Onagraceae Research Articles

A PROPOSED PHYLOGENY OF THE ONAGRACEAE BASED PRIMARILY ON NUMBER OF CHROMOSOMES

The family Onagraceae is such a homogenous one that the interrelationships of the constituent genera should not be difficult to determine. Moreover, as is well known, changes in number of chromosomes play an unusually conspicuous r61le in experimental phylogenetic studies in this family. There is no basic number of chromosomes common to all genera in the family, which indicates that the family probably originated from parents of dissimilar chromosomal constitution.' Postulating a ancestry renders it possible to consider at least five distinct sets of haploid chromosome numbers upon which to base a phylogenetic scheme. If the structure were based upon a single ancestor whose parents each had essentially the identical chromosomal complements, only one haploid set is available; in other words, the possible mechanical combinations are strictly limited and hardly any flexibility is possible unless polyploidy of some form intervenes, or it is assumed that the ancestor showed marked variations in the number of chromosomes.2 If we visualize one parent as an aquatic form possessing four haploid chromosomes, and the other as a probably terrestrial form with seven haploid elements, the cross between the two would therefore possess eleven haploid chromosomes. We may call the first parent A, the second B, and the hybrid C. We may assume that A and B are self-fertile and that C is capable of being back-crossed to either parent. Therefore, A + C = 15, and B + C = 18n chromosomes. All numbers so far found for any onagrad, with a few improbable exceptions,3 can be fitted nicely into this scheme. Before proceeding further, it will be necessary to mention that the chromosomal complement of any species in the following genera has not yet been ascertained: Hauya, Gayophytum, Meriolix, Diplandra, Riesenbachia, Semeiandra, Ludwigia, Heterogaura, Gongylocarpus, Burragea. Some of these have been fitted into the scheme on the basis of vegetative and morphological resemblances. Jussieua (Jussiaea), with 8n chromosomes, may be assumed to have arisen directly from A as a tetraploid genus. Parent A probably had many of the characters of Ludwigia, and there is a strong likelihood that Jussieua may have been derived from this genus. The back-cross of A with C would account for the parentage of Zauschneria. On the basis of its

The Hypostase

The Hypostase

Notes on the Flora of the Rosebud Indian Reservation, South Dakota

T HE Rosebud Indian reservation is situated in South Dakota, south of Big White river, and extends from about the middle south line of the state east to the Rosebud lands opened for settlement in 1904. It is bounded on the north by Big White river, on the east by Gregory county (the land opened up for settlement), on the south by Nebraska, and on the west by the Pine Ridge Indian reservation. The soil is sandy Loup Fork Tertiary, Miocene clays or Cretaceous black shales as one proceeds northeast across the reservation from its southwest corner. In the eastern part of this area and in the valley regions the Minnesota and east Nebraska flora prevails; in the medium elevated regions, that of the high plains; and on the high points and in the western part of the reservation, that of the Rocky Mountains. Many Canadian species are also met with. The country in early spring to the middle of the summer is a rose-flower region; hence the name, Rosebud. The Leguminos&e are also prominent flowers, but, though more numerous in species than the Rosacepe, are less conspicuous. In the summer the Leguminosve and the Evening Primrose family vie with each other. The predominating flowers of the fall season are those of the Compositae. The grass family is represented by numerous species, which are themselves very variable. The trees are usually low and spreading, and are usually found only along the streams. The following list of identified plants are the result of the author's observations during the spring, summer and fall of 1904. The work was carried on as time would permit, and, consequently, contains only a small part of the plants of the region. The books used in identifying the plants were Wood's Eastern Botany, Bessey's Botany for High Schools and Colleges, Gray's Lessons and Manual of Botany, and Coulter's Manual of Rocky Mountain Botany. The date in parentheses is that on which the first bloom of that respective plant appeared. Ranunculaceae: Anemone carolinana Walt. Numerous.