S6 



UNITED STATES AND MEXICi\N BOUNDARY. 



smaller than those of the disk. The fertile ovaries, at least the one or two which make the 

 longer and subulate achenia^ begin to elongate soon after anthesis, and to project to twice or 

 thrice the lenerth of the involucre. The scales of the latter subtend the fertile flowers, but do 

 not inclose or embrace them. Palea? of the receptacle much smaller than the involucral scales, 

 linear, plane, forming a circle between the ray and the disk, one subtending each sterile flower. 

 Sterile style barely bidentate at the apiculate tip. The longer achenia, which usually persist 

 after the fall of the involucre, etc., are from 3 to 4^ lines long, (excluding the awns,) barely 

 half a line in thickness, slightly obcompressed, even, not at all margined, tipped with two 



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stout, diverging or sometimes recurved-spreading, smooth, rigid, inarticulated and persistent, 

 subulate awns, of 1^ to 3 lines in length. There is usually only one such achenium to each 

 capitulura. The others are shorter and thicker, and tuberculate-rugose inside, but otherwise 

 similar, or one of them barely 2 lines long, oblong, truncate at both ends, the apex bearing two 

 very short and divaricate or almost obsolete awns or horns. 



Parthenium inca]s:um, II. B. K. ; Gray^ PL Wright^ 1,^. 103, & 2, p. 85. P. ramosissimum, 

 DC. Prodr. 5, p. 532. From the Pecos to Cobre, etc.; Bigelow^ Wright^ Schott. On the Eio 

 Grande, below Mount Carmel; Parr?/. 



Parthenium argentatum (sp. nov.): fruticosum, pube brevi appressima sericeo-incanum ; 



foliis spathulato-lanceolatis oblongisve in petiolum longe attenuatis parce dentatis seu laciniatis 

 Bub-triplinerviis ; ramulis floridis elongatis nudis oligocephalis; involucri squamis obtusissimis ; 

 acheniis sericeis; pappo o paleis 2 membranaceis lanceolatis. — Near Escondido Creek, Texas, in 



rocky places, Sept. 1852; Br. Bigelow. — A well marked species, connecting the sections Argy- 

 rochaeta and Parthenichaeta; the leaves and branches whitened with a very fine and close silky- 

 silvery pubescence, which appears to be wholly or nearly persistent. Leaves one to two inches 

 long, including the tapering base and petiole, 2 to 5 lines wide, mostly acute, scarcely veined, 

 beset on each margin with from one to three salient teeth, or sharp lobes. Flowering branchlets 

 slender, 4 to 8 inches long, nearly leafless and peduncle-like, bearing 3 to 7 sub-sessile heads 

 (as large as those of P. incanum) in a cluster. Exterior scales of the involucre short, orbicular- 

 ovate; the inner orbicular, scarious-membranaceous. Palese of the pappus lanceolate or oblong- 

 lanceolate, rather narrower and less obtuse than in P. Hysterophorus, puberuleiit, the inner 



edge more or less adnate to the base of the broadly obovate and cucullate emarginate 1 

 Parthenium Hysterophohus, Linn. Texas, etc. ; common in low places. 

 Parthenice mollis, Gray^ PI. Wriglit^ 2,2>. 85. Near Santa Cruz, Sonora; Wright^ Thurher. 

 EuFHROSYNE AMRRosiiEFOLrA, Gvay^ PL Wright^ 1, j>. 102, dt 2,^. 85. Near Conde's Camp, New 



Mexico; Wright. Cook's Springs; Bigelow. 



IvA DEALBATA, Gray^ PL Wright^ 1, p. 104. Leon Springs; Bigelow. Lagunas de Patos, 

 Chihuahua; Thurher. 



b 



DICORIA, Torr. & Gray, in Emory, Pep., 1848, p. 143. 



Capitulum monoicum; floribus foemineis 2 in ambltu, masculis 8-12 in disco. Involucrura 

 patulum, duplex, exterius e phyllis 5 ovalibus herbaceis uniseriatis, interius e squamis 2 orbicu- 

 latis tenuiter scariosis planis mox accrescentibus, utraqueflorem foemineumfulcrante. Recepta- 

 culum parvura, planum, jialeis angustis lineari-spathulatis inter flores. FL Poem. Corolla 

 nulla : stylus alte bifidus, ramis linearibus glabris. PL masc. Corolla obconica, 5-dentata. 

 Antherse vix coalite, sed filamentis monadelphis. Stylus abortivus in synemate apice 5-dentato 



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