4 FIELD MUSEUM OF NATURAL HISTORY BOTANY, VOL. IV. 



Xanihium oligacanthum Piper, a far-western species described from 

 Washington, appears from its description to be nearest this species. 

 But X. oligacanthum is described as having the fruiting involucres 

 5-7 mm. thick, not only 3.5-5 mm. thick as in our species. 



Xanthium arcuatum Millspaugh & Sherff sp. nov. PI. II, & V ff. 2 & 6. 



Herba annua, caule inermi, habitu X. leptocarpo non dissimilis; 

 foliis infra minute et subobscure reticulatis et resina punctatis. Fructus 

 pauciores et crassiores, 2-4 simul congregati, anguste ovati, apice rostris 

 et facie exteriore numerosis (100-170) aculeis armati; rostris rectis aut 

 minime arcuatis, apice hamosis, 3.5-5 mm. longis, non pubescentibus 

 sed infra puncta resinae ferentibus; aculeis tenuibus (subrectis aut) 

 maximam partem arcuatis, plus minusve rubro-purpureo tinctis, 4-6 

 mm. longis, apice hamosis, infra resiniferis ut corpus; corpore (rostris 

 non adjectis) demum 1.3-1.5 cm. longo et 5-6 mm. crasso. Achenia 2; 

 maiore circum 1.8 cm. longo et 5 mm. lato, 3-costato, levi, base obtuse 

 orbiculato, rostro abrupte aristato. 



T. F. Lucy, river shores and low places, Chemung County, New York, 

 October n, 1896 (type in Herb. Field Museum, cat. no. 4953). 



Not only are the burs more or less of a decidedly reddish-purple shade, 

 but the prickles are very numerous and are mainly flexed or arcuate 

 from the base to the apical hook, not straight as in X. americanum. 

 The burs suggest those of X. inflexum Mack. & Bush, but are smaller, 

 of more delicate structure and do not have strongly incurved beaks. 



Xanthium cylindricum Millspaugh & Sherff sp. nov. PI. Ill, & V ff . 3 & 7. 



Herba, veri similiter annua; caule inermi. Folia magna, alterna, 

 quibusdam foliis Hibisci militaris Cav. simillima, circumambitu sub- 

 deltoideo-ovata, trilobata (et fere hastata) aut quinquelobata, margine 

 dentata, basi triplinervia et cordata aut subtruncata, membranacea, 

 scabra aut tactui etiam fere levia, minute sed perspicue reticulata, 

 setulis adpressis vestita, infra paucis punctis resinae punctata, petiolis 

 adjectis 1.3-2.5 dm. longa, petiolis tenuibus et laminis subaequantibus. 

 Fructus multi, 3-8 simul congregati, cylindrico-fusiformi, rubro-badii, 

 rostris et aculeis armati, punctis minutis resinae punctati, aliter glabri; 

 duobus rostris arcuatis, ad apicem hamosis, 4-5 mm. longis; aculeis 

 (100-150) tenuibus, rubro-badiis, ad apicem hamosis, 2.5-3.5 mm - 

 longis; corpore (rostris non adjectis) 1.4-1.6 cm. longo, 4-5 mm. crasso. 

 Achenia 2; maiore circum 1.5 cm. longo et 3 mm. lato, 3-costato, levi, 

 base acute orbiculato, apice sensim in rostrum mucronulatum producto. 



J. K. Small and A.M. Huger, Chimney Rock to Hendersonville, North 

 Carolina, October 3, 1901 (type in Herb. Field Museum, cat. no. 401312). 



