Ceratophyllum. CERATOPHYLLACEiE. 169 



Group 5. Floicers either i)erfect or diclinous, hracteate or involucrate, commonly 

 destitute of both calyx and corolla. Ovary simple, or of 2 — 4. combined carpels. 

 — Submej'sed or gating herbs. 



Order XCIII. CERATOPHYLLACE^. S.F.Gray. The Hornwort Tribe. 



Flowers monoecious. Calyx and corolla none. Involucre 8 - 12-cleft. Sterile 

 FL. Stamens 12 - 24, without filaments : anthers 2-celled. Fertile fl. Ovary 

 simple, one-celled, with a solitary pendulous ovule : style filiform, oblique : 

 stigma simple. Fruit a beaked achenium. Seed with four cotyledons and a 

 conspicuous plumule. — Floating herbs, with whorled leaves cut into numerous 

 filiform segments. Flowers small and sessile, in the axils of the leaves. 



1. CERATOPHYLLUM. Linn.; Endl. gen. 1829; A. Gray in ann. lye. New-York, 4. 



p. 41. HORNWORT. 



[ From the Greek, kcras, a horn, and phyllon, a leaf: so named on account of the forked leaves.] 



Character same as of the order. 



1. Ceratophyllum echinatum, A. Gray. Rough-fruited Hornwort. 



Achenium elliptical, slightly compressed, with 3 short spines, the sides strongly muricated ; 

 margins slightly winged, not gibbous, armed with blunt teeth, which finally become weak 

 spines or horns as long as the lateral spines (7^. (|- Gr.). — A. Gray, I. c. ; Torr. ^ Gr. fl. 

 N. Am. 1. p. 56. C. demersum (wholly or in part) of American botanists. 



Whole plant submersed, of a dark green color. Stem branching, filiform, jointed. Leaves 

 in numerous whorls of G - 8, sessile, half an inch or an inch long, cut in a dichotomous or 

 trichotomous manner ; the segments serrulate, and mostly with 2 sharp teeth at the summit. 

 Flowers minute, solitary, with a many-cleft involucre at the base, which is often described as 

 a calyx. Anthers sessile, crowded in the centre of the involucre, 3-pointed at the summit. 

 Achenium on a short stipe, oblong. 



Ponds and slow-flowing streams. Fl. June - July. Fr. August. 



[Floka— Vol. 2.] 22 



