ROBINSON. — ALOMIA, AGERATUM, AND OXYLOBUS. 439 



from Agcratum and Trichogonia solely on the absence of pappus, the 

 genus may well ha^e a composite — at least a double — origin. 

 Either a Trichogonia, on the loss of its plumose pappus-bristles (a 

 condition known to occur in T. mcnthaefoUa and T. salviaefolia Gardn.), 

 or an Agcratum, on the complete abortion of its often obsolescent scale- 

 pappus, would become as to technical characters an Alomia, and the 

 fact that the genus Alomia, as now circumscribed, contains species of a 

 wide range of habit, extending on the one hand from the original A. 

 agerafoides, with distinctly ageratoid habit, to A. dubia, on the other, 

 which except for the lack of pappus would certainly be placed in 

 Trichogonia, it appears by no means unlikely that the elements now 

 grouped in Alomia ma^' have come in part from an ageratoid and in 

 part from a Trichogonia-like ancestry. 



Although from these considerations Alomia may seem an artificial 

 group, its components certainly have close affinity and our present 

 knowledge does not permit any improvement of the situation either 

 by dividing the genus on trifling traits of habit or by merging it bodily 

 with any of the neighboring genera. 



The three species here grouped as a new subgenus, Geissanthodium, 

 possessing softer much imbricated involucral scales (striate in the 

 manner of Brickellia), form an interesting strain, a small presumably 

 natural group. After careful comparison of A. alata Hemsl. and 

 Ageratum callosum Wats, it is impossible to see any grounds for their 

 generic separation. Either Ageratum callosum must be referred to 

 Alomia or the genus Alomia must be transferred to Ageratum. The 

 close relationship of the third species of this subgenus, the South 

 American A. Regnellii Malme, although less convincing, seems highly 

 probable to judge from Malme's description and figures. Some spe- 

 cious arguments might be advanced for the separation of these three 

 species as a new genus, but their distinctions from other species of 

 Alomia are not strong. Involucral characters in nearly related genera 

 are seen to be highly inconsistent and it is to be noticed that the im- 

 brication of the scales is by no means so striking in the Brazilian A. 

 Regnellii as in the Mexican species. Nor is the undifl^erentiated 

 corolla-tube a strong character. It seems best therefore to treat the 

 group merely as a subgenus. 



Alomia tenuifolia (the genus Lycapsus of Philippi), a xerophytic 

 shrub confined to a small island off the coast of Chili, is still ob- 

 scure. It does not appear to be represented in the leading f^uropean 

 or North American herbaria. Bentham, judging it merely by the 

 description and crabbed little figures of Philippi, placed it in Alomia. 



