148 DICOTYLEDONOUS PLANTS. 



1. A. rigida De Cand. : stem erect, rigid, striate ; leaves pinnate, 

 smooth ; leafets 4 5 pairs, large, oblong-lanceolate, entire or with 

 several remote teeth j umbels terminal, on long peduncles ; general 

 involucre none ; partial one of 68 subulate leaves ; fruit much com- 

 pressed. Sium rigidius Linn. Slum marginatum Mich. Pastinaca 

 rigida Spreng. Torr. (Enanthe rigida Nutt. 



HAB. Swamps. N. J. to S. Car. Sept. Lf. Stem 2 4 feet 

 high. Leaves with a white and sometimes scabrous margin. 

 Flowers white. 



2. A. ambigua De Cand. : stem erect, slightly angular ; leaves pin- 

 nate, smooth ; leafets narrow-linear or linear-lanceolate, long, mostly 

 entire, somewhat glaucous beneath ; umbels terminal, subsolitary ; 

 general involucre none ; partial one of 3 5 subulate leaves. 

 (Enanthe ambigua Nutt.Pastinaca ambigva Torr. Sium longifolium 

 Pursh. 



HAB. Brackish swamps. N. J. Aug. 2[.Stem 35 fee: 

 high. Floicrrs white. Dr. Torrey considers this plant identical 

 with (Enanthe ambitrna of Nuttall ; while according to the latter 

 botanist it is undoubtedly Sium lincare of Linneeus. The prin- 

 cipal difference between the present plant as characterized by 

 Torrey and S. lineare, consists in the absence of the general 

 involucre. Dr. Asa Gray informs me tliat this species has been 

 found in the sandy swamps of Michigan. 



18. PASTINACA. Linn. 



Calyx with the margin obsolete or minutely denticulate. 

 Petals roundish, entire, involute. Fruit dorsally and flatly 

 compressed, surrounded by a dilated margin. Carpels with 

 very slender ribs ; 3 intermediate ribs equidistant ; 2 lateral 

 ones contiguous. Umbels' compound. Involucres none or 

 few-leaved. Flowers yellow. Pentandria. Digynia. 



P. saliva Linn. : stem smooth, sulcate ; leaves pinnate ; leafets ses- 

 sile, subpubescent beneath, oblong, incised, terminal one 3-lobed ; um- 

 bels large, terminal ; fruit oval, much compressed. 



HAB. Fields. July, Aug. tf.Stcm 23 feet high. FUncer* 

 yellow. Introduced. Wild Parsnip* 



19. HERACLEUM. Linn. 



Calyx 5-toothed. Petals obovate, emarginate, inflexed ; 

 outer ones often rayed, bifid. Fruit dorsally and flatly com- 

 pressed, surrounded by a membranaceous margin. Carpels 

 with 3 equidistant ribs on the back; 2 lateral ribs with a di- 

 lated margin. Umbels many-rayed. General involucre ca- 

 ducous, often few-leaved ; partial one many-leaved. 



Pentandria. Digynia. 



