656 



AMMIACEAE. 



VOL. II. 



47. SIUM [Tourn.] L. Sp. PI. 251. 1753. 



Perennial marsh herbs, with simply pinnate stem-leaves, the lower and basal ones often 

 pinnatisected, and compound large umbels of white flowers. Involucre and involucels of 

 numerous narrow bracts. Calyx-teeth minute. Petals inflexed at the apex. Stylopodium 

 depressed. Styles short. Fruit ovate or oval, somewhat compressed. Carpels with promi- 

 nent ribs ; oil-tubes 1-3 in the intervals. Seed-face flat. [Greek name of a marsh plant.] 



About 8 species, natives of the north temperate zone and South Africa. The following are the 

 only ones known to occur in the United States. Type species: Sium latifolium L. 

 Plant stout, 2-6 high; leaf-segments 7-17. i. S. cicutaefolium. 



Plant weak, i-3 high ; leaf-segments 3-7. 2. S. Carsoni. 



i. Slum cicutaefolium Schrank. 



Hemlock Water-Parsnip. 



Fig. 3171. 



Sium cicutaefolium Schrank, Bair. Fl. 1 : 558. 



1789. 



S. lineare Michx. Fl. Bor. Am. 1 : 167. 1803. 

 Sium latifolium of American authors, not of 



Linn. 



Erect, stout, branched, 2-6 high. Lower 

 leaves long-petioled, the uppermost nearly 

 sessile; petioles sheathing at the base; 

 leaf-segments 7-17, linear, or lanceolate, 

 ii'-S' long, ii"-i2" wide, acuminate at the 

 apex, sharply serrate, or the lowermost 

 pectinately dissected ; umbels 2' -3' broad, 

 8-2o-rayed; rays i'-ii' long; fruit ovate, 

 compressed, about li" long, the ribs promi- 

 nent. 



In swamps, Nova Scotia to British Colum- 

 bia, south to Florida, Louisiana and Califor- 

 nia. Very variable in leaf-form. July-Oct. 



2. Slum Carsoni Durand. Carson's 

 Water-Parsnip. Fig. 3172. 



Sium Carsoni Durand; A. Gray, Man. Ed. 5, 196. 

 1867. 



Stem slender, weak, i-2 long. Leaf-seg- 

 ments 3-7, those of the upper leaves linear, 

 or lanceolate, acute, or acuminate, i'-2' long, 

 ii"-3" wide, sharply serrate; lower leaves 

 often floating and very thin, the segments 

 broader and laciniate, or dissected ; umbels 

 i '-2' broad, 7-i5-rayed; rays 6"-i2" long in 

 fruit ; fruit somewhat smaller than that of the 

 preceding species. 



In streams, Maine, Massachusetts and Rhode 

 Island to Pennsylvania. Perhaps an aquatic race 

 of Sium cicutaefolium, but appearing distinct in 

 Pennsylvania. July-Aug. 



48. PTILIMNIUM Raf. Neog. 2. 1825. 

 [DISCOPLEURA DC. Mem. Omb. 38. 1829.] 



Annual erect glabrous branching herbs, with pinnately or ternately dissected leaves, and 

 compound umbels of white flowers. Bracts of the involucre several, filiform or dissected 

 in our species. Involucels present. Calyx-teeth obsolete. Petals obovate, the apex inflexed. 

 Stylopodium conic; fruit ovate, slightly compressed, glabrous. Carpels dorsally compressed, 

 the dorsal and intermediate ribs prominent, slender, the lateral ones very thick and corky ; 

 oil-tubes solitary in the intervals. Seed-face flat. [Greek, referring to the finely divided 

 leaves.] 



About 4 species. Besides the following, another occurs in Texas and one in the East Indies. 

 Type species: Ammi capillaceum Michx. 



Involucral bracts mostly pinnate; fruit i"-! 1 ^" long. i. P. capillaceum. 



Involucral bracts short, entire; fruit y 2 "-W' long. 2. P.Nuttallii. 



