STANDLEY — TREES AND SHRUBS OF MEXICO 1621 



108. SENECIO L. Sp. PI. 866. 1753. 

 (Contributed by Dr. J. M. Greeninan.) 



References: Greenman, Monogr. Senecio, Part I, pp. 1-37. 1901; Bot. 

 Jahrb. Engler 32: 1-33. 1902; Ann. Mo. Bot. Card. 2: 573-676. pi. 'l7-20. 

 1915; op. cit. 3: 85-194. pi. 3-5. 1916; op. cit. 4: 15-36. pi. 4. 1917- op cit' 

 5: 37-107. pi. 4-6. 1918. 



Herbs, suffruticose plants, shrubs, or woody, scandent or climbing perennials, 

 or even arborescent plants; leaves alternate, very variable, pinnately or pal- 

 mately veined, entire to variously divided; heads heterogamous and radiate, or 

 discoid; involucre narrowly campanulate, usually subtended by calyculate 

 bracteoles; bracts of the involucre uniseriate, or by overlapping subbiseriate, 

 Variable in number but tending to approach a definite series of numbers, namely 

 5-8-13-21, etc.; ray flowers when present disposed in a single row, fertile, the 

 rays sometimes reduced; disk flowers perfect; corollas slenderly tubular to 

 abruptly ampliate above into a campanulate 5-toothed hmb, the teeth mostly 

 short; anthers obtuse or slightly sagittate at the base; style branches truncate, 

 rounded-obtuse, occasionally terminated by a penicillate tuft of hairs or by a 

 triangular, acute or acuminate, dorsally hirtellous appendage; achenes subterete, 

 usually ribbed, glabrous or hirtellous; pappus of numerous white slender setae. 



A large genus, widely distributed, but of little economic value. 



KEY TO THE SUBGENERA AND SECTIONS. 



Style branches truncate, rounded-obtuse, or occasionally terminated by a penicil- 

 late tuft of hairs. (Subgenus Eusenecio.) 

 Stems erect or ascending, not climbing. 



Stems not abruptly terminated by a foreshortening of the main axis; oil 

 tubes not richly developed in the corte.x. 

 Leaves pinnately veined. 



Stems more or less ligneous at the base; suffruticose plants. 



Involucre barely calyculate I. INC ANI. 



Involucre distinctly calyculate II. SUFFRUTICOSI. 



Shrubs or treelike plants III. FRUTICOSI. 



Leaves palmately veined IV. PALMATINERVII. 



Stems abruptly terminated by a foreshortening of the main axis, and bear- 

 ing at the ape.x two to several more or less pedunculate, compound, 

 corymbose c3-mes; oil tubes richly developed in the cortex. 



V. TERMINALES. 



Stems climbing . VI. STREPTOTHAMNI. 



Style branches terminated by a triangular, acute or acuminate, dorsally his- 

 pidulous appendage; stems prostrate or scandent. (Subgenus Pseu- 

 DOGYNOXis.) VII. CONVOLVULOIDEI. 



KEY TO THE SIECIES. 



I. INCANI. 

 A single species in Mexico 1. S. palmeri. 



II. SUFFRUTICOSL 

 Inflorescence several to many-headed. 

 Leaves bi-tri-pinnatisect, not auriculate. 



Stems conspicuously tufted-pubescent in the leaf axils; leaves 1.5 to 6 cm. 



broad - 2. S. lyoni. 



Stems not conspicuously tufted-pubescent in the leaf axils; leaves 1.5 cm. 

 or less broad 3. S. cedrosensis. 



