside, right and left (Vol. I, p, •/?>). Simple hairs {h) form 

 a protection for the young parts. Maisilea is similar in general habit, but 

 it differs in the form of the leaves. These may be floating when the plant 

 grows in water: but if on dry land they rise erect. Each of the aerial leaves 

 bears four equal pinnae at the end of a long stipe, giving the appearance 

 of a four-leaved Clover (Fig. 459). This state is best understood by com- 

 paring the juvenile leaves of which the earliest are simple and at first 

 subulate, as in Pilularia. Then successively there follow spathulate, then 



^ The name Marsilea dates from Linn. Gen. ed. i, 326 (1737). Many authors have since written 

 it Marsilia ; but following the accepted rules the correct form should be the original one, which is 

 accordingly adopted here. The name was derived from Count Luigi Ferdinand's Massigli (1656 — 

 1730)- 



