[Vol. 9 

 104 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



13, 1284, 1322, gen. no. 1184. 1791; Syst. Veg., ed. 13, 792, gen. 

 no. 1184. 1774; Sadebeck in Engl. & Prantl, Nat. Pflanzenfam. 

 I 4 : 756. 1901-02. 



Marsilea L. Fl. Suec. 996. 1745. 



Calamaria Dillen. Hist. Muse. 541. pi. 80. jig. 2. 1741 ; Kuntze, 

 Rev. Gen. PI. 2: 828. 1891-93; Post & Kuntze, Lexicon, 88. 

 1904. 



Subularia Ray, Syn. Meth. Stirp. Brit. 283. 1696. 



Cephaloceratodon Genn. Comment. Critt. Ital. [1] no. 2: 111. 

 1861. 



Isoetella Genn. Comment. Critt. Ital. [1] no. 2: 114. 1861. 



Perennials, submerged, amphibious, or terrestrial, with a 2-or 

 3-lobed, short fleshy axis or corm giving rise to numerous 

 branched roots and to a rosette of elongated, somewhat triangular 

 or quadrangular leaves. Leaves with 4 transversely septate, 

 longitudinal air-channels, with central fibre-vascular bundle; 

 peripheral groups of supporting cells present or absent, stomata 

 present or absent. Ligule a small, delicate, triangular exten- 

 sion of tissue on inner face of leaf above the sporangium. Spo- 

 rangium solitary, sessile, on adaxial side of leaf, contained within 

 a basal cavity, and more or less covered by a membranous tissue, 

 the velum, on the inner leaf face. Sporangia of two types, micro- 

 sporangia and megasporangia, bearing respectively microspores 

 and megaspores, which on germination) develop gametophytes, 

 the former with a single antheridium, the latter with archegonia. 

 Megaspores hemispherical at base, with equatorial ridge, and 

 three other crests joined at apex, with variously sculptured walls. 

 Microspores minute, powdery, usually oval. 



Type species /. lacustris L. Sp. PL 1100. 1753. 



KEY TO SECTIONS 



A. Surface of megaspores chiefly tuberculate or spiny. 



a. Megaspores tuberculate 1. Tuberculatae 



b. Megaspores spiny $2. Echinatae 



B. Surface of megaspores irregularly crested or reticulate. 



a. Megaspores irregularly crested 3. Cristatae 



b. Megaspores reticulate, at least on basal face ..__$4. Reticulatae 



SECT. 1. TUBERCULATAE 



1. TUBERCULATAE. Forms with 2 or 3-lobed corms; mega- 

 spores rarely smooth, usually marked with few or many large 

 warts or many small tubercles, chiefly simple. 



