420 PODOSTEMACE^E. (RIVERWEED FAMILY.) 



ORDER 117. CALLITRICHACE^E. (WATER-STARWORT 



FAMILY.) 



Small aquatic annuals, with opposite entire leaves, and solitary ax- 

 illary polygamous flowers without floral envelopes. Stamen mostly 

 solitary, 2-bracted in the sterile flower. Filament slender: anther 

 reniform, the cells confluent Styles 2, slender: stigmas acute. Cap- 

 sule 4-angled, 4-celled, with a single suspended anatropous seed in each 

 cell, iiidehiscent. Embryo straight, in copious fleshy albumen. Rad- 

 icle long, superior. Consisting of the single genus 



1. CALLITBICHE, L. WATER-STARWORT. 



1. C. heterophylla, Pursh. Floating leaves spatulate or obovate, 

 crowded, the lower ones distant, linear ; fruit nearly sessile, 2-bracted, keeled 

 011 the back. Var. TERRESTKIS. Smaller (2' -3' long); stems much 

 branched, creeping on damp earth; leaves (l"-2" long) all linear. 

 Ditches and shallow water, Florida, and northward. March - April. Stems 

 several, 6'- 12' long. Leaves \' long. 



2. C. peploides, Nutt. Stems creeping ; leaves uniform, obovate or 

 spatulate; fruit nearly sessile, circular, notched at the apex, the sides gibbous, 

 grooved around the wingless margin, as long as the widely spreading stigmas. 

 Florida and westward, 011 damp earth. Feb. - March. 



3. C. Austinii, Engelm. Smaller (!' or less long) ; fruit short-pedicelled, 

 flattened, wider than long, notched at both ends, with narrow denticulate 

 wings, longer than the spreading stigmas. Tennessee (Dr. Gattinger), aiid 

 northward. April. 



ORDER 118. PODOSTEMACEJE. (RIVERWEED FAMILY.) 



Moss-like aquatic plants, with minute flowers, from a spathe-like in- 

 volucre, and destitute of floral envelopes. Stamens 5- 12 : anthers 

 2-celled. Capsule 2-3-celled, pointed by as many persistent styles. 

 Seeds numerous, on a thick central placenta, destitute of albumen. 



1. PODOSTEMON, Michx. RIVERWEED. 



Spathe 2-leaved. Flowers pedicelled. Filaments elongated, borne on one 

 side of the stalk of the ovary, united below, and bearing only a single anther. 

 Styles 2, simple. Capsule ribbed, 2-celled, 2-valved. Seeds imbricated. 

 Submerged aquatic plants, attached to rocks and pebbles by disk-like expan- 

 sions of the stem. Leaves 2-ranked, divided into filiform segments. 



1. P. ceratophyllum, Michx. Leaves rigid, sparingly divided, sheath- 

 ing at the base ; flowers solitary, on slender pedicels ; capsule oval, 8-ribbed. 

 Rocky places in rivers, Georgia, and northward. July. Plant olive-green, 

 1'- 4' long. 



