ALISMACE^E. ( WATER-PLANTAIN FAMILY.) 447 



impressed-nerved, longer than the filiform petioles ; immersed leaves filiform, 

 scattered ; spikes oval or oblong, short-peduncled ; achenium nearly circular, 

 concave on the sides, rugose or tubcrculate, and 1 - 3-ridged on the back ; 

 embryo coiled. (P. setaceus, Pursh. P. heterophyllus, Ell. ?) Shallow ponds, 

 Florida, and northward. June -Aug. Floating leaves 6" -8" long, com- 

 monly 5-nerved. 



ORDER 139. ALJSMACE^E. (WATER-PLANTAIN FAMILY.) 



Marsh herbs, usually with creeping runners or rootstocks, nerved and 

 reticulated sheathing leaves, and scape-like stems, bearing the perfect or 

 monoecious flowers in spikes or whorled racemes. Sepals and petals 3, 

 or the latter sometimes wanting. Stamens few or numerous : anthers 2- 

 celled. Ovaries 3 or many, with 1-2 anatropous or campylotropous erect 

 ovules. Style short or none. Achenium coriaceous, 1 - 2-seeded. Em- 

 bryo straight or curved, without albumen. 



Synopsis. 



SUBORDER I. JUNCAGINEJE. Sepals and petals (when present) 

 greenish. Ovule anatropous. Embryo straight. 



1. TRIGLOCHIN. Leaves rush-like. Flowers in spiked racemes. 



SUBORDER II. ALISME^E. Petals white, deciduous. Ovule cam- 

 pylotropous. Embryo curved or hooked. 



2. AL1SMA. Flowers perfect. Achenia whorled. Racemes compound. 



3. ECHINODORUS. Flowers perfect. Achenia clustered in a head. 



4. SAGITTABIA. Flowers monoscious. Achenia clustered in a head. 



1. TRIGLOCHIN, L. 



Flowers 'perfect, in a spiked raceme.- Sepals 3. Petals 3, and greenish, like 

 the sepals, or none. Anthers 3-6, nearly sessile, oval. Ovaries 3-6, united 

 around a central axis, from which they separate at maturity, 1-ovuled. Stigmas 

 plumose. Embryo straight. Leaves rush-like, fleshy, 2-ranked. Flowers 

 small, bractless. 



1. T. triandrum, Michx. Leaves erect, linear-subulate, semi-terete, di- 

 lated at the base and sheathing the base of the terete scape ; flowers very numer- 

 ous, on short pedicels ; sepals oval, deciduous ; petals none ; anthers and ovaries 

 3; fruit globose-triangular, pointless, when dry 3-winged by the compressed 

 3-ribbed achenia ; embryo oblong. Salt marshes along the coast, West Florida 

 to North Carolina. Aug. - Sept. Scape and leaves - 1 high. 



2. ALISMA, L. WATER-PLANTAIN. 



Flowers perfect in a whorled panicle. Sepals 3. Petals 3, involute in the 

 bud, deciduous. Stamens 6 -12. Ovaries numerous in a simple whorl. Style 



