John C. Semple
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Xanthisma texanum DC. THE TEXAS SLEEPY DAISY Herbaceous annuals native to the prairies of Texas, Oklahoma and a small area of eastern New Mexico. The genus is distinguished from relatives in the Compositae: Astereae by its two kinds of achenes and a receptacle with chaffy aveolae. Xanthisma texanum was the only species in genus until recently (see Machaeranthera); it includes two subspecies (ssp. drummondii and ssp. texanum with two varieties; var. orientalis and var. texanum confined to southern Texas). The plants are usually less than 0.5 m tall but a "giant" plant was found in 1972.
The species has been offered in the past in seed catalogues and collections of escaped cultivated plants have been made from areas greatly out of the range of distribution (e.g., northern California and North Africa). The species is notable for its accessory B chromosome first discovered and investigated by Witkus and co-workers in the 1950's and 1960's. More recent studies done by JCS are listed below.
Plants usually have 4 pairs of chromosomes (2n=8) but some have 1 to several extra chromosomes whose inheritance, morphology, meiotic behaviour and distribution in wild populations at the regional and local level were investigated in a series of studies conducted over 20 years by JCS.
Publications by J.C. Semple on Xanthisma SEMPLE, J.C. 1972. The behavior of B-chromosomes in Xanthisma texanum DC.: a non-random phenomenon. Science 175: 666. SEMPLE, J.C. 1972. The cytology, flavonoid chemistry and systematics of the Texas Sleepy Daisy Xanthisma texanum DC. (Asteraceae). Ph.D. Doctoral Dissertation, Washington University - St. Louis. SEMPLE, J.C. 1972. The behaviour of B-chromosomes in Xanthisma texanum DC.: a non-random phenomenon. Science 175: 666.SEMPLE, J.C. 1973. Chiasma formation in the sub-metacentric B-chromosome of Xanthisma texanum DC. Canad. J. Genet. Cytol. 15: 871-873. SEMPLE, J.C. 1974a. The phytogeography and systematics of Xanthisma texanum
DC. (Asteraceae): proper usage of infraspecific categories. Rhodora 76: 1-19. Last update 24 April 2009 by J.C. Semple
© 2009, J.C. Semple |
A fourteen year long study of variation in the frequency of plants with and
without B chromosomes was conducted in southwestern Oklahoma in and around Quartz Mt.
State Park. More than a thousand individuals were sampled. The conclusion of
all the research was that these extra chromosomes were "endo-parasitic"
containing genes for their own propagation but otherwise being of little or no value to
the the "host" plant. The B chromosomes may be the remnants of the
ancestral fifth pair of chromosomes.