384 PODOSTEMACE^E. (RIVER-WEED FAMILY.) 



ORDER 100. CALLITRICHACE^E. (WATER-STAR WORTS.) 



Aquatic small annuals, with opposite entire leaves, and solitary polyga.- 

 mous flowers in their axils, without any proper floral envelopes, and with a 4- 

 lobed and 4-celled 4-seeded fruit ; consisting only of the genus 



1. CALLiTRlCHE, L. WATER-STARWORT. 



Stamen solitary, in the sterile flowers between a pair of bracts ; in the fertile, 

 placed between the pistil and the stem, and rarely also one on the outer side : 

 filament thread-like : anther heart-shaped, by confluence becoming 1-celled. 

 Fruit indehiscent, nut-like, 4-lobed and 4-cellcd; but the styles only 2, awl- 

 sbaped and distinct. Seed solitary and suspended, filling each cell, anatropous : 

 embryo slender, in the axis and nearly the length of the albumen. Foliage 

 very variable according to circumstances, as in most water-plants. (Name from 

 xaXos, beautiful, and 6pi, hair, from the almost capillary and usually tufted 

 stems.) 



1. C. venia, L. Fruit sessile or nearly so, with a pair of bracts at its 

 base ; lobes of the fruit keeled or slightly winged on the back ; floating leaves 

 ohovate or spatulate and narrowed into a petiole, the immersed ones linear, 

 rarely all linear or all spatulate-obovate. Shallow water ; very common. 

 April -Aug. (Eu.) 



Var. platycarpa (C. platycarpa, Kiltzing), has the fruit twice as large 

 and more wing-margined. (Var. TERRESTRIS is a state growing along the 

 margin of pools or brooks, procumbent, tufted, and small-leaved.) (Eu.) 



2. C. pcdllllClllata, DC. Fruit raised on a (sometimes short) mostly 

 long and slender peduncle, without bracts ; fruit regularly 4-lobed, the lobes bluntly 

 keeled. Rare: only observed southwestward. (Eu.) 



3. C. ailtUllllliUis, L. Fruit nearly sessile, without bracts; lobes of the 

 fruit (often irregular) sharply keeled on the back ; leaves linear or spatulate. 

 Not common. (Eu.) 



Var. liiiearis (C. linearis, Pursh) has the leaves all or chiefly narrowly 

 linear, and the lobes of the fruit not keeled. Common northward. 



ORDER 101. PODOSTEMACE^E. (RIVER-WEED FAMILY.) 



Aquatics, growing on stones in running water, with much the aspect of Sea- 

 weeds or Mosses ; the minute naked flowers bursting from a spathe-like invo- 

 lucre as in Liverworts, producing a 2-3-celled many-seeded ribbed pod; 

 represented in North America by the genus 



1. PODOST^MON, Michx. RIVER-WEED. 



Flower solitary, pedicelled, from a tubular sac-like involucre, destitute of 

 floral envelopes. Stamens borne on one side of the stalk of the ovary, with 

 their long filaments united into one for more than half their length, and 2 short 

 sterile filaments, one on each side: anthers 2-ccllcd. Stigmas 2, awl-shaped- 



