HYDROCHARIDACE^E. (FROG's-BIT FAMILY.) 475 



ORDER 142. HYDROCHARIDACE^E. (FROG'S-BIT 



FAMILY.) 



Aquatic herbs, with monoecious or dioecious flowers, from a mem- 

 branaceous spathe. Sepals and petals 3, or the latter wanting, distinct 

 in the sterile flower, united into a tube in the fertile, and coherent 

 with the 1 - 9-celled ovary. Stamens 3 - 12. Ovules numerous, as- 

 cending, orthotropous. Stigmas 3-9. Fruit indehiscent, many- 

 seeded. Embryo straight, without albumen. 



Synopsis. 



* Ovary l-celled. Stigmas 3-5. 



1. ELODKA. Flowers polygamo-dioecious. Spathe sessile. Stamens 9. Leaves short, 



opposite or whorled. 



2. VALLISNERIA. Flowers dioecious. Spathe peduncled. Stamens 3. Leaves long, 



linear. 



3. HALOPHILA. Flowers dioecious, axillary. Leaves opposite. Marine herbs. 



* * Cells of the ovary and stigmas 6-9. 



4. LIMNOBIUM. Flowers monoecious. Stamens 6-9, monadelphous. Leaves cordate 



petioled. 



1. ELODEA, Michx. 



Flowers diceciously polygamous, enclosed in the bud in a 2-cleft axillary 

 sessile spathe. Sterile flowers minute. Sepals and petals 3. Anthers 9. 

 Fertile flowers pistillate or perfect. Sepals and petals united into a very 

 long and slender 6-parted tube. Stamens 3 - 6, perfect or sterile. Ovary 1- 

 celled, with three parietal placentae, few-ovuled. Style capillary, ad n ate to 

 the tube. Stigmas 3, each 2-lobed, exserted. Fruit oblong, coriaceous. 

 Perennial herbs, with elongated filiform branching immersed stems, and 

 small and very numerous opposite or whorled leaves. Fertilization effected 

 by the sterile flowers breaking away from the stem, and expanding at the sur- 

 face among the floating stigmas. 



1. E. Canadensis, Michx. Stem much branched; leaves 3-4 in a 

 whorl, sessile, varying from linear to elliptical, 1-nerved, pellucid and mi- 

 nutely serrulate. In slow-flowing streams and ponds. Cherokee, North 

 Carolina ( Curtis), and northward. July - August. Leaves 3" - 6" long. 



2. VALLISNERIA, Micheli. TAPE-GRASS. 



Flowers dioecious. Sterile flowers numerous, minute, crowded on a spadix, 

 which is enclosed in an ovate 3-leaved short-stalked spathe. Calyx 3-parted. 

 Corolla none. Stamens 3. Fertile flowers solitary, enclosed in a tubular 

 spathe, and borne on a very long and mostly spiral scape. Sepals and small 

 petals 3, united and coherent with the cylindrical l-celled many-ovuled ovary. 

 Stigmas 3, each 2-lobed. Seeds numerous, fixed to three parietal placentae. 

 Aquatic herbs, with creeping stems, and elongated strap-shaped leaves. 

 Fertilization effected mostly as in Elodea. 



