Revision of the North American Species of Heteroclad 



By G. N. Best 



(With Plates 13 and 14) 



HETEROCLADIUM Bryol. Eur. lasc. 49-51. 1852 



Somewhat large to rather small plants growing on stones, 

 rocks, rotten wood and the ground. Stems rigid, stoloniform, 

 sparingly radiculose and paraphyllose, complanately branched ; 

 leaves more or less papillose, margins plane and papillose-dentate, 

 costa short, thin, not rarely obsolete ; stem leaves triangular-ovate, 

 narrowly acuminate, cordate, subclasping ; branch leaves ovate to 

 ovate-lanceolate, acute, obtuse or acuminate ; pedicels smooth, 

 capsules inclined to horizontal, short-necked, annulate ; exostome 

 well developed ; endostomial band one third to one half the length 

 of the teeth with well-developed segments and cilia ; operculum 

 conic to rostrate ; calyptra cucullate, fugacious. 



The short, thin, usually broad costa and the elongated, cir- 

 cumscribed leaf-cells of the basal-central area separate the mem- 

 bers of this genus from the closely related Thuidia. The Pseu- 

 doleskeae y while more distinctly plants of high altitudes, in their 

 distribution closely approximate the range of the Heterocladia, 

 differing however from these in having their stem leaves plicate 

 with margins recurved and costae well developed. 



Key to Species 



Leaves smooth. 



Operculum conic. 



Ultimate branch leaves spreading. H. procurrens. 



I eaves more or less papillose. 



Ultimate branch leaves imbricate. H. squarromlum 



Operculum rostrate. 



Cells of branch leaves with 2 to 5 papillae. 

 Ultimate branch leaves acute or short acuminate. H. heteropterioide 



Cells of branch leaves with I to 3 papillae. 

 Ultimate branch leaves long to acuminate, secund. H. Macounii. 



* The material on which this revision is based was furnished chiefly by the New 

 York Botanical Garden, the Geological Survey of Canada and the Agricultural Depart 

 ment at Washington. My thanks are due those having these collections in charge and 

 also Mrs. Britton for invaluable assistance, Miss Alexandrina Taylor for the care with 

 which she has executed the drawings and M. Jules Cardot for notes and specimens 



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