500 COMPOSITAE, ou Ti. 
1. Megalodonta Béckii (Torr.) Greene. 
Water Marigold. Fig. 4518. 
Bidens Beckii Torr.; Spreng. Neue Entdeck. 2: 
Wah. 1821; 
M. Beckii Greene, Pittonia 4: 271. 1901. 
M. nudata Greene, loc. cit. 1901. 
Stems simple, or little branched, 2°-8° long. 
Submersed leaves sessile, 1’-2’ long, repeat- 
edly divided into numerous capillary segments; 
emersed leaves few, sessile, opposite, or some- 
times in 3's, lanceolate or oblong, acute, serrate 
or laciniate, 4’-14’ long; heads solitary or few, 
short-peduncled, 1’-13’ broad; involucre hemi- 
spheric, its bracts oval or oblong, obtusish, 
glabrous, the outer somewhat shorter than the 
inner; rays 6-10, obovate, or oblong, notched, 
golden yellow; achenes nearly terete, 5’—7” 
long; pappus of 3-6 slender awns, downwardly 
partes above, smooth below, divergent, 6-12” 
ong. 
In ponds and streams, Quebec to New Jersey, 
west to Manitoba and Missouri. Aug.—Sept. 
73. THELESPERMA Less. Linnaea 6: 511. 1831. 
Glabrous annual or perennial herbs, with opposite linear and undivided, or finely dis- 
sected leaves, and long-peduncled heads of both tubular and radiate flowers, or the rays 
wanting. Involucre hemispheric or campanulate, of 2 distinct series of bracts, the outer 
short, narrow and somewhat spreading, the inner united nearly to or beyond the middle into 
a cup, their tips scarious-margined. Receptacle flat, chaffy, the 2-nerved broad.white scarious 
chaff subtending the disk-flowers and achenes. Ray-flowers, when present, neutral, the rays 
yellow, entire or toothed. Disk-flowers perfect, fertile, their corolla with a slender tube and 
5-toothed limb. Anthers obtuse and entire at the base. Style-tips acute. Achenes, some or 
all of them, papillose on the back, oblong or linear, slightly compressed or terete, wingless. 
Pappus of 2 retrorsely hispid awns or scales, or sometimes none. [Greek, nipple-seed.] 
About ro species, natives of the south central United States, Mexico and southern South Amer 
ica. Type species: Thelesperma scabiousoides Less. 
Rays large; pappus-awns shorter than the width of the achene. 
Leaves not rigid, their segments filiform-linear; annual or biennial. 1. T. trifidum. | 
Leaves rigid, their segments linear; perennial. . 2. T. intermedium. 
Rays inconspicuous, or none; awns longer than the width of the achene; perennial. ; 
3. T. gracile. 
1. Thelesperma trifidum (Poir.) Brit- 
ton. Fine-leaved Thelesperma. an 
Fig. 4519. ‘SK 
Coreopsis trifida Poir. in Lam. Encycl. Suppl. 2: 
353. FBi ts : 
Thelesperma filifolium A. Gray, Kew. Journ. Bot. 
I: 252. 1849. 
Thelesperma trifidum Britton, Trans. N. Y. Acad. 
Sci. g: 182. 1890. 
Annual or biennial; stem branched, 1°-3° 
high. Leaves numerous, not rigid, 14’-2’ long, 
bipinnately divided into filiform or linear- 
filiform segments; heads several or numerous, 
12”-15” broad; outer bracts of the involucre 
about 8, subulate-linear, equalling or more 
than half as long as the inner, which are 
united not higher than the middle; rays 6-10, 
somewhat spatulate, 3-lobed; disk purple or 
brown; achenes linear-oblong, straight, or 
slightly curved, the outer ones strongly papil- 
lose; awns of the pappus not longer than the 
width of the summit of the achene. 
In dry soil, South Dakota, Missouri and Ne- 
braska to Colorado, Texas, New Mexico and north- 
ern Mexico. June-Aug. 
