Some Observations on the Breeding System of Sida spinosa (Malvaceae)

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Sida spinosa L. is a common annual, introduced weed in eastern Kansas. During the summer of 1962 I discovered a white-flowered planti of this normally yellow-flowered species growing near the Botany Greenhouse of the University of Kansas. Since white versus yellow corolla color has been one of the key characters used to separate species within this genus, there might be some merit in formally recognizing such a white-flowered form, but this is scarcely warranted on the basis of the single individual noted. While attempting to determine the method of inheritance of this white form, I made several observations in regard to the breeding system. Flower bagging tests for self-fertility revealed that plants of this species were self-compatible. The white-flowered plant open-pollinated in a population of normal yellow-flowered individuals, produced mostly white-flowered offspring (120 white; 3 yellow). The white-petalled plants, when selfed, produced like progency through four generations. The selfed yellow-flowered offspring of the original white-flowered plant produced 194 yellowand 54 white-flowered offspring. Attempts to artificially pollinate white-flowered greenhouse plants with pollen from yellow-flowers gave white-flowered offspring but a few had yellow petals. When four such yellow-flowered plants were selfed, their progenies revealed yellowto white-flowered individuals in the ratios of 52:24, 88:31, 102:27 and 57:12, respectively. All of these were well within 95% confidence limits of an expected 3:1 phenotypic ratio required to support the hypothesis that the determination of the yellow versus white forms was probably single gene controlled with the white form representing a homozygous recessive expression. It is difficult to rule out the possible presence of apomixis in this species. However, apomixis is considered unlikely on the basis of the observed segregation of whiteand yellow-petalled forms in the progency of supposed heterozygotes, and because of a frequent variation in leaf shape within progency series, although considerable consistency seemed apparent for any one plant. Meiosis appeared quite normal in all of the dividing microsporocytes which were observed using the propiono-