Onosmodium 



Kenneth Kent Mackenzie 



The genus Onosmodium, founded in 1803 by Michaux, is a 

 genus o{ Boraginaceae exclusively confined to North America and 

 very largely to that portion of the United States east of the Rocky 

 Mountains. The species are closely related and their proper iden- 

 tification has given much trouble to collectors, as evidenced by the 

 large number of incorrectly labeled specimens found in herbaria. 

 Many of the characters given in the standard manuals are not con- 

 stant, and are misleading unless used with considerable discrimina- 

 tion ; this probably accounts for the great number of errors in 

 herbarium determinations. The following notes are based on an 

 examination of the specimens contained in the herbaria of the 

 Missouri Botanical Garden, the New York Botanical Garden, and 

 Columbia University, and in the author's private herbarium. 



Properly limited, the genus is a very natural one and may be 



characterized as follows: 



Erect, rough-hairy, branching, very leafy perennials, with alter- 

 nate, entire, strongly veined leaves, and numerous flowers in ter- 

 minal, leafy-bracted, scorpioid racemes. Flowers whitish, green- 

 ish-white or yellowish, from sessile to short-pedicelled, the pedicels 

 usually somewhat elongating in fruit Calyx shorter than the 

 corolla, deeply 5-parted. Corolla tubular, slightly enlarged at 

 the throat, 5-lobed, glabrous within, more or less hairy outside, 

 the lobes erect, acute or acuminate, the sinuses somewhat inflexed. 

 Stamens five, inserted on the corolla, included; filaments minute ; 

 anthers glabrous, narrowly arrow-shaped, acutish, the apex just 

 about level with the sinuses of the corolla. Ovary four-parted. 

 Style filiform, exserted, long persistent. Nutlets 4 mm. long or 

 .less, usually but one or two maturing, globular to ovoid, smooth 

 or sometimes • sparingly pitted, white to dingy whitish-brown, in 

 some species noticeably constricted below, attached at base to the 

 nearly flat receptacle, the scar oi attachment about 2 mm. wide. 

 (Greek, '*like O^iosnia,'' an old-world genus of Boraginaceae^ 

 Seven species, confined to the United States and Canada. 



495 



