Cyperaceæ. Of twelve species of this family existing in the herbarium, six are referrible to Cyperus, three to Fimbristylis, and three to Scirpus. Among these there is no remarkable, nor, I believe, any undescribed species. Of C. Papyrus, which, according to Captain Clapperton, grows in the Shary, there is no specimen in the collection.
Gramineæ. Of this extensive family, with which Dr. Oudney was more conversant than with any other, and to which, therefore, during the expedition, he probably paid greater attention, the herbarium contains forty-five species: and in dividing the order into two great tribes, as I have formerly proposed[121], thirty of these species belong to Poaceæ, and fifteen to Paniceæ. This relative proportion of these two tribes is considerably different from what might have been expected, in the climates in which the collection was formed: it seems, however, to be connected with the nature of the surface, for in the Great Desert the reduction of Paniceæ is still more remarkable; this tribe being to Poaceæ, in that region, in the proportion of only five to eighteen.
Dr. Oudney remarks with respect to the grasses of the desert, that he observed no species with creeping roots; for a species of Arundo related to Phragmites, which he notices as the only exception, is not properly a desert plant.
Among the very few Gramineæ deserving particular notice, the first is Avena Forskalii of Vahl. The specimens in the herbarium which were collected in the desert of Tintuma in some respects differ from all the others that I have seen of this variable species. In the Banksian herbarium there is an authentic specimen from Forskal; I have received from M. Delile specimens both of his A. Forskalii and arundinacea, described and figured in his Flore d’Egypte; and am also in possession of others in somewhat different states, collected in Egypt by M. Nectoux and Dr. Sieber. From a comparison of all these specimens, I am led to believe, that A. Forskalii and arundinacea are not specifically distinct; and it is at least evident, that arundinacea more nearly approaches to the plant of Forskal than that to which M. Delile has applied the name Forskalii.
This grass, which does not belong to Avena, is referrible to Danthonia, from the structure of the outer valve of its perianthium. But Danthonia requires subdivision into several sections, of which, perhaps, our plant may be considered as forming one.
The character of the section established on Danthonia Forskalii would chiefly consist in the very remarkable obliquity of the joints of the locusta, which is, indeed, so great, that after their separation each flower seems to have at the base an almost vertically descendent spur; and as the inferior extremity of the upper joint is produced beyond the lower, a short calcar actually exists before separation, and this calcar is equally manifest in the terminal rudiment of the locusta. The present, therefore, is a case of more remarkably oblique articulation in grasses than even that existing in Holcus acicularis (Andropogon acicularis, Retz) which led to the formation of Centrophorum; a genus still admitted by Professor Sprengel[122], and respecting the structure of which a very singular explanation has been lately offered by M. Raspail[123]. In one respect, the two cases differ. In Danthonia (Centropodia) Forskalii, the articulations being in the axis of the locusta or spicula, each flower appears to have this spur-like process; while in Holcus (Rhaphis) acicularis, the joint being in the peduncle or branch of the racemus, the spur is common to three locustæ.
Dr. Fischer, in whose herbarium the specimen was observed which led to the formation of Centrophorum, will probably recollect the communication made to him on the subject of that plant, of which Dr. Trinius himself has since corrected the characters. He retains it, however, as a distinct genus, for which he has adopted the name Rhaphis, given to it by Loureiro, by whom it was originally proposed, on other, but not more satisfactory grounds.
Triraphis Pumilio is the second plant of this family to be noticed. It is undescribed, and belongs to a genus of which the only two published species were found in the intratropical part of New Holland[124]. In several points of structure the African plant is very different from T. pungens, the first of these species; in some respects it approaches to mollis, the second species, especially in the inequality of its setæ or aristæ, but it differs from both in habit, and in having only one perfect flower in each locusta[125].
Of Pennisetum dichotomum, (Delile, Flore d’Egypte, p. 15, tab. 8, f. 1.), which, in several different states, is in the collection, it is remarked by Dr. Oudney, that “it is a great annoyance to man and beast, from the prickly calyx (involucrum);” and by Major Denham, that from Aghedem to Woodie “it covered the surface of the country, and annoyed the travellers to misery;” he observes, also, that the seed is called Kasheia, and is eaten.
Panicum turgidum, (Forsk. Arab. p. 18; Delile, Flore d’Egypte, p. 19, tab. 19, f. 2.), is also one of the most common grasses from Tripoli to Bornou.