Genus 2. 



WATER-PLANTAIN FAMILY. 



95 



2. HELIANTHIUM Engelm. ; Britton, Man. Ed. 2, 54. 1905. 



Annual or perennial scapose marsh or aquatic herbs. Leaves erect or ascending, or 

 floating, narrow and gradually narrowed into the petiole or broad and deeply cordate at the 

 base, 3-several-ribbed. Scapes as long as the leaves or longer, terminating in a few-flowered 

 whorl or a many-flowered panicle, the pedicels spreading or recurving in fruit. Flowers per- 

 fect. Sepals 3, broad, embracing the fruit-head or reflexed beneath it. Petals 3, mainly 

 white or pink, about as long as the sepals. Stamens 6 or 9 ; filaments elongate ; anthers very 

 short, often broader than long. Carpels relatively few, borne in few series on an elevated 

 receptacle. Style not apical, minute;. stigma acute. Achenes forming a globular or depressed 

 head, turgid, crested-ribbed, obscurely beaked or beakless. [Name from the Greek, meaning 

 sunflower.] 



Two known species, the following, and one in Cuba. Type species : Echinodorus parvulus 

 Engelm. 



Helianthium parvulum (Engelm.) Small. Dwarf Water-plantain. Fig. 224. 



?Alisma tenellum Mart. ; R. & S. Syst. Veg. 7 : 



1600. 1830. 

 Echinodorus parvulus Engelm. in A. Gray, 



Man. Ed. 2, 438. 1856. 

 ^Echinodorus tenellus Buchenau, Abh. . Nat. 



Gesell. Bremen 2: 18. 1868. 

 Helianthium tenellum Britton, Man. Ed. 2, 54. 



1904. 

 Helianthium parvulum Small, N. A. Fl. 17 1 : 



45. 1909. 



Plants 6' tall or less; leaves linear to 

 elliptic or oblong, 4"-i5" long, acute or 

 acutish at the apex, 3-veined, gradually nar- 

 rowed into the slender petioles which usually 

 somewhat exceed the blade in length ; scapes 

 solitary or few together, mostly as long as 

 the leaves or longer; pedicels' mostly 2-8, 

 recurved in fruit, ii"-2^" long; sepals or- 

 bicular-ovate or deltoid-ovate, l"-2" long; 

 petals suborbicular, about as long as the 

 sepals, emarginate at the apex ; fruit-heads 

 globular, iV -2" in diameter, embraced by 

 the persistent calyx ; achenes 4"-i" long, the 

 ribs obscurely crested. 



In mud and shallow water, Massachusetts 

 to Western Ontario, Minnesota, Florida, Texas 

 and Mexico. Also in Cuba. April-Aug. This 

 species was referred in the first edition of 

 this work to Alisma tenellum Mart, a plant 

 similar in habit, which appears to be con- 

 fined to South America ; it has been re- 

 garded by other authors as an Echinodorus. 



3. ECHINODORUS Rich. ; Engelm. in A. Gray, Man. 460. 1848. 



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

 or sagittate leaves, 3-9-ribbed and mostly punctate 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, per- 

 sistent; petals white, deciduous; receptacle large, convex or globose; stamens 12-30; ovaries 

 numerous; style obliquely apical, persistent; stigma simple; fruit achenes, more or less com- 

 pressed, 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 following are known in North 

 America. Type species : Alisma rostratum Nutt. 



Scapes reclining or prostrate ; style shorter than the ovary ; beak of achene short. 1. E. radicans. 



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



