Vicarious grasses, as demonstrated by a new species of Phalaris from South America

Among the grasses, preserved at the Rijksherbarium, one of the most valuable collections is certainly that of the well-known agrostologist and collector, B. BALANSA. It contains not only the types of the grasses, described by himself, but also very beautiful material, received by him from his contemporaries. All his European and Oriental grasses, those collected by him in New Caledonia, Tonkin and Java, besides a rich material from his travels in Paraguay and Argentina, are represented in this collection together with a beautiful set of ARECHAVALETA’s grasses form Uruguay. The material is in extraordinarily good condition and was very completely collected by him. I could already describe many novelties from this collection. One of these is particularly interesting on account of questions of geographical distribution. Various botanists have called attention to the fact that there is a rather striking concurrence in the floras of Argentina and some of the southern States of North America and it was STANDLEY who pointed this out, giving a list of analogous species from both countries. It is true that in some cases grasses of the southern States of North America occur in Argentina too. I have already had the opportunity to emphasize this, but generally speaking the coincidence of grasses of both parts of the earth mentioned here, is not so very large if we study the plants more intensively. What I mean is this: in many cases and at first sight, or studying the principal features, a resemblance is very striking, especially also as to the habit and the more prominent characters. But on comparing such plants from North America with the corresponding plants from Argentina, it appears in most of the cases that the two species are not identical. Argentina species of the so very difficult genus of Setaria certainly closely resemble some species from Mexico or the southern Unites States, but in my opinion, they do not belong to the same species. It was especially the genus Aristida which, after an exhaustive study, gave me a better idea of these so-called ”succedaneous“ species. As, however, such Argentina species of Aristida differed in a great many minor points from the North American representatives of this group, it was impossible to consider them as really identical and I was so convinced of their specific distinction that I did not hesitate to accept them as new species. It is not difficult to find in other genera of grasses similar convergencies which, in reality, do not exist. Resemblance is only relating to the general habit and the external or easily visible characters, but a great many minor, but very constant and not less striking characters are to be found, through which we are justified to consider them as different species.