Family 1. PODOSTEMONACEAE 



By GEORGK VAI.ENTINE NASH 



Immersed aquatic annual or perennial herbs, usually strongly adhering to 

 rocks and creeping upon them, with branching or disc-like rhizomes and usu- 

 ally fleshy stems ; leaves of various form, ranging from flat and fucus-like and 



more or less lobed to decompound, and flowers variously disposed. Flowers 

 perfect, naked or at first enclosed in a spathe which is later disrupted by 

 the elongating pedicel and remains at its base. Perianth wanting, or reduced 

 to a few minute scales, of large and membranous and 3-toothed or 5-parted. 

 Stamens hypogynous, 1-many, when many the filaments free in complete or 

 incomplete whorls, or more or less united at the base ; anthers of two parallel 

 cells. Ovary sessile or stipitate, free, usually 2-3-celled. Styles 1-3, distinct, 

 or shortly connate at the base, linear to leaf-like. Ovules numerous, attached 

 to central or parietal placentae. Capsule 2-3-celled, dehiscing septicidally, or 

 sometimes 1-celled, the valves usually with evident nerves, two, equal or un- 



F 



equal, or three and equal. Seeds numerous, sessile ; endosperm wanting. 



Flowers with perianth ; stamen 1 ; spathe wanting. 1. Tristicha. 



Flowers without perianth or perianth rudimentary ; spathe present. 

 Valves of the capsule equal ; stamens free. 



Stamens usually many, in a complete whorl. 2. Marathrum, 



Stamens usually few, in an incomplete whorl. 3. Blandowia, 



Valves of the capsule unequal. 

 Stamens 2, united below. 

 Stamen 1. 



4. PODOSTEMON 



5. OSERYA. 



1. TRISTICHA Thouars (Nov. Gen. Madag. 3. 1806, hyponym) ; 



Spreng. Syst. Veg. 1 : 22. 1825. 



Dufourea Bory ; Willd. Sp. PI. 5 : ^$. 1810. Not Dufourea Ach. 1810. 

 Philocrena Bong. Mem. Acad. St. Petersb. VI. 1 : 80. pi. 6. 1832, , 



Potamohryon I,iebm. Forh. Skand. Nat. Kiob. 1849 : 512. 1849. 



Moss-like submersed aquatic herbs, with short and densely tufted or elongated much- 

 branched stems, small sessile crowded 3-ranked leaves, and flowers usually in pairs at the 

 ends of the short branches. Perianth thin-membranous, 3-lobed,-the lobes slightly imbri- 

 cated. Stamen 1 ; filament filiform. Ovary 3-celled ; placenta central. Styles 3, linear^ 

 short, erect. Capsule septicidally 3-valved, the valves 3-nerved, equal. 



Type species, Tfisticha alternifolia Thouars. 



1. Tristicha hypnoides (St. Hil.) Spreng. Syst. Veg. 4': 10. 1827. 



Dufourea hypnoides St. Hil. Mem. Mus. Paris 10 : 472, 1823. 

 Potatnobryon concinnum L,iebm. Forh. Skand. Nat. Kiob. 1849 : 513. 1849. 

 Potamobryon laxum Iviebm. Forh. Skand. Nat. Kiob. 1849 : 514. 1849. 

 Potamobryon patulum I^iebm. Forh. Skand. Nat. Kiob. 1849 : 515. 1849. 



A tufted or creeping leafy-stemmed branching aquatic. Stems usually less than 1 dm. 

 long, commonly but 2-3 cm.; leaves from elliptic to broadly ovate, obtuse, entire, generally 

 tristichously arranged, usually crowded, 0.75-2 mm. long; pedicel 3-15 mm. long; perianth*- 

 parts oblong-elliptic ; capsule ellipsoid, about 1 mm. long. 



Type locality : Brazil. 



Distribution : Vera Cruz and Guatemala to Colombia, Guiana, Brazil and Cuba. 

 Illustrations : Arch. Mus. Hist. Nat. 6 : pi. 10, f. 4 ; Mart. Fl. Bras. 4^: pi. 75,/. 5 ; Vidensk. 

 Selsk. Skr. VI. Nat. og Mat. 9 : 108-113,/. 1-6, and 11 : 25-28,/. 20-23. 



Volume 22, Part 1, 1905] 3 



