6 



NORTH AMERICAN FLORA 



[Volume 34 



panulate, about 1 cm. high; bracts obtuse, elliptic, or the outer oval and much shorter; ray- 

 flowers 10-15; achenes about 3 cm. long, somewhat angled; pappus-bristles tawny, about 5 mm. 

 long. — 



Type locality: Laredo, Texas. 

 Distribution: Southern Texas. 

 Illustration: Hook. Ic. pi. 1105. 



Excluded species 



Clappia aurantiaca Benth. in Hook. Ic. III. 2: 3. pi. 1104 (1876) is Clomenocoma aurantia 

 (L.) Cass. 



Jaumea tenuifolia Klatt, Leopoldina 23: 146. 1887. (Neurolaena tenuifolia Schultz- 

 Bip.; Klatt, Leopoldina 23: 146, as synonym. 1887.) This has capillary pappus and oblong 

 striate bracts, and is apparently rayless. It belongs probably to the Eupatorieae. 



Subtribe 2. RIDDELLIANAE. Heads radiate. Ray-flowers pistillate 

 and fertile, the disk-flowers hermaphrodite and fertile or in Wkitneya sterile. 

 Ligules becoming papery, persistent on the achenes, falling off with them. 

 Involucre of 1-2 series of nearly equal bracts. Receptacle alveolate. Achenes 

 many-striate. Plants more or less woolly, without oil-glands. 



Pappus paleaceous; ligules broad and few, mostly 3-5, rarely more; receptacle 



naked. 8. Psilostrophe. 



Pappus wanting; ligules usually numerous. 



Involucre hemispheric; receptacle naked; leaves alternate. 9. BailEya. 



Involucre campanulate; receptacle villous; leaves opposite. 10. Whitneya. 



8. PSILOSTROPHE DC. Prodr. 7: 261. 1838. 



Riddellia Nutt. Trans. Am. Phil. Soc. II. 7: 371. 1841. 



Perennial herbs or low shrubs, more or less tomentose or woolly. Leaves alternate, entire 

 or slightly lobed. Heads radiate, usually short-peduncled, corymbosely arranged. Involucre 

 cylindraceous, campanulate, or rarely turbinate, of a single series of equal, lanate, more or less 

 connivent bracts, and sometimes 1-4 scarious within and one small calyculate one below. 

 Receptacle small, naked. Ray -flowers pistillate, in a single series; ligules broad, 3-lobed, 4- 

 nerved, yellow, becoming papery in age and persistent on the achenes. Disk-flowers her- 

 maphrodite, fertile, regular; tube very short; throat cylindric; limb with 5 short, glandular 

 lobes. Anthers obtuse at the base, with lanceolate tips. Style-branches truncate-capitellate 

 at the apex. Achenes linear, obtusely angled, striate, either glabrous or nearly so, or long- 

 villous. Pappus of acute or obtuse, unequal, lacerate or ciliate squamellae. 



Type species, Psilostrophe gnaphalodes DC. 



Pubescence of the stem villous or villous-hirsute. 



Achenes long-villous. 1. P. gnaphalodes. 



Achenes glabrous or nearly so. 



Squamellae of the pappus lanceolate to subulate, acute. 

 Stem loosely white-villous. 



Ligules 3-4 mm. long. 2. P. villosa. 



Ligules 5-7 mm. long. 3. P. Tagetinae. 



Stem green, sparingly pilose and glandular-granuliferous. 



Branches long, as well as leaves strongly ascending. 4. P. sparsiflora. 



Branches short, more or less spreading; leaves divaricate. 5. P. divaricata. 



Squamellae ovate to lance-elliptic, obtuse. 



Shrub 3-6 dm. high; ligules about 3 mm. long. ■ 6. P. Harlmanii. 



Undershrubs 1-4 dm. high; ligules 6-12 mm. long. 



Plant about 3 dm. high; involucre 5-6 mm. high, 3-4 mm. 

 broad; squamellae lance-elliptic. 

 Plant green, short-villous; leaves entire; ligules 8-10 cm. long. 7. P. gr audi flora. 

 Plant grayish, densely long-villous; some of the lower stem- 

 leaves usually lobed; ligules 6-8 mm. long. 8. P. lanata. 

 Plant 1-2 dm. high; involucre 6-8 mm. high, 4-5 mm. broad; 



sqamellae ovate. 9. P. Bakeri. 



Pubescence of the stem densely white-pannose. 10. P. Cooperi. 



