54 FLORA. 



i. ALISMA L. 



Perennial or rarely annual herbs with erect or floating leaves, the blades several^ 

 ribbed, the ribs connected by transverse veinlets, or seemingly pinnately veined. 

 Scapes short or elongated. Inflorescence paniculate or umbellate-paniculate. 

 Flowers small, numerous on unequal 3-bracteolate pedicels, the petals white or 

 rose tinted. Stamens 6, subperigynous. Ovaries few or many, in one whorl on 

 the receptacle, ripening into flattened achenes which are 2-3-ribbed on the curved 

 back and l-2-ribbed on the sides. [Greek, said to be in reference to the occur- 

 rence of the typical species in saline situations.] About 10 species, widely dis- 

 tributed in temperate and tropical regions. 



x. Alisma Plantago-aquatica L. WATER PLANTAIN. (I. F. f. 188.) 

 Leaves ovate to linear, acute, cordate, rounded or narrowed at the base, the 

 blades 3-iO-ribbed; petioles 2-25 cm. long; scapes occasionally 2 from the same 

 root, usually solitary, 0.2-1.3 m. high; inflorescence a large loose panicle ; pedicels 

 verticillate in 3's-io's, subtended by 3 striate acuminate bracts; petals 1-2 mm. 

 long; styles deciduous, the base remaining as a small point or short beak on the 

 inner curve of the achene; stigma small, terminal; achenes obliquely obovate, 

 nearly 2 mm. long, arranged in a circle, forming an obtusely triangular truncate 

 head. In shallow water or mud throughout N. Am. Also in Europe and Asia. 

 lune-Sept. 



xa. HELIANTHIUM Engelm. 



A low perennial uliginous herb with narrow basal leaves and white flowers 

 umbelled at the summits of slender scapes. Sepals 3, ovate, obtuse; petals 3, 

 obovate, emarginate. Stamens 9, with thick filaments, 3 opposite each sepal ; 

 carpels several or. numerous, spirally arranged in a head; style very short; 

 carpels turgid, glandless, beakless. A monotypic genus. 



i. Helianthium tenellum (Mart.) Britton. DWARF WATER PLANTAIN. 

 Plant delicate, stoloniferous, 2-12 cm. high. Leaves lanceolate or linear-lanceo- 

 late, the blades acute at both ends, 6-30 mm. long, 2-6 mm. wide ; petioles 

 longer or shorter than the blades, narrowly dilated at the base ; scape solitary, 

 often surpassing the leaves, commonly reclined ; umbel 2-8-flowered ; pedkels 

 very unequal, often recurved in fruit; bracts lanceolate, more or less connate at 

 the base. In mud, Mass, to W. Ont. and Minn., south to Fla., Mo., Tex., Mex. 

 and in S. A. April- Aug. [Alisma tenellum Mart.; Echinodorus parvulus 

 Engelm.] 



2. ECHINODORUS Rich. 



Perennial or annual herbs with long-petioled elliptic, ovate or lanceolate, often 

 cordate or sagittate leaves, 3-9-ribbed and mostly punctuate with dots or lines. 

 Scapes often longer than the leaves; inflorescence racemose or paniculate, the 

 flowers verticillate, each verticil with 3 outer bracts and numerous inner bracteoles; 

 flowers perfect; sepals 3, distinct, persistent; petals white, deciduous; receptacle 

 large, convex or globose; stamens 12-30; ovaries numerous; style obliquely api- 

 cal, persistent; stigma simple; fruit achenes, more or less compressed, coriaceous, 

 ribbed and beaked, forming spinose heads. [Greek, in allusion to the spinose 

 heads of fruit.] About 14 species, mostly natives of America. Only the follow- 

 ing are known in N. Am. : 



Scapes reclining or prostrate; style shorter than the ovary; beak of achene short. 



i. E. radicans. 

 Scapes erect; style longer than the ovary; beak of achene long. 2. E. cordifolius, 



i. Echinodorus radicans (Nutt.) Engelm. CREEPING BUR-HEAD. (I. F, 

 f. 190.) Leaves coarse, ovate, obtuse, cordate, 5-20 cm. long, 3-18 cm. wide, marked 

 with short pellucid lines, the nerves 5-9, connected by netted cross-veins. Petioles 

 sometimes 0.5 in. long; scapes creeping, 0.6-1. 4m. long, slightly scabrous, often root- 

 ing at the nodes; verticils distant; pedicels 3-12, unequal, slender or filiform; sepals 

 persistent, much shorter than the heads; petals larger, obovate, about 6 mm. long; 

 stamens about ;o; style shorter than the ovary; achenes numerous, about 4 mm. 

 long, 6-io-ribbed, with 2-several oval glands on each side and beaks about one- 



