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Morphology of North American Species of Polygala

1929; University of Chicago Press; Volume: 88; Issue: 2 Linguagem: Inglês

10.1086/333988

1940-1205

Theo. Holm,

Botanical Research and Applications

According to the material of North American species of Polygala here examined, it would seem that some of the subsections of Orthopolygala proposed by Chodat are too heterogeneous to be considered really natural. For instance Incarnatae, comprising types so distinct as P. incarnata, P. cruciata, P. mariana, P. sanguinea, etc., are characterized by "stylus ovario longior, filiformis," which certainly applies only to P. incarnata. Moreover, the floral structure of this species (figs. 15-18) is very distinct from that of the others. The structure of Decurrentes P. lutea: "sepala cum pedicellis concrescentia i.e. pedicelli alati" was not to be found in the material here examined. The combination of P. senega and P. polygama into one subsection seems strange, when we compare the style structure and the different habit of these species, notably the cleistogamic flowers of the latter. These four species, P. incarnata, P. lutea, P. senega, and P. polygama, are so distinct from all the others that they may be classified as monotypic subsections. With reference to P. lutea, the perennial habit by means of a persisting rosette of leaves would represent one good subsectional character; the floral structure a second, because of the development of a carpophore; and the wings, persisting for some time after the fruit has dropped, represent characters of greater importance than simply specific. The characters exhibited by the internal structure are merely specific, for instance, the centric leaf structure and the cortical parenchyma being homogeneous in some species and heterogeneous in others; as well as the occurrence of oil ducts in some species and its total absence from others. The peculiar secretions which Vesque found in the chlorenchyma of several Brazilian species may be referable to oil, which Chodat observed in the leaves of many South American species, but contained in lysigenous ducts. The crystalline appearance of the secretion found by Vesque was evidently due to the preparation of dried material. In the living plants examined the oil was perfectly normal, and sometimes quite abundant. But while Chodat never observed these oil ducts in the stem of any of the South American species, they are nevertheless well represented, and very regularly indeed by some of the North American, as here described. The occurrence of secretions in Polygala, in species of limited geographic distribution in North and South America, thus represents an analogy to Viola, of which several species peculiar to Chile and eastern North America contain secretions in the roots, stems, and leaves. Finally, with reference to epharmonic characters, according to my observations Polygala shows only a very few that may be identified as such. This is especially true of P. senega from woods and dense thickets, where the leaves show a strictly dorsiventral structure, while in the other species the stomata are distributed over both faces of the blade, whether the structure of the chlorenchyma is centric or dorsiventral. And this varied structure of the chlorenchyma accompanied by the constant distribution of the stomata is exemplified by species inhabiting more or less dry or moist sandy soil in the open, and very frequently associated with each other. While the leaves are destitute of mechanical tissue, such is present in the stems of all the species examined, but only in the form of a pericycle, and of a single stratum. The presence of oil ducts may hardly represent an epharmonic character, since it is not connected with any particular environment.